Transcript Computer audio applications

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/cmsdengl/
Teaching/cmscd1011.html
Email: [email protected]
Introduction to Computer Audio
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In this session...
• We will look at the applications of computer audio
which are applicable to:
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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
Musician
Sound engineer / producer
Sequencer
Notation (DTP)
Patch editor / librarian
Multimedia
developer
Digital
multitrack
recorder
Digital audio editor
Algorithmic composer
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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
Original recording
Segment 1
Segment 2
Segment 3
Each segment is marked (i.e. its start and end points are noted)
EDL:
Segment 1
Segment 3
Segment 3
Segment 1
Segment 2
The EDL lists the order in which to playback the segments.
When played back the complete section looks like this:
The EDL tells the computer where to look on the disc for the next sample
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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 notation
Cakewalk 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 composer
JAMMER Hit Session
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Quick Test
(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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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)
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Streaming data over a network
Real Audio (RA)
Microsoft Active Streaming Format (ASF)
Rich Music Format (RMF)
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