MDIA 308MDIA 308

Digital technologiesDigital technologies

Converting analog to digital

• ADC – analog to digital conversion

• An analog voltage is converted in binary code

• Binary = “two states”

• Expressed as “1/0” or “on/off”

• Each digit is called a bit

• Bits are combined into longer binary numbers or “bit words”

Converting analog to digital

• If a single digit were used to express the voltage values – there would be only two values

• By creating clusters of binary digits in longer strings, many values may be represented

• Two digits could describe four values:

00 – 11 – 10 – 01

Converting analog to digital

• The number of digits in the binary number or “bit word” is called the bit rate

• For many years the standard for consumer audio (compact disks) has been 16-bit, or binary numbers with sixteen digits

• 16-bit sampling will allow over 65,000 various combinations of digits

• 16-bit sampling produces acceptable fidelity for most puposes

Converting analog to digital

• Another variable which determines the accuracy of analog to digital conversion is the sampling rate

• Sampling rate describes how frequently the analog voltage is measured and converted into digital data

Nyquist Principle

• The Nyquist principle states that the highest frequency that can be sample is one half the sampling rate

• Thus, a sampling rate of 44,100 samples per second would accurately reproduce frequencies up to 22,050 Hz.

• Since most humans hear frequencies no higher than 20,000 Hz, 44.1 is acceptable

Sampling rate

Each red point along the timeline represents one sample

Sampling rate

A low sampling rate induces sampling error represented here as a misshapen wave form

Sampling rate

A higher sampling rate reduces sampling error represented here as a more accurate wave form

Digitization

• At best, the digital data set is an approximation of the analog voltage that was sampled

• Converting the digital data back into an analog signal will have some inherent error

Digitization

Over sampling and higher sampling rates produce more accurate wave forms

Data management

• High fidelity audio (wide frequency response and high dynamic range) requires large data sets

• HD video storage requires even larger data sets

Data management

• Down sampling or down conversion lower the sampling and bit rates to produce smaller files

• To help manage data, compression schemes remove redundancies and use “masking” of some content