AN ANALYSIS OF THE

ADVANTAGES, DISADVANTAGES, AND STANDARDIZATION

OF

DIGITAL AUDIO

for

Professor Eugene O. Young

Technical writing Instructor

Texas A&M University

College Station, Texas

by

Paul Robert Teich

Student

Computing Science

April 26, 1982

i

LETTER OF TRANSMITTAL

406 C Manuel Dr.

College Station, Texas 77840

April 26, 1982

Dr. Eugene O. Young

217-D Academic and Agency Building

Texas A&M University

College Station, Texas 77843

Dear Dr. Young:

I have completed the major report for English 301 and am submitting it for

grading. The title of my report is: “An Analysis of the Advantages,

Disadvantages, and Standardization of Digital Audio.” I am a computing science

major, and my hobby is high fidelity sound reproduction. The research I did for

this paper laid the groundwork for my research project this summer, which will be

on replicating human speech inflections and accent with a digital speech

synthesizer.

The field of digital audio is very young, even when compared with the age

of digital computer technology. I believe, though, that in the next decade,

digital audio will take over a major portion of the consumer audio market. This

report is written to audiophiles who have heard about digital audio products, but

have had no exposure to literature on them. There are no books devoted to digital

audio and most articles are very technical, requiring quite a bit of knowledge

about digital computers. To get a fairly extensive knowledge of digital audio

requires days of looking for sources and reading. Some of the information was not

directly available at all, but was the result of written inquiries to various

manufacturers. I have not yet found a more comprehensive report on digital audio

than mine.

Thank you for your advice on using note cards and on revision. This is the

largest paper I have ever completed, and I am going to include it, along with my

summer research on my resume. If you have any questions about my report, please

call me at 693-5560.

Sincerely,

Paul R. Teich

ii

Table of Contents

LETTER OF TRANSMITTAL ...................................................... i

LIST OF ILLUSTRATIONS ..................................................... iv

LIST OF TABLES ............................................................ iv

ABSTRACT .................................................................. v

INTRODUCTION............................................................... 1

THE DIGITAL AUDIO PROCESS .................................................. 2

Digital Audio Recording .................................................. 2

Filtering of analog input signal ....................................... 2

Analog-to-digital conversion of signal ................................. 3

Digital Audio Playback ................................................... 6

Pickup of digital information from storage media........................ 6

Digital-to-analog conversion of binary code ............................ 6

Filtering of output signal ............................................. 7

Summary .................................................................. 7

DISADVANTAGES OF THE DIGITAL AUDIO PROCESS ................................. 7

Aliasing Distortion ...................................................... 8

Quantization Noise ...................................................... 10

ADVANTAGES OF THE DIGITAL AUDIO PROCESS ................................... 13

Specifications .......................................................... 13

Frequency response .................................................... 13

Channel separation .................................................... 13

Total harmonic distortion ............................................. 14

Wow and flutter ....................................................... 14

Signal-to-noise ratio ................................................. 14

Dynamic range ......................................................... 14

Error Detection ......................................................... 16

Parity ................................................................ 16

Cyclic redundancy check code (CREE) ................................... 17

Error Concealment ....................................................... 17

Error Correction ........................................................ 18

Other Advantages ........................................................ 20

iii

PROBLEMS WITH STANDARDIZING THE CONSUMER DIGITAL AUDIO FIELD .............. 21

Recording Formats ....................................................... 21

Sampling rate ......................................................... 22

Quantizing bits ....................................................... 24

Non-audio information ................................................. 26

Total format .......................................................... 28

Storage/Playback Systems ................................................ 28

Tape .................................................................. 29

Disc .................................................................. 29

SELECTED DIGITAL AUDIO SYSTEMS ............................................ 32

Technics by Matsushita .................................................. 32

JVC ..................................................................... 33

Sony .................................................................... 34

PCM-F1 ................................................................ 34

DAD-1X ................................................................ 34

FUTURE OF DIGITAL AUDIO ................................................... 35

Digital Audio Discs ..................................................... 35

Advantages ............................................................ 35

Disadvantages ......................................................... 37

Support ............................................................... 37

Digital Audio Today ..................................................... 38

CONCLUSION................................................................ 39

APPENDIX ................................................................. 41

GLOSSARY OF TERMINOLOGY ................................................. 41

BIBLIOGRAPHY ............................................................ 43

iv

LIST OF ILLUSTRATIONS

Figure 1 Typical analog music input ........................................ 3

Figure 2 Music signal being sampled ........................................ 4

Figure 3 Square waveform of sampled voltage levels ......................... 5

Figure 4 Aliasing Distortion ............................................... 8

Figure 5 High Frequency Sampling ........................................... 9

Figure 6 Dynamic range of magnetic recording tape ......................... 15

Figure 7 Sony Crossword code error correction method ...................... 19

Figure 8 Interfacing between 16-bit and 14-bit machines ................... 25

Figure 9 The 3M format .................................................... 28

Figure 10 Laser scanning .................................................. 31

Figure 11 Block diagram of a digital tape machine ......................... 36

LIST OF TABLES

Table 1 A Sampling of the Current Digital Audio Market .................. 11

Table 2 Groups of Manufacturers with Compatible Formats ................. 21

Table 3 Preferred Sampling Rates ....................................... 23

Table 4 Number of Quantizing Bits Used in Existing and Proposed Systems . 26

Table 5 Error Correction Methods ....................................... 27

Table 6 Storage/Playback Systems: Comparison of Characteristics ......... 32

v

ABSTRACT

This report presents the audiophile with a comprehensive view of the

digital audio field, from a description of how digital audio works to current

controversies in the field. The process of digital audio is described at a level

that requires no prior understanding of digital computers. The advantages and

disadvantages of the process are discussed, along with possible solutions and

alternatives. The problem of standardization within the digital audio field is

examined, and possible solutions are suggested. Finally, the future of digital

audio and its possible repercussions in the audio field are presented.

1

INTRODUCTION

The “Computer Revolution,” started in the mid-1960s, has been gradually

edging into the audio field for years. It started with digital FM tuning

circuits and electronically controlled turntable motors, which used quartz phase-

locked loop (PLL) circuits. In the last three or four years, microprocessor

control has been an integral part of tape decks, pre-amplifiers, and such; and it

recently has been added to equalizers and remote control devices. However, the

nature of recorded sound had not changed. Microprocessors could help get the best

possible analog recordings, but could not improve on the actual method of

recording.

Analog recording, since its invention by Thomas Edison, translates music to

an electronic equivalent. The amplitude of a voltage or current is made

proportional to the loudness of the music, and the frequency matches that of the

music on a one-to-one ratio (4:225). Digital recording takes an analog music

signal and converts it into a computer readable code. The advantage of the

digital process is that the music can be measured for computer coding with much

greater precision than the magnetic field strength of a tape can be measured

(1:132). This means that the computer code can be recorded on tape or disk; and,

when it is played back, the music is not dependent on the physical

characteristics of the tape for its reproduction.

This report will present a detailed description of the digital audio

process, as well as its advantages and disadvantages. The problem of

standardization in the field of consumer digital audio equipment will be

discussed, and some sample systems will be examined. This report assumes that

the reader is well acquainted with most aspects of high fidelity sound systems,

including specifications, measurements and technical terminology. Some working

definitions will be included in the Appendix at the end of the report.

