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CMSHN1114/CMSCD1011 CMSHN1114/CMSCD1011 Introduction to Computer AudioIntroduction to Computer Audio

Lecture 9: Computer audio applications

Dr David EnglandSchool of Computing and Mathematical Sciences

http://java.cms.livjm.ac.uk/homepage/staff/cmsdengl/Teaching/cmscd1011.html

Email: d.england@livjm.ac.uk

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In this session...In this session...

• We will look at the applications of computer audio which are applicable to:– Music creation– Multimedia development– Game development– Video and audio post-production

• The techniques include:– Direct to disk recording– Notation– Algorithmic composition

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Computer audioComputer audio

• The term computer audio represents quite a broad spectrum of applications

• This is because we have both MIDI applications and digital audio applications each of which is suitable for a number of tasks

• When combined they provide a very powerful platform for audio delivery

• It is useful to consider the pros and cons of each...

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Pros and cons of digital audioPros and cons of digital audio

• Pros– If attention is paid to the Nyquist theorem, digital

sampling can accurately capture all sound characteristics

– PCM requires very little hardware processing– Digital data does not degrade when re-recorded, unlike

analogue recordings on magnetic tape• Non-destructive editing / Instantaneous copying

• Cons– Digital audio can demand huge file and memory sizes

as well as high data rates– Compression can consume more processing time– Exact digital copies of music frightens the music

industry!

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Pros and cons of MIDIPros and cons of MIDI

• Pros– MIDI data is very efficient for transmission of

musical performances, MIDI files are extremely small

– Is standard across many types of device

• Cons– MIDI only captures the performance data, not the

actual sound that is produced– The quality of the audio is determined by the

quality of the tone generator– MIDI is a serial protocol and its data rate is fixed at

31,250 bits per second– The MIDI file format cannot be used for digital audio

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A taxonomy of computer audio A taxonomy of computer audio applicationsapplications

Sequencer

Notation (DTP)

Patch editor / librarian

Algorithmic composer

Digital multitrack recorder

Digital audio editor

Musician Sound engineer / producer Multimediadeveloper

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Direct-to-disk recordingDirect-to-disk recording

• Direct-to-disk recorders aim to provide all the functionality of analogue multi-track tape recorders whilst adding all the good aspects of digital audio– Multi-track recording is the recording of more than one

track of audio at the same time

• Can apply digital effects in real-time at playback– Requires lots of processing power– Does not alter the actual digital audio on disk

• Non-destructive editing is possible with digital data– Edit Decision Lists (EDL) are used to control the

playback of the digital audio

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Edit Decision ListsEdit Decision Lists

Original recording

Segment 1 Segment 2 Segment 3

Each segment is marked (i.e. its start and end points are noted)

The EDL lists the order in which to playback the segments.EDL:Segment 1Segment 3Segment 3Segment 1Segment 2

EDL:Segment 1Segment 3Segment 3Segment 1Segment 2

The EDL tells the computer where to look on the disc for the next sample

When played back the complete section looks like this:

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Musical notationMusical notation

• Computers can be useful for transcribing music into musical notation and then laser printing it ready for musicians

• There are a number of music DTP (Desk Top Publishing) packages currently available that provide composers precise control over placement of musical symbols– e.g. Finale (see http://www.codamusic.com/)

• Professional MIDI sequencers usually provide notation facilities, e.g. Cakewalk Pro Audio, but these may not be suitable for all types of performance

• Notation editors provide cut-and-paste facilities for music much like word processors do for text

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Musical notationMusical notationCakewalk Pro AudioCakewalk Pro Audio

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Algorithmic composersAlgorithmic composers

• An algorithmic composer produces or composes music via algorithms– Mathematical or procedural representation of some human

activity– Some can require little or no human intervention– Early algorithmic composers made very electronic and non-

human type music

• Modern versions can be used to create standard MIDI files in a number of modern styles– e.g. Rock, Dance, Blues, Jazz, Classical, etc.

• They produce music based on rules that capture how a real musician would play the music in a given style– Can sound repetitive if the algorithm is too simple– Some packages introduce randomness or AI to improve the

performance quality

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Example algorithmic composerExample algorithmic composerJAMMER Hit SessionJAMMER Hit Session

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Quick TestQuick Test(To be done in the lab)(To be done in the lab)

• Open the three Cakewalk files in the following directory:– L:cd1011\examples\lecture9\– The files are called mystery1.wrk, mystery2.wrk

and mystery3.wrk

• Decide whether each of these performances was:– A) Created by human composer?– B) Created by an algorithmic composer?

• What evidence makes you think your answer is correct?

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SummarySummary

• MIDI and digital audio can be put to a number of uses

• Each has its own pros and cons: know them!• Examples of applications of computer audio:

– Direct-to-disk recording– Notation– Algorithmic composers

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Next lecture...Next lecture...

• We will look at some of the techniques employed to deliver digital audio and MIDI data over the Internet (essentially a low bandwidth medium)– Streaming data over a network– Real Audio (RA)– Microsoft Active Streaming Format (ASF)– Rich Music Format (RMF)