8/14/2019 Music 290a HW 2

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Column A:

Analog/digital audio data structures

Digital sound on a computer is like a record of a

sound captured at many points.

Digital samples begin as continuous analogsound. This sound is made up of vibrations in theair. The process of turning analog sound into

digital is called analog-to-digitalconversion.

Digital sound is made up of discrete points.

These points depend on two things: sampling

rate and sampling width, or quantization.

The sampling rate is number of samples or points

per second in the sample.

The sampling width is how much information is

stored about each discrete point in the sample.

Digital sound is used in four different forms:

Complete Sample. A sample where all the

information about a sample is recorded and

played back digitally.

Single-tone Sample. A digitized sample thatcontains all the envelope and harmonic spectrum

information to produce a single tone of an

instrument realistically.

Single-cycle Waveform. A series of numbers

which represent only a single waveform. This is

played back repeatedly to produce one sound.

Wave Shaping. This structure utilizes filters and

algorithms to change a single waveform.

Column B:

MIDI protocol and its components

MIDI files are like sheet music for the computer,

instructing a playback device to play.

MIDI data isperformance data, which representthe way an MIDI instrument or player would

playback the piece. MIDI can be recorded by

playing a MIDI instrument, such as a MIDI

keyboard. A computer would then record

information about what is played.

MIDI is a computer language which contains

commands and data known as MIDI messages.

The MIDI protocol allows for 16 differentchannels for messages to be sent to.

Channel Messages are sent on specific MIDI

channels. There are two types, Voice and Mode.

Voice Messages contain data about what notes to

play (called voices), what the velocity of the

notes are, and any expressing properties of thenotes.

The notes range from 0 to 127. The velocity

information ranges from 0 to 127, with 1 being

very quiet and 127 being very loud.

Mode messages contain information about what

channels a MIDI device receives, and how many

voices it transmits.

General MIDI format lays down standards for all

MIDI files and MIDI devices.

General MIDI specifies common numbers for

musical instruments, timbres and percussion

sounds.

General MIDI also ensures every instrument has

16 channels and can play 16 instrument timbres

at the same time. Also, every instrument must be

able to play 24 notes simultaneously.