2

Most of the Sources for this paper are from the Journal of the Audio

Engineering Society and Stereo Review Magazine, due to the fact that digital

audio is a very young field with no books published as yet. The rest of the

references are from other trade journals, informational brochures, and a passing

reference to digital audio as a future development in a recent book. Few sources

are over five pages long.

THE DIGITAL AUDIO PROCESS

Digital audio can be divided into two separate processes: digital recording

and playback. The process of digital recording consists of: (1) Filtering of the

analog input signal, (2) analog-to-digital conversion of the signal, and (3)

transfer of the digital information to the recording media. The steps involved

in digital playback are: (1) Pickup of the digital information from the recording

media, (2) digital-to-analog conversion of the binary code, and (3) filtering of

the output signal.

Digital Audio Recording

Filtering of analog input signal. First, an analog input signal, usually

from a pre-amplifier (8:560), is routed through a very sharp-cutoff, high-

frequency-cut filter. This filter, called an anti-aliasing filter, removes all

frequencies above the highest frequency to be reproduced (20:64) (see Figure 1).

In most systems, this frequency is 20 kHz.

3

Figure 1 (a) Typical analog music input from a pre-amplifier, containing very

high frequency noise (20:63).

(b) Music signal after anti-alias filtering (20:64).

Analog-to-digital conversion of signal. The voltage of the filtered analog

signal is next measured at very small, constant intervals of time. The frequency

of this sampling is determined from a mathematical model, which states that the

signal must be sampled at least at twice the highest frequency to be reproduced.

Common sampling rates are between 44 kHz and 5l kHz (23:17). To measure the

voltage of the signal at each time interval, a "sample-and-hold” circuit is used.

This circuit samples the voltage of the signal at the beginning of a time

interval, and then holds its own voltage equal to the sampled value for the

4

duration of the interval (see Figure 2). It repeats this process for each

interval to be measured (20:64).

Figure 2 Music signal being sampled (20:64).

The output of the sample-and-hold circuit is a series of voltage levels in

the form of a square wave (see Figure 3a). The voltage levels are now

individually compared to a set of reference voltage levels and they are then

translated, using an analog-to-digital (A/D) converter, to binary numbers

(34:65). Binary is a number system that uses combinations of ones and zeroes,

called "bits,” to represent numbers. The output of the converter is a string of

bits, called “binary code”, which is an accurate representation of the sample-

and-hold circuit output (see Figure 3c). The process of changing the samples

from analog to binary form is known as "quantization" (2324).

5

Figure 3 (a) Square waveform of sampled voltage levels (20:64).

(b) Waveform after being rounded off to the reference levels (20:65).

(c) Binary code generated by analog-to-digital converter.

The last step in the analog-to-digital conversion sequence is the encoding

of the binary code. This procedure inserts timing and error correction

information, in binary form, into the code. It also can merge two separate

channels for stereo. The output of the encoding step is all of the digital

information necessary for the reconstruction of the analog input signal (1:132).

The final process is the actual recording of the digital information onto

tape. This is done by translating the bits of the binary code into

6

electromagnetic pulses, which are recorded on tape in the same way an analog

signal would be recorded. The tape may now be copied, transferred onto master

audio discs, or transferred to other storage media.

Digital Audio Playback

Pickup of digital information from storage media. First, the digital

information is translated from storage media back into the string of digital

information needed to reconstruct the original analog signal (20:65).

Digital-to-analog conversion of binary code. The first process that the

digital information encounters is the removal of the timing and error correction

information. The error correction information is used to restore the parts of

the binary code that were not picked up properly, due to flaws in the storage

media or pickup mechanism. The timing information is used to control how fast

the digital information is being picked up from the storage media. As the error

correcting is finished, the binary code is put into a waiting area, called a

buffer, for temporary storage. The amount of material the buffer can hold is

limited, however, so the timing information is used to control the pickup

mechanism. For example, if digital information is being picked up and filling

the buffer too fast or too slowly, the timing information corrects the speed

deviation (20:65).

As the binary code is put into the back of the buffer, the codes for the

individual voltage levels are taken from the front. Then, they are removed at a

rate equal to the original sampling frequency which is used in the recording

process. As they are removed, they are translated, using a digital-to-analog

(D/A) converter, back into their corresponding voltage levels. The output of the

digital-to-analog conversion is a series of voltages in the form of a square

waveform. This replicates the output of the sample-and-hold circuit, with the

7

small differences due to the rounding off process during quantization of the

original waveform (20:65).

Filtering of output signal. The final stage of this process is the

changing of the square waveform into a constantly varying analog signal. This is

accomplished by an "output-smoothing" filter, which, as the anti-aliasing filter

did, removes all frequencies above the highest frequency to be reproduced. The

effect is the smoothing of the square waveform into an almost exact replica of

the input to the digital audio recording process (20:65).

Summary

A music signal to be recorded first encounters the anti-aliasing filter.

Next, the signal is sampled, and the samples are rounded off. Then, the samples

are quantized, encoded and, finally, transferred to the recording media. To

restore the music to analog form, the digital information is picked up from the

recording. It is then decoded and sent to the digital-to-analog converter. The

signal from the D/A converter is sent through an output-smoothing filter, which

results in a replica of the original music signal.

DISADVANTAGES OF THE DIGITAL AUDIO PROCESS

There are three disadvantages associated with the process of digital audio.

Aliasing distortion and quantizing noise are the two main problems. Both result

in distortion in a digital audio system, and neither of these forms of distortion

are found in analog systems. While aliasing distortion is a correctable problem,

quantizing noise is rooted in the theoretical capabilities of digital audio

(20:65-6). The third disadvantage is the cost of a digital audio system. This is

a temporary condition, however, as technological advances are already lowering

the cost of digital audio equipment (14:57).

8

Aliasing Distortion

As described earlier, there is a mathematical relationship which states

that the sampling frequency of the music must be at least twice the highest

frequency to be sampled (see Figure 4a). This assures that both the positive and

the negative halves of even the highest frequency are sampled (see Figure 4b)

(16:57).

Figure 4 (a) Comparison of properly filtered system with improperly filtered

system (3:511).

(b) 20 kHz since wave (solid line) being sampled (dotted line) at 44

kHz (16:59).

9

If a frequency above half the sampling rate is sampled, it results in an

incorrect voltage for that sample. During playback, the incorrect voltage will

show up as a lower frequency distortion (see Figure 5). This distortion is

called "aliasing" distortion, because the low frequency signal generated is a

false representation, or "alias,” of the high frequency input (20:64). Aliasing

distortion products are not harmonically related to the music, and so they are

very noticeable (3:510). The effects of aliasing distortion also include the

downgrading of the signal-to-noise ratio of the recording (23:5).

Figure 5 (a) High frequency is sampled at low point.

(b) High frequency is sampled at high point.

(c) Filtered curve is sampled.

To minimize aliasing distortion, the sampling rate must be at least twice

the highest frequency sought. Equally as important is the filtering of the input

to remove any unsought higher frequencies. This is the purpose of the anti-

aliasing filter used in the digital recording process.

10

Quantization Noise

During the quantizing step of digital recording, the sampled voltage levels

are rounded off to the nearest reference level. The reference levels are a part

of the analog-to-digital converter, and are used in the same way that the

markings on a ruler are used to approximate a value that could have very many

decimal places (3 inches compared to 3.002 inches) (20:65). "There is always a

slight error between the original signal level and the quantized value.” (23:5).

These errors are heard as noise, and are called “quantizing noise.”

