1 CMSHN1114/CMSCD1011 Introduction to Computer Audio Lecture 9