TA212 The Technology of Music Steve Wells. Tutorial 4 TMA04 –cutoff date January 22nd Block 4 Part...

TA212The Technology of Music

Steve Wells

Tutorial 4

• TMA04– cutoff date January 22nd

• Block 4 Part 1– starts February 15th

TA212 The Technology of Music

Tutorial 4

• TMA04– cutoff date January 22nd

• Block 4 Part 1– starts February 15th


Block 4 Part 1 doesn’t start until February 15th...

but we don’t have another tutorial until April 12th... !

TMA04

• Question 1 – Basics of Instruments– vibrators, percussion, damping– calculations based on vibrating plate

• Question 2 - Clarinet– reed, transposition– frequency analysis in Audition


TMA04

• Question 3 - Brass instruments– mouthpiece, bell, mute, valve

• Question 4 - Violin– bow, bridge– calculations based on strings


Calculations in TMAs

• ALWAYS quote any formula you are using• ALWAYS define the terms in the formula


f1: fundamental frequency (Hz)

L: length of the string (m)

T: tension in the string (N)

µ: mass per unit length (kg/m)

Calculations in TMAs

• Save any rounding of results until the end• Rounding of intermediate results leads to errors• Example from TMA03


This is the rms voltage.

To get the peak to peak we need:


Block 4: Sound Processes

• Desktop Sound• Notation and Representation• Carillon to MIDI• Music Distribution• The Music Business

Desktop Sound

TA212: Block 4, Chapter 1

TA212 - Block 4 - Chapter 1 - Desktop Sound

Three Stages

• Collect the sound• Edit, Mix and Add Effects• Distribute the Result

• The three stages are sometimes marked on CDs to show whether analogue or digital technology was used at each stage:

A D D D D D

Analogue Input - Sensitivity

• Signal Amplitude• High Sensitivity

– microphones etc.• Low Sensitivity (“Line”)

– synthesisers etc.


Specifying Sensitivity (revision)


RMS amplitude is the amplitude equivalent to a non oscillating source carrying the same power.

rms amplitude

amplitudedermsamplitu 71.0

amplitude

peak to peak amplitude


Decibels (again!)

• Think of voltages and power as analogues of sound• Sound level is measured in dB - so can voltages and

power• Need to define the zero point

– 0dBu is defined as an rms voltage of 0.775 volts– 0dbV is defined as an rms voltage of 1 volt– 0dBm is defined as a power of 1 mW


Decibels – standard values

• - 20dB one tenth of the voltage/power• + 20dB ten times the voltage/power• - 6dB half the voltage/power• + 6dB twice the voltage/power

Impedance (revision)

• Equivalent of electrical resistance for an oscillating signal

• Varies with frequency– but this is usually not specified

• Impedance matching– Get it wrong and you lose power


Impedance Matching


low high

low

high

high

veryhigh

highlow

Pre-amplifier

Analogue Output - Clipping


• The clipped signal has been amplified too much and the extremes of the amplitude have been lost

• Very unpleasant sound!

TRS Connector

TA212 - Block 4 - Chapter 1 – Desktop Sound

Tip

Ring

Sleeve

Insulation to separate the connections

3.5mm TRS Connector


Speakers

Left Channel

Right Channel

Ground (0v)

3.5mm TRS Connector


Speakers Microphone

Left Channel

Right Channel

Ground (0v) Ground (0v)

Preamp Power (5v)

Signal

For high impedance microphones (such as electrets), 5 volts is supplied to the microphone to drive an in-built preamplifier


Cables

• screened leads• balanced leads signal wire

earth

earth

two signal wires twisted together


Balanced Cables


Digital Interfaces

• Standards– AES/ABU– S/PDIF– MADI

• Essentially the same!• Serial transmission

– one bit at a time• Real Time• USB and Firewire also used on desktop systems


Digital Storage

• Compact Disc (CD)• MiniDisc (MD)• Digital Versatile Disc (DVD)• Magnetic Tape• Hard Disk• Solid State memory


Digital Storage Issues

• What stage of the recording process?• Initial Recording

– high capacity required– Magnetic Tape or Hard disk

• Digital Mixing– Random Access– Hard Disk

• Delivery– CD etc.