To minimize quantizing noise, more closely spaced reference levels must be

used. However, this introduces two other problems. First, the finer the spacing

between reference levels, the larger the binary number needed to represent the

levels; therefore, more space is used to record the number. The more space each

number takes up, the less music fits onto a tape or disc. The second problem is

that, as the spacing gets closer, it becomes harder for the analog-to-digital

converter to tell the difference between adjacent levels (20:65). This problem

is rooted in the present limits of integrated electronic circuitry technology.

To combat these problems, it is necessary to compromise accuracy for space and

electronic considerations. How much compromise depends on the whims of the

digital audio system designers. However, when better analog-to-digital

converters and faster, cheaper, computer memory become available, there will be

no need for a tradeoff.

There are two very audible subdivisions of quantizing noise. The first is

called “granulation noise.” As the signal gets weaker (near the bottom of the

system's dynamic range), the rounding off process alters a larger percent of the

input signal. This can add a harsh, gritty distortion to the music signal. "The

subjective effect of this noise is much more unpleasant than ordinary tape hiss.”

11

To correct granulation noise, many digital recorders add a low level hiss to the

music. This changes the granulation noise to a more benign form of hiss (16:58).

The other problem is that when a signal is recorded that is larger than the

highest reference level, it is rounded to the highest reference level. The

analog recording equivalent of this is clipping, but the effect is much more

noticeable in digital audio. The solution to digital clipping is, while

recording the music, to set the recording level a few decibels lower, although

this also decreases the dynamic range of the recording (16:58).

Cost

From the viewpoint of the audio consumer, the most serious disadvantage of

digital audio is the cost. Digital system components are very expensive, though,

as pointed out in The Complete Guide to Stereo Equipment, some digital components

are “less expensive than some of the esoteric models some folks favor” (4:184).

Table l gives a random sampling of the current digital audio market.

Table 1 (30, 33, 43) A Sampling of the Current Digital Audio Market

Model

Type

Cost

Sony PCM-F1 Portable VCR audio adaptor $2,500

Hitachi PCMV100 Audio/video recorder $1,900

Sanyo VCR audio adaptor $2,900

Sharp VCR audio adaptor $2,950

Technics SVP100 Audio recorder $3,000

Sony PCM10 VCR audio adaptor $3,500

Toshiba VCR audio adaptor $3,750

JVC

VCR audio adaptor $7,500

12

There are several reasons why digital audio reproduction is so expensive,

all are by-products of digital computer technology. First, though not an

equipment cost, is the price of video cassette recorder (VCR) tape. VCR tape is

needed, because the frequency of the electronic pulse representing the binary

code is typically measured in megahertz (MHz). In the case of the Sony PCM-10,

the sampling frequency (44.056 kHz) is multiplied by 14 bits per sample and by

two channels (for stereo reproduction) to obtain 1.234 MHz with error correction

and synchronization, the resulting frequency may be as high as 2.643 MHz.

Standard audio cassette tapes cannot record such high frequencies, which is why

VCR tape is used (23:l0). Even when ordered from a warehouse supplier, VCR tape

prices range from $12.00 to above $17.00 per tape (12:2).

The reasons why digital audio equipment, itself, is so expensive deal with

current computer and integrated circuitry technology. To reduce distortion

caused by the elements in this circuitry (as happens in all audio systems), high-

speed, high-precision circuit elements are needed (23:5). In digital audio

systems, the sample-and-hold, analog-to-digital, synchronizing, and error

correction circuitry are all implemented using integrated circuitry (see

Appendix).

Integrated circuits of the complexity needed for audio applications are

very expensive to produce. Only the larger audio electronics corporations, such

as Sony, have the resources needed to design and produce their own integrated

circuitry (14:57). Other electronics companies, outside of the audio field, have

produced chips to sell to audio manufacturers. An example of an integrated

circuit produced for audio applications is the Burr-Brown Corporation's PCM75

analog-to-digital converter. There are several models, ranging from $198 to $249,

depending on the speed and distortion of each model (19:1).

13

ADVANTAGES OF THE DIGITAL AUDIO PROCESS

There are many more advantages to the digital audio process than

disadvantages. The specifications of a digital system's ability to reproduce

sound are much better than analog system specifications. Digital systems make

use of signal error detection, concealment and correction, while analog systems

do not. In addition, copying digital recordings does not degrade the sound.

There is no print-through on digital tapes; and on audio discs (analogous to

records), any wear that may occur will not affect the music.

Specifications

The specifications used to describe how well a digital audio system

reproduces music are the same as used in analog audio. The major categories are:

(1) frequency response, (2) channel separation, (3) total harmonic distortion,

(4) wow and flutter, (5) signal-to-noise ratio, and (6) dynamic range.

Frequency response. The frequency response of digital systems is limited

only in the high-frequency response. This is because of the anti-aliasing filter.

However, if the proper filter and sampling rate are used, the high-frequency

response can be extended beyond the range of human hearing. The frequency

response of a digital recording is also exceptionally flat, displaying none of

the dips, peaks and roll offs associated with analog readings. It is not

uncommon for digital recordings to display a frequency response of 0 - 20 kHz ± 1

dB (17:623).

Channel separation. When recording music digitally, the two (stereo)

channels are sampled separately. After they are converted to binary, they are

merged, giving two values (for left and right channels) for each time interval,

and then are encoded. Upon playback, the binary code is decoded, and the two

14

channels are separated and sent to separate buffers (10:65). This process

insures that the two channels do not intermix, and it gives digital audio a

channel separation specification equal to its dynamic range. For most digital

audio systems, this is equal to or greater than 90 dB (17:623). Crosstalk is

also eliminated.

Total harmonic distortion. In a digital system, harmonic distortions are

produced "only by the electronic circuits for coding and decoding” (28:520).

Given the state of modern digital technology, in most digital systems, the total

harmonic distortion can be kept equal to or below 0.05% (17:623).

Wow and flutter. During the digital-to-analog translation of digital

playback, the individual voltage levels are released from the buffer at

essentially unvarying time intervals. A crystal oscillator timing mechanism,

similar to those used in electronic watches and phase-locked turntables,

implements this (8:66). Wow and flutter is virtually eliminated from digital

systems by this process. If it does occur in greater than “unmeasurably small”

quantities, something is drastically wrong (20:65).

Signal-to-noise ratio. The signal-to-noise ratio (S/N ratio) of a system is

basically attributable to the mechanical limitations of the recording media. The

noise level in a digital recording, likened to tape hiss and surface noise in

analog recordings, is at much lower level and consists mainly of granulation

noise. There are no mechanical sources of noise in a digital system; so, for a

typical digital system, the S/N ratio should be equal to or greater than 90 dB

(again, approximating the value of the dynamic range).

Dynamic range. The most noticeable difference in the sound quality of

digital systems is in the dynamic range captured by digital recordings. In

analog recordings, very soft sounds are often buried below the noise level of the

storage media (tape hiss or record surface noise), while very loud sounds cannot

15

be recorded faithfully. Loud sounds may saturate the tape or cause the wiggles

in record grooves to overrun adjacent grooves (10:63). As a result, music to be

stored on records or tape must be "compressed”. Compression makes soft sounds

louder, and loud sounds softer. While this enables the entire musical selection

to fit onto the tape or record, "It detracts from the lifelike quality of musical

reproduction during playback” (4:225). The music on records and tapes usually

has a dynamic range of under 65 dB, compared to orchestra music, which has a

dynamic range of 85 to 95 dB (10:63) (see Figure 6).

