CMSHN1114CMSCD1011 Introduction to Computer Audio

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CMSHN1114/CMSCD1011 Introduction to Computer Audio

• Lecture 9 Computer audio applications
• Dr David England
• School of Computing and Mathematical Sciences
• http//java.cms.livjm.ac.uk/homepage/staff/cmsdeng
  l/Teaching/cmscd1011.html
• Email d.england_at_livjm.ac.uk

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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 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 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 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 applications
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Direct-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 Lists
Each segment is marked (i.e. its start and end
points are noted)
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Musical 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 notationCakewalk Pro Audio
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Algorithmic 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 composerJAMMER Hit Session
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Quick Test(To be done in the lab)

• Open the three Cakewalk files in the following
  directory
• Lcd1011\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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Summary

• 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...

• 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)