Digital File Formats

• All have basically the same structure– based on “Interchange File Format” (IFF)

• Built from “chunks”– All chunks consist of

• identity• size• data

– The data part of a chunk can contain other chunks.


Chunk Structure

Identity

Size

Data

4 bytes

4 bytes

Size bytes


WAV File

“RIFF”

Size

4 bytes

4 bytes

Size bytesFormat Chunk

Data Chunk

“WAVE”


WAV Format Chunk

“FMT ”

Size

Sound Parameters

• Format of data

• number of tracks

• sample rate

• etc.


WAV Data Chunk

“DATA”

Size

Sound Samples

• Actual Sound Samples


Editing

• Combining many sound sources to produce a single stereo image which can be recorded to CD– adjustment of levels– mixing different takes to remove imperfections– adding effects

• Edit Lists– Non-Destructive– real time


Setting the Levels

• Normalisation– Setting the final levels based on the loudest part of the

recording– Setting the levels to -6dB means setting the loudest

part of the recording to 6dB below clipping.• Compression and Limiting

– Reduce the output level when the input level is high– Reduces the dynamic range

• Expansion and Gating– Increase the output level when the input level is low– Reduces the dynamic range

Mixing

• During recording several microphones are used to record individual performers or groups

• Mixing is the process of combining these individual recordings– Adjusting the levels of

individual tracks



Controlling the Level

• analogue signals when added can produce clipping• digital signals run out of space!

– two 16 bit samples when added will require 17 bits.• two approaches

– increase the capacity in the mixing stage– reduce the sample sizes (downsizing)

• a 1 bit reduction halves the sample value

Carillon to MIDI

TA212: Block 4, Chapter 3

TA212 - Block 4 - Chapter 3 - Carillon to MIDI

What is MIDI?

• Musical Instrument Digital Interface• a way to carry information about music from one

place to another along a wire or in a file– which note to play– when to start– which instrument to use


MIDI Connections

Synthesiser

MIDI Out

MIDI Thru

MIDI In

“local off” switch


MIDI Messages

• Instructions about what sounds to make• Status byte

– note on– note off– program change (new instrument)

• Data byte(s)– numerical information

• pitch, volume etc.


MIDI Channels

• MIDI can support 16 channels. Each can be a separate synthesised instrument

• Status bytes which refer to channels are arranged in blocks of 16

• So...– 144: “Note On” on Channel 1– 145: “Note On” on Channel 2– etc.


MIDI Example

145

60

64

129

60

64

Note On - Channel 2

Middle C (C4)

Mid range velocity (loudness)

Note Off - Channel 2

Middle C (C4)

Mid range velocity (loudness)


Running Status

• When repeating a message with the same status as the last message– just send the data– the status is implied

• Don’t need to use NOTE OFF - just use NOTE ON again with a velocity of 0

• With a lot of notes this can save a lot of status bytes.


• Without running status:– 146, 60, 64, 146, 64,64, 130, 60, 64, 130, 64, 64

• With running status:– 146, 60, 64, 64,64, 130, 60, 64, 64, 64

Running Status Example

Repeated status bytes

Repeated status bytes removed


MIDI File

• Standard MIDI File uses the Interchange File Format– like a WAV file

• Fixed size Header Chunk• One Track Chunk per MIDI Track


SMF Header Chunk

“MThd”

Size (always 6 bytes)

4 bytes

4 bytes

Format type

No. of Tracks

Time

2 bytes

2 bytes

2 bytes

0: One Track1: Many tracks

played together2: Many tracks

played in sequence

+ve: number of clock ticks per crotchet-ve: number of ticks between SMPTE Time Frames


SMF Track Chunk

“MTrk”

Size

MIDI Events

One Chunk per Track

Each MIDI Event consists of:

• Delta Time

• MIDI Message

–Status Byte

–Data Bytes


Contacting Me

• Phone

01454-850379• Email

[email protected]• Web

http://www.stevesphotosite.co.uk/ta212


Questions

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