Figure 6 Dynamic range of magnetic recording tape is approximately 60 dB, while

orchestra music has a range of 85 to 95 dB (10:63).

Because the electromagnetic pulses representing the binary code on the

magnetic tape (or the dots on the audio discs) are just a representation of the

sound, the level that they are recorded at is not important. On tape, a level

well above the residual tape hiss and well below the saturation level can be

chosen. The level of the pulses remains constant and, thus, eliminates the

disadvantages of recording analog music on tape (24:10).

16

The accuracy of digital audio techniques has been summed up by E. Brad

Meyer, of Point One Audio: "Digital sound will contain none of the frequency-

response errors, distortion, noise, flutter, and so on that are inherent in even

the best analog recording and reproducing systems" (16:56).

Error Detection

Even in the best digital systems, there will be mechanical causes for

dropouts or errors in reading the recorded music during playback (2315). These

situations, such as a scratch in a digital disc or a tape dropout, can be

disastrous in a digital system. With some types of encoding, a dropout causes a

burst of noise at the maximum possible output level on the machine. Clearly,

some form of error detection, common in computer software packages, is needed.

In fact, computer data error detection is entirely applicable to digital audio

(16:58). There are numerous error detection systems; however, only two shall be

mentioned here.

Parity. As stated earlier, binary code is a string of ones and zeroes

(bits). The binary code can be divided into groups of bits, which are called

"words,” of arbitrary length. Each word represents the level of one sampling of

the sound. All ones in a word then are counted. If the total is odd, a one is

inserted into the binary code immediately after the last bit in the word; if the

total is even, a zero is inserted in the same position. This last number is

called the parity bit. When the playback device reads the binary code from tape

or disc, it re-counts the ones in each word, comparing the results (odd or even)

to the parity bit shown. If these do not match, then an error has been detected.

Unfortunately, the parity procedure does not detect an even number of

errors within the same word, because such an error leaves the count equal to the

parity bit (even + even = even; odd + even = odd). This gives parity a 50%

17

chance of detecting an error. The single-parity-bit method is, at best, a

rudimentary means of error detection (2316).

Cyclic redundancy check code (CREE). CRCC is a method used by Sony

Corporation to provide error detection in their digital systems. It can use any

number of parity bits for each word. If the number of parity bits is "n”, then

the probability of an error being detected is 1 minus 2-n

. If "n" is 16 (as in

the Sony PCM-1600), the probability of error detection is 1 minus 2-16

= .999985

(99.9985%). This is an almost perfect error detection capability. (This

equation also describes one bit parity 1 minus 2-1

=1 minus .5 = .5). (23:6).

Error detection is only the first step in managing errors in digital

systems. Once an error has been detected, something must be done about it.

Error Concealment

To prevent the errors from affecting the quality of the sound, various

methods of concealing the error exist. There are three typical methods of error

concealment:

1. Muting: The word with the error is set to zero (muted) (23:7).

18

2. Previous word holding: The value of the word before the error is

substituted for the error (23:7).

3. Linear interpolation: The average of the two words immediately before

and after the error is substituted for the error. This is the most

accurate method of error concealment, but it assumes that the words on

either side of the error are not themselves erroneous (23:7).

Though error concealment is a great improvement over playing music with

errors in it, it is possible to go even further in retaining the quality of the

music.

Error Correction

“An error correction code not only detects the code errors but also

perfectly corrects them.” To do this, it is necessary to find out where and how

the errors have occurred. The code required to do this is very complex. To

explain how it works, a simplified description of Sony's Crossword Code is

examined in Figure 7 (23:7).

19

Figure 7 This is a simplified description of the Sony Crossword code error

correction method (23:7). To correct code errors, it is essential to

find out where and how they have occurred. This is done as follows:

(a) Data values are given for four samples of music.

(b) Numbers are inserted which, when added, total 20 (an arbitrarily

chosen number) both horizontally and vertically in each

row.

(c) The tape, itself, on which is recorded the original data values,

plus the additional numbers from each horizontal and vertical

column, respectively.

(d) Playback data values. (Note that10 is shown, rather than the 12

originally assigned in the first position).

(e) Both the top horizontal row and the left vertical row add up to

only 18, rather than the 20 originally specified. Therefore, l0

must be an incorrect value.

(f) The correct word is reproduced for playback.

NOTE: All words and correction codes are expressed in ordinary decimal

figures instead of binary codes to facilitate their

understanding.

20

Another Sony method, the cross-interleave rectification code (CIRC) can

fully correct code errors of up to 4000 bits (for a length of 2.5 mm on a digital

audio disc (27:66). This is remarkable, for a scratch that large on a

conventional record would not only destroy the musical passage, it would make the

record unplayable.

Other Advantages

There are several more advantages to digital audio; however, all of them

are by-products of the digital audio technology behind the specifications and

error-resolving techniques. Some of these are:

1. The elimination of print-through on the recordings. This is related to

the code being tape-recorded at any chosen level above the tape hiss

and below the saturation level of the tape (28:520).

2. The possibility of adding any number of alternate channels. Each

channel would still be totally separate from the others. This

suggests the possibility of bringing back quadrophonic sound or of

recording different instruments or vocals on different channels. A

user could turn the vocals off and sing along with no disturbance.

Similarly, a musician could blank out his particular instrument on the

recording and play along (29:512). This also raises the possibility

of recording comments, engineering notes (as to equalization,

microphone and speaker placement, etc.), and other non-music

information on a separate channel (29:512).

3. The possibility of mass producing tapes and audio discs with

definitely superior musical reproduction (as compared to records and

tapes currently on the market) (4:184) for a much lower cost than

today's recordings (16:56).

21

4. ". . . copies can be made from one digital machine to another without

the loss in quality that occurs with conventional recorders . . . an

exact duplicate of the signal that emerged from the recording console

at the original session" (16:58). This is because the binary code is

being recorded -- not the music.

PROBLEMS WITH STANDARDIZING THE CONSUMER DIGITAL AUDIO FIELD

Recording Formats

The standardization of recording formats is the most important issue

deciding the future of digital audio. Without standardization, the equipment

produced by one manufacturer will not directly be able to play the recordings

produced by another. The consumer would have to buy a format converter to do so;

and these, currently comprised mostly of integrated circuitry, would cost

hundreds of dollars. Digital audio is already a costly addition to a sound

system. Having to buy a converter for each format to be played would convince

most consumers that digital audio is not worth the cost. Table 2 shows which

manufacturers have equipment compatible with other manufacturers.

Table 2 (27) Groups of Manufacturers with Compatible Formats

1 2 3 4

U.S. Pioneer Philips Compact JVC Mitsubishi

Magnavox Built MCA Sony Compact

Philips

Sony Long Play

22

The recording format is a combination of sampling rate, quantization, and

non-audio information (error correction and synchronization). The only standards

set by industry for digital audio are from the electronics industry association

of Japan (EIAJ). The EIAJ standard STC-007, labeled "Consumer Use PCM Encoder-

Decoder”, sets three standards. First, it sets the number of bits used to

represent one sampling (the number of “quantizing bits”) to 14 bits. Second, it

sets the sampling rate to 44,056 Hz. Third, though it does not define what type

of error detection is required or what the decoding stage of the playback device

should do if it encounters an uncorrectable error, the standard requires that

some form of error correction be used (21:20). Though these are the first

industry standards in digital audio, they apply only to consumer equipment (not

professional equipment), and they have little influence over U.S. or other

overseas manufacturers. Without standardization of recording formats, it is

difficult (at best) to transfer a recording from one format to another (28:520).

