17. Digital representation of sound

Question 1

What does MIDI stand for?

Answer 1

Musical Instrument Digital Interface

Question 2

What is MIDI?

Answer 2

describes a protocol, digital interface and connectors which allow a wide variety of electronic musical instruments, computers and other devices to connect and communicate with each other

Question 3

Purpose of event messages in MIDI?

Answer 3

Event messages are carried by a MIDI controller.
Event messages specify pitch and duration of notes, timbre, vibrato and volume changes and synchronises tempo between multiple devices.

Question 4

What is the purpose of MIDI?

Answer 4

Makes it possible to create music with a much smaller ensemble of musicians

Question 5

Is MIDI recording off a live source?

Answer 5

No, A set of instructions that synthesise a sound based on pre-recorded digital samples is used.

Question 6

What are the benefits of MIDI?

Answer 6

Uses less disk space, sometimes up to 1000x smaller than a standard recording at the same quality.
Music can be easily manipulated
Instructions can be passed onto different instruments and played in different ways.

Question 7

describe the digital representation of sound in terms of of sampling rate and resolution

Answer 7

sound waves are naturally in a continuous analogue form
this cannot be exactly replicated in digital form because digital is discreat
the higher the sample rate taken the closer the replication of the sound to the original analogue wave
sample resolution is the number of bits per sample
a high sampling rate is useless without a high sample resolution and vice versa

Question 8

what is sample rate measure in

Answer 8

number of samples per second (measured in Hz)

the frequency with which you record the amplitude of the sound

Question 9

when looking at sound how do you calculate file size?

Answer 9

Bit Rate * length of sound

Sample Rate * Sample Resolution * length of sound

Question 10

explain nyquist’s theorem

Answer 10

Sample Rate must be greater than twice the highest frequency component of interest in the measured signal

Question 11

compare analogue and digital, signals

Answer 11

analogue: a continuous signal which represents physical measurements
digital: discrete time signals generated by digital modulation

Question 12

compare analogue and digital, representation

Answer 12

analogue: uses a continuous range of values to represent information
digital: uses discrete or discontinuous values to represent information

Question 13

compare analogue and digital, examples of

Answer 13

analogue: human voice, mercury thermometer, tape recorder, analogue voice
digital: computers, CD’s, DVD’s, digital watch

Question 14

compare analogue and digital, data

Answer 14

in analogue technology a wave is recorded in its original form: for example a signal from a microphone can be copied onto a tape, then read, amplified and sent to a speaker to produce the sound
in digital technology, analogue waveforms are sampled at intervals, turned into a limited set of numbers and stored on a digital device

Question 15

compare analogue and digital, quantifying

Answer 15

analogue: continuously varying quantities are measured
digital: quantities are counted rather than measured

Question 16

explain the process of analogue to digital conversion

Answer 16

the ADC samples the analogue data at a given frequency, measuring the amplitude of the wave at each point and converting it into a binary value according to the resolution or audio bit depth used for each sample
to output a sound, the binary values for each sample point are translated back into analogue signals or voltage levels and sent to an amplifier connected to a speaker