Each part of the digital format will be examined here to provide the reader with

an idea of the scope of the standardization problem.

Sampling rate. The sampling rate has been the most widely differing factor

of the digital industry. Because most high-fidelity applications require at

least a frequency of 20 kHz, most of the sampling frequencies are above 40 kHz.

However, because the European Broadcast Union (EBU) and satellite communications

networks operate at 32 kHz, some manufacturers are considering this or some other

compatible frequency (17:621). Table 3 shows a list of audio industry leaders

and their preferred sampling rates.

23

Table 3 (3, 9, 17) Preferred Sampling Rates

Organization

Sample

Rate

Remarks

Ampex 50 kHz Absolute synchronization with

standard video film frame rates

Audio Engineering

Society (AES)

50.4 kHz High quality studio work

44.1 kHz Other studio applications

32 kHz Broadcasting applications

European Broadcasting

Union (EBU) 48 kHz Easy conversion to 32 kHz

SMPTE Video Study

Group 60 kHz

Integer samples of audio data for

frame

JVC 47.25 kHz Audio High Density (AHD) Systems

Sony/Philips 44.1 kHz Compact Audio Disc (CAD) Systems

Telefunken 48.0 kHz Mini Disk (MD) Systems

The hardest part of converting music from one digital format to another is

taking "x" samples per second and converting them to "y" samples per second. “If

system A and system B are to be directly interfaced digitally, they must both use

the same sampling rates" (3:509). If they don't have the same sampling rates,

then there must be some simple ratio between the two rates, so a digital rate

changer can be used. However, if there is no simple ratio between the rates,

then the recording must be converted back to analog, and then sampled at the new

rate (3:510). In addition, "if the conversion is from a high sampling frequency

to a lower one, a digital anti-aliasing filter must be used to take care of this

new, lower, sampling rate.” That is, the higher frequencies that can be recorded

with a higher sampling rate may be above the anti-aliasing filter's cutoff for

the lower sampling rate, so the filtering must be done digitally (17:620). Every

24

time a switch is made from one sampling frequency to another, it is accompanied

by a 4 to 6 dB loss in the S/N ratio (17:620).

While differences in sampling rates are having little impact on the

consumer digital recording market, they will have a profound effect on the pre-

recorded music market, creating a need for expensive translating devices (since

all of their circuitry is integrated). While the STC-007 sampling standard is

needed, it is not compatible with other rates. A sampling rate of 50 kHz would

satisfy all high fidelity needs, as well as mesh with standard video film frame

rates.

Quantizing bits. Digressing for a moment, a bit can be either a zero or a

one, as explained previously. Inside a computer, bits form numbers of base two

(binary). In the human number system of base l0 (decimal), each digit has the

possibility of being one of ten numbers (0 through 9). A decimal number of "n"

digits can represent any one of l0n numbers. (If "n" equals 3, then 1000 (103

)

can be represented by three digits -- 0 through 999). In binary, each digit has

two possibilities, so a binary number of "n" bits could represent any one of Zn

numbers. For a binary number of 14 bits, there would be 16,384 possible values;

and for 16 bits, there would be 65,536 possible values. If a group of 14 to 16

bits is taken as one sample of a music signal, called a word, then the possible

values of the binary number represented by the word could be equated to a set of

reference voltage levels. This is the analog-to-digital converter's task in a

digital recording system and is known as "linear quantization”.

The number of bits in a word determines the dynamic range of a digital

recording. The dynamic range equals roughly six times the number of bits, giving

a theoretical upper limit of about 84 dB dynamic range for 14-bit words and 96 dB

dynamic range for 16-bit words (10:64). Other kinds of quantization are

available, but none are as easy to implement. A type of quantization called

25

“floating point quantization" can be used to make words smaller, but it decreases

a system's S/N ratio (32508). All types of quantization use binary.

To convert from a 14-bit word to a 16-bit word, two zeroes are added to the

end of the 14-bit number. They are in the least significant places, because that

is where the difference in accuracy is. To convert from 16 bits to 14, the last

two bits are ignored, because they affect the music the least (see Figure 8)

(3:509). No dynamic range is gained from converting 14 bits to 16; however, some

dynamic range is lost converting from 16 to 14 bits.

Figure 8 Interfacing between 16-bit and 14-bit machines (7:62).

Top: Missing bits seen as zeroes.

Bottom: Two extra bits ignored.

26

The STC-007 standard calls for 14 bit linear encoding to be used in all

digital audio consumer use applications (21:20). However, most of the systems on

the market now and planned for the immediate future, use the more accurate 16-bit

words. The word size recommended by Sony and Studer is 16 bits (9:624); and the

Audio Engineering Society recently recommended 20 to 24 bits (17:621), although

the technology available for 20 or more bits is not currently feasible. For the

immediate future, 16 bits, with its 90 dB of dynamic range, is the best choice

and the one more companies are going to in their products (see Table 4).

Table 4 (8, 11, 17, 19, 25, 26) Number of Quantizing Bits Used in Existing

and Proposed Systems

Manufacturer Model Quantizing Bits Dynamic Range

*Technics SV-P100 14 84.3

*Sony PCM-F1 14/16

(switchable)

86/90

Sony DAD-1X 16 >95

Sony/Philips CAD 16 90

JVC AHD 16 90

Hitachi PCMVl00 14 85

Burr-Brown PCM75 (A/D chip) 16 90

*On the market now.

Non-audio information. The information encoded into the string of binary

code after the analog-to-digital conversion is the non-audio information. It

includes the error correction and the synchronization coder. The EIAJ STC-007

standards "provide for various levels of error correction and detection, with

27

each manufacturer able to decide and select the degree and sophistication of the

error collection used" (10:87). The standard, however, really doesn't

standardize anything; and it does not define what is to happen when an

uncorrectable error is encountered (81:20). Table 5 gives a survey of the

different error correction methods used by manufacturers in their various models.

Table 5 (23) Error Correction Methods

Manufacturer Error Correction Methods

Ampex Interleave (IL), parity word (PN), erasure

(E)

Columbia Parity (P), duplicated recording (DP)

Hitachi P, Interpolation (IP)

Matsushita P, DP

Mitsubishi Adjacent code (AC), cyclic redundancy check

code (CRCC)

Sony DP, IL, crossword code (CC), AC, modified CC,

E, P, IP

Soundstream CRCC

3M, BBC IL, CRCC, PW, E

Teac DP, IL, P

Toshiba P, previous word holding

Each manufacturer has its own synchronization, but synchronization

information, as with error correction information, is relatively easy to; remove

from the binary code and is really not a large concern in standardization. The

binary code can be run through a short computer program that strips both of these

from the words containing the audio samples.

28

Total format. The last item in format standardization is that each

manufacturer takes all of the audio and non-audio information and puts it

together in the binary code string as he sees fit. As an example, Figure 9 shows

the 3M digital format. Conversion from one format to another requires stripping

the non-audio information -- an easy job -- and then matching the number of

quantizing bits and the sampling rates.

Figure 9 The 3M format. 3M uses T6 bit linear quantizing, 50 kHz samp1ing, and

20 kHz anti-aliasing and smoother filters. Data is organized into

frames of 400 bits. There are, arranged as shown above:

16 16-bit data words (D)

8 16-bit parity words (P)

1 12-bit frame good/bad check word (CRC)

1 4-bit synchronization pulse (SYNC)

Storage/Playback Systems

In digital audio, as with analog audio, there are two general methods of

storing the music. The first is magnetic tape. As discussed earlier, the binary

bits are translated into electromagnetic pulses and recorded in the material of

the tape. The second is storing the music on a rotating disc. There are many

methods of implementing disc storage in a digital audio system, unlike analog

audio, in which records all operate on essentially the same format.

29

Tape. Standardization of digital tape recording formats is not very

important, due to the fact that tape recording systems are more commonly used for

home recording than for playing back pre-recorded material (4:226). This is

supported by the recent addition of digital tape recorders to several companies‘

lines of consumer products. (The recordings from each format are not compatible

with the other formats).

Disc. Unlike tape, a disc-- whether analog or digital -- cannot be

recorded on at home. Once a disc is mastered, nothing can be done to it to add

more music. Different disc formats mean that several discs and playback units

will not be compatible. Therefore, it is extremely important that storage and

playback equipment be standardized.

There are three classes of disc playback devices, each with its own type of

disc. They are classed as to how the information is transferred from disc. The

first type, and closest in principle of operation to the analog record uses

piezoelectric detection. The digital information is recorded on a polyvinyl

chloride (PVC) disc -- the same material used currently in analog records. The

pickup device looks like an analog cartridge. However, the stylus is blunter,

for better wear, and the cartridge contains a piezoelectric transducer instead of

a magnetic transducer. The digital information is recorded as very small ridges

in a groove, much like a conventional record. The ridges cause the stylus to

vibrate; and the piezoelectric transducer in the cartridge translates the

vibration to an electric signal, which can then be processed digitally. This

method, like in analog records, is susceptible to wear, both to the disc and to

the stylus (29:5l2).

The second class of digital playback devices uses electrostatic detection.

This type of device is a spin-off of computer data storage technology. The

digitized music is stored by inducing small amounts of static electricity into

30

the disc. The discs are made of a mixture of PVC and carbon. The carbon holds

the electrostatic charge. Two types of detection schemes are currently

implemented. In the first, the electric charges are aligned within a groove. A

blunt device rides in the groove, detecting the charges. 0f course, with the

mechanical contact, there is wear to the disc and to the stylus. In the second

type of detection, a detector rides over the surface of an ungrooved disc. The

information is still recorded in a line that spirals toward the center of the

disc but, when the disc is rotating, the detector is kept over the line by an

electromechanical tracking device. The detector never touches the surface of the

disc, so no wear is induced. More data can be stored on the second type, because

the static charges can be confined to a width smaller than any groove needed to

guide a pickup device. Computers use this method to access information from

their disc drives (29:512).

The third class of playback devices uses photoelectric detection.

Photoelectric detection essentially consists of shining the light of a small,

low-intensity laser onto the disc. The light from the laser is reflected from

pits in the disc. These reflections can be decoded into the digital information

necessary to rebuild the music. There are two methods of storing the information

on a "laser disc.” The first method, now is use for video laser disc

applications, uses small pits of varying depth etched into a PVC disc with a

high-intensity laser. The playback laser is reflected, with varying degrees of

intensity, from the pits. The digital information is decoded from the intensity

of the reflections. The second method uses a PVC disc coated with a thin layer

of metal. A high-intensity laser etches holes in the layer of metal. The holes

vary in length, not depth. When the disc is being read, a low-intensity laser

scans the disc, looking for the non-reflecting holes in it (24:12) (see Figure

10). The lengths of the non-reflecting portions can be translated directly into

31

bits. Both of the laser discs are coated in a clear plastic in order to prevent

damage to the stored information (29:512).

Figure 10 Laser scanning. The surface of the audio disc:

(a) Is scanned by a beam of laser light;

(b) Focused by a lens;

(c) And the focused beam of light

(d) Is reflected from the PVC surface and measured by sensors

(7:62).

There are no current industry standards, or even preferences, for anyone

storage/playback system. For a comparison of characteristics favored by industry

leaders, see Table 6.

32

Table 6 (5, 7, 11, 29) Storage/Playback Systems: Comparison of

Characteristics Favored by Industry Leaders

Item

AES Digital

Audio

Technical

Committee

Telefunken/

Teledec Sony/Philips JVC

Channels 2/4 4 2 4

Revolutions /

Minute (R/M) Not given 278-695

Not given in

R/M 900

Diameter 300 mm max. 135 mm 120 mm 260 mm

Playing time 80 minutes

(two sides)

120 minutes

(two sides)

60 minutes

(one side) 120 min

Type Not given Piezoelectric Photoelectric Electrostatic

SELECTED DIGITAL AUDIO SYSTEMS

The following systems represent equipment manufactured by, or to be

manufactured by, leading corporations in the digital audio field. Availability

of information was the deciding factor in choosing the systems to be reviewed.

No information is available on the organization of their digital formats.

Technics by Matsushita

The Technics SV-P100 Digital Cassette Recorder is the first piece of

digital equipment to appear on the consumer market. Introduced in early 1982, it

was the first to be reviewed by a major trade magazine (Stereo Review, March

1982). The cost of the SV-P100 is $3,000 (26:46). Craig Start, testing the

cassette deck for Stereo Review, commented, ". . . It was the cleanest sound I

have ever recorded, and I've recorded a lot. To me, that says a lot about the

SV-P100‘s capabilities” (26:46).

33

Technics records on standard video tapes, and its specifications are

(26:42):

Sample rate: 44,045 Hz

Quantization: 14 bit linear

Dynamic range: 84.3 dB

Distortion: <.01%

Wow and flutter: Unmeasurable

Signal—to-noise: >80.3 dB

Frequency response: 2 Hz — 20 kHz + 0/-2.5 dB

JVC

JVC's audio high density (AHD) digital audio disc system is not yet on the

market, but it is expected within two years. It uses a grooveless electro-

tracking capacitance pickup system (11:70). The specifications of the disc and

playback system are shown below. The JVC AHD system is unique among the

forthcoming audio disc systems in that it has the capacity to playback visual

information in the form of still pictures or slow motion. The disc can also be

played on JVC s video high density (VHD) video playback system, which is now on

the market. Some of the non-audio information will be used as a guide for a

music search capability, locating the beginning of each music track. The AHD

system provides four channels of information -- three for audio purposes, and one

for video. Two of the audio channels will be used for stereo, leaving one free

for special effects, album notes, engineering notes, or for any other as-yet-

unthought-of purposes (11:68)

JVC's ADH disc specifications are (11:70):

Disc size: 260 mm (10 inches)

Revolutions: 900 (R/M)

Playing time: 2 Hours (one per side)

Channels: 3 audio (2 stereo; 1 extra); 1 video

Quantization: 16 bit linear

Sample rate: 47.25 kHz

34

Sony

Sony Corporation, being one of the front-runners in the digital audio

"revolution" (to turn a phrase), has an entrant both in the tape recorder and the

audio disc categories. The PCM-F1 Portable Digital-Audio Adaptor was introduced

to the market in early 1982, while the Digital Audio Disc (DAD)-1X is awaiting

further standardizations in the digital audio field.

PCM-F1. The Sony PCM-F1 Portable Digital-Audio Adaptor turns any NTSC-

standard video recorder into a two channel digital audio recorder costs $1,900,

assuming it has a video recorder to plug into. If not, a video recorder will

cost $800 to $1,200 more (12:2). The PCM-F1 has a switchable quantizer for either

14 or 16 bit linear quantizing, so that the consumer can decide the accuracy he

needs, compared with how much music he wants to fit on a tape (25:13).

The Sony PCM-F1 Portable Digital-Audio Adaptor specifications are (25:13):

Quantization: 14 bit and 16 bit (both linear)

Dynamic range: 86 dB/14 bit and 90 dB/16 bit

Harmonic distortion: 0.01%/14 bit and 0.007%/16 bit

Sampling rate: 44.056 kHz

Frequency response: 10-20 kHz ± 0.5 dB

Wow and flutter: Unmeasurable

Weight: 8.75 lbs.

DAD-1X. The DAD-1X Long-Play Digital Audio Disc System uses a

photoelectric detection system on PVC discs coated with a reflective layer of

metal. The specifications for this system are as follows (8:977):

Disc size: 303 mm

Playing time: 2.5 hours (single side)

Revolutions: 450 R/M

Channels: 2

Sampling rate: 44.056 kHz

Quantization: 16 bit linear

Dynamic range: >95 dB

Harmonic distortion: 0.03%

Frequency response: 2-20 kHz ± .25 dB

Wow and flutter: Undetectable

Error detection: Cross interleave

35

Note that both of the tape decks reviewed (the only two currently on the

market for consumer use) abide by the EIAJ standards, having been manufactured in

Japan. Sony's digital disc system chose the more accurate 16-bit quantization,

being strictly a decoding system (only able to play the discs). For an

illustration of the working of digital tape decks, see Figure 11.

FUTURE OF DIGITAL AUDIO

Digital audio is still a young science. The first digital cassette

recorders have been on the market for only a few months (26:40), but their effect

has been enormous. The digital recorder is now the most accurate component of

consumer stereo systems -- so accurate that it has exposed handicaps in the

response of most amplifiers and speakers that were not previously a matter of

concern. The coming of the digital audio disc, delayed because of technological

and standardization problems, is heralded by many as the end of the analog

record. But, while the digital disc is superior to conventional records, some

argue that the manufacturers have too much money invested in the production of

the latter to make them obsolete overnight. Along with this argument, there is

the possibility that a selection of non-compatible digital disc systems might

turn the consumer away from digital audio.

Digital Audio Discs

Advantages. The digital audio disc is a vastly superior method of re-

producing sound than on conventional records. All of the shortcomings of

conventional turntables will be circumvented. There will be no inner-groove

distortion, tracking error, tone-arm resonances and record and stylus wear.

Digital discs will not suffer nearly as much as analog records from the effects

36

Figure 11 Block diagram of a digital tape machine having analog inputs and outputs (15:560).

37

of poor vinyl, bad pressings, dust or any of the other problems associated with

the manufacturing and use of the discs (16:56). The digital discs should last

indefinitely, as the only wear that they encounter is being taken out of their

cover to be put in the player. Another advantage is that digital discs may

become cheaper to produce than conventional records (4:184).

Disadvantages. When home digital disc playback systems appear on the

market, possibly in early 1983 (16:56), they will be handicapped in two areas.

One is that the record companies "have invested hundreds of millions of dollars

in conventional record-making equipment.” They will not render their equipment

obsolete without hard evidence that the digital discs will sell. Therefore, they

will not issue a large selection of the digital discs until they are sure that "a

large listening audience has the equipment to play them.” The second problem is

that "the consumer is not likely to buy a digital disc player until there is a

large selection of digital discs to play on it (4:184).” Therein lies the

possibility of a stalemate, as when quadraphonic records were introduced. The

quadraphonic records could be played on existing equipment, but few records were

marketed, so the public became disenchanted with "quad" sound (4:226). There is

little chance of this happening, however. Audio companies, such as Sony, have

spent millions of dollars on digital 14:54). The situation is more like that of

the audio manufacturers abandoning the 78 RPM record for the longer playing 45

and 33 RPM records. The better method -- in this case, the digital disc -- will

win out, but there will be a long transition period (4:184). Analog recordings

could survive up to twenty years in the presence of digital discs.

Support. At the l98l audio fair in Tokyo, about twenty companies dis-

played prototype compact digital-audio-disc (CDAD) players, although only a half-

dozen or so actually had working models (14:57). Toshiba, Denon and Yamaha have

38

adopted the joint Sony/Philips "compact disc" (CD) format (12:53), perhaps

signaling the beginning of informal standardization of the audio disc field.

Digital Audio Today

With digital recorders already on the market, audiophiles are re-examining

previously acceptable performance standards for other components in the chain of

audio reproduction. Because of digital audio‘s wide dynamic range, sharp peaks

(transients from percussion and other sources) to which analog systems cannot

react fast enough for them to record fully, can be recorded. These peaks,

requiring up to 100 times the average power of the music to reproduce, will

result in clipping by most amplifiers-and, sometimes, may even activate speaker

protection circuitry (22:63). Some of the newest amplifiers on the market can

handle these very sharp transients, but they are very expensive. However, safe

headroom is vital to digital recording. Instantaneous true peak reading meters

are necessary, therefore, on digital equipment in order to avoid amplifier

overload (2:244). But, though existing equipment may not be ready for digital

audio, Robert Berkovitz, director of research for Teledyne Acoustic Research

(manufacturers of the AR speaker series) said, "Most of the analog recordings

made during the past decade will be perfectly suited to reproduction on home

digital playback equipment (once they are converted to a digital format)"

(22.61).

Though digital accuracy is a fact, there has been concern by some hard core

audiophiles that digitally recorded music is unwholesome - that somewhere in the

process, detrimental factors creep into the music. At the 1980 Spring Audio

Engineering Society Convention in Los Angeles, Dr. John Diamond, a psychiatrist,

attempted to prove that digitally recorded music produces stress and fatigue in

listeners. Though his experiments were loosely controlled, if controlled at all,

39

they started some serious debate as to what kinds of affects digitizing adds to

the music, even if any changes imparted to the music have no audible effects on

the human ear (16:59). However, “A comparison test between all the major digital

recorders and a professional half-inch-tape, two-track analog machine running at

30 inches per second that was conducted at the Sound Emporium in Nashville last

summer confirmed that there do not seem to be any major degradations ascribable

to the digital process" (16:59).

CONCLUSION

Digital audio reproduction is the most significant development in the audio

field to occur in at least the last two decades. Toshit Doi, manager of Sony's

Digital Audio Project, says, "Before digital audio was introduced, the quality

bottleneck of the whole audio chain was in analog tape recorders and analog

records.” The weakest points are now the transducers (microphones and

loudspeakers) (22:63).

Remember, however, that “the accuracy of the digital process depends on the

sampling and quantization processes" (1:132). State-of-the-art integrated

circuitry can be improved upon, and advances in technology can make digital audio

even more accurate than it is now. If the field of digital audio is rigidly

standardized, the benefits of these technological advantages could be severely

delayed, and there would be no way to get more information out of earlier digital

recordings (16:59).

Of the possible technological advances, there is one that could make

digital tape recorders and audio discs obsolete before they have a chance to gain

a large acceptance. Static Systems Corporation, New York, has developed a system

called the Sonadisc. It is a microprocessor based audio player that uses a coin-

40

sized disc, containing magnetic bubble memory (a state-of-the-art computer memory

technology), to store music. The device has no moving parts, because all of the

music is accessed electronically from the bubble memory disc. The memory disc is

inserted into a receptacle in the player and currently stores only about a

second's worth of music (one megabit's worth). A radical advance in magnetic

bubble memory devices would definitely increase the amount of storage available

(6:6). If, and when, this happens, it will certainly be a more efficient way to

store music.

I believe that the EIAJ STC-007 standard is already obsolete. Sixteen- bit

systems, sampling at a higher rate than 41 kHz, have dramatically better

specifications. Manufacturers realize this, so when the digital audio disc

enters the market, it will not be in accordance with the EIAJ standards.

I favor using an industrial coalition -- the type Sony and Philips have

formed -- to informally standardize the field. This approach assures that

technological advances would reach the marketplace faster than under stringent

governmental industrial standards. I do believe that a standardization of

digital tape deck formats is necessary to accommodate music exchanges between

systems without the need for a converter. This will eventually happen; but, for

now, just having digital tape decks available for consumer use is a big enough

plus.

Digital audio recording and playback are the future of audio reproduction,

and the sooner they reach maturity, the sooner we can stop losing our heritage of

music to the degradations of analog storage media.

41

APPENDIX

GLOSSARY OF TERMINOLOGY

(Taken from The Complete Guide to Stereo Equipment)

Channel separation: Electrical or acoustical difference between left and right

channels in stereo.

Crosstalk: Signal leakage between two channels.

Decibel (dB): Numerical expression of acoustic or electrical ratios, such as

relative intensity of sound or relative strength of signal.

Distortion: Unwanted noise, or sounds that did not exist in studio when original

recording was made. All distortion is undesirable.

Dropout: Momentary loss of signal during tape recording or playback caused by

tape defects.

Dynamic range: Span in volume, expressed in decibels, between loudest and

softest sounds.

Filter: A circuit which attenuates signals above, below or at a particular

frequency.

Frequency: Rule of repetition, in cycles per second (cps), or musical pitch and

of electrical signals, expressed in Hertz (Hz). Low frequencies refer to

bass tones; high frequencies to treble tones.

Frequency range: Range from highest to lowest pitch sounds at usable volume

level.

Frequency response: Ability to reproduce given range of frequencies.

Harmonic distortion: Disturbs original relationship between naturally related

tones and is expressed in percentages.

Head room: Margin between maximum levels indicated on recorder's volume

indicator and actual level of severe tape overload.

Hertz: Name given to number of vibrations or cycles per second in electrical

signal of alternating current. Abbreviated Hz, with capital "H"; but when

spelled out, only lower-case letters are employed. The name derives from

Heinrich Hertz, early electrical scientist.

Integrated circuit (IC): Combination of transistors, diodes and resistors

assembled in pre-packaged circuit capable of providing high gain, low

distortion, and easily controllable performance in extremely miniaturized

form.

Kilohertz (kHz): 1,000 hertz.

42

Megahertz (MHZ): 1,000,000 hertz

Noise: Extraneous sound or signal that intrudes into original as result of

environmental noise, distortion, hum, or defective parts and tubes in

equipment.

Saturation: Condition whereby tape has reached its maximum degree of

magnetization.

Separation: Degree to which stereo signals are kept apart in passing through

reproducing systems.

Signal: Electrical replica of actual sound; in broadcasting, carrier wave

itself.

Signal-to-noise ratio: Often abbreviated “S/N ratio"; relative amount of signal

to undesired and extraneous noises in any device or its output.

Transducer: Device for changing one form of energy into another. Microphone and

phone pickup are sound-to-electrical energy transducers.

Transient: Heavy burst of music, causing the amplitude of the music signal to

increase sharply and then subside.

Wow and flutter: Fluctuations in speed of turntable or tape transport that cause

pitch distortions; wow refers to slow, repeated fluctuations; flutter to

short, rapid fluctuations.

43

BIBLIOGRAPHY

1. Bayliff, R. W. "Digital techniques and the gramophone record.” Gramophone.

vo1. 57, no. 673, June 1979, pp. 131-2, 135.

2. Burkowitz, P. K. "User‘s note on digital audio standard code and procedures,

operational requirements.” Journal of the Audio Engineering Society. Apri1

1978, PP. 242, 244, 246.

3. Busby, E. S. "Digital audio recording on videotape: Some choices." SMPTE

Journal. vol. 89, no. 7, July 1980, pp. 508-12.

4. The Complete Guide to Stereo Equipment. New York: Simon and Schuster

Publishers, 1979.

5. Digital Audio Technical Committee. “Digital audio disk standardization

Conference.” Journal of the Audio Engineering Society. July/August 1980,

pp. 525-27.

6. "Digital music at home.” Computer Music Journal. vol. 5, no. 4, 1981, p.

6.

7. Doi, T. T. “General information on a compact digital audio disk.” Journal

of the Audio Engineering Society. January/February 1981, pp. 60, 62.

8. Doi, T. T., et al. "A long play digital audio disk system.” Journal of the

Audio Engineering Society. December 1979, pp. 975-81.

9. Doi, T. T. and Roger Lagadex. “An outline of the format jointly supported by

Sony and Studer for stationary-head digital audio recording.” Journal of the

Audio Engineering Society. September 1980, p. 624.

10. Feldman, L. "Digital audio for the 1980's." Radio Electron. June 1980, pp.

63-5, 87.

11. Hidaka, T. "JVC AHD digital audio disk system." Journal of the Audio

Engineering Society. January/February 1981, pp. 68, 70.

12. Illinois Audio Catalog. Chicago, Illinois Audio, 1982.

13. “JVC digital audio products.” Computer Music Journal. vol. 5, no. 4, 1981,

pp. 89-90.

14. Klein, Larry. “Audio fair in Tokyo (Oct. ‘81).” Stereo Review. February

1982, pp. 56-60.

15. McCracken, J. A. “A high-performance digital audio recorder.” Journal of

the Audio Engineering Society. July/August 1981, p. 560.

16. Meyer, E. Brad. "Digital.” Stereo Review. Apri1 1982, pp. 56-9.

44

17. "Minutes of the meeting of the Digital Audio Technical Committee." Journal

of the Audio Engineering Society. September 1981, pp. 620-24.

18. "New audio products at Las Vegas CES.” Stereo Review. May 1982, pp. 53-6.

19. PCM75: Designed for Audio. Tucson, Burr-Brown Research Corporation, July

1981.

20. Ranada, David. “Digital audio: A primer.” Stereo Review. February 1981, pp.

63-5.

21. Ranada, David. “Good news: Digital recording standards." Stereo Review.

March 1980, p. 20.

22. Ranada, David. "Superdiscs.” Stereo Review. December 1980, pp. 61-4, 67.

23. Sony‘s Digital Audio Technology - QA. Japan, Sony Corporation, nd.

24. Sony's Digital Audio - The Next Step. Japan, Sony Corporation, May 1981.

25. “Sony‘s small, portable digital audio adaptor." Stereo Review. May 1982, p.

13.

26. Stark, Craig. "Equipment test reports: Technics SV-P100 digital cassette

recorder." Stereo Review. March 1982, pp .40, 42, 46.

27. Traiman, Steve. “Digital decade: The audio/visual future.” Stereo Review.

January 1980, pp. 69-72.

28. Weisser, A. “The digital recording of sound in broadcasting.” SMPTE

Journal. July 1980, pp. 520-4.

29. Welland, K. and H. Redlich. “The MD (Mini Disk) system: A contribution to

the digital audio disk standard.” Journal of the Audio Engineering Society.

July/August 1980, pp. 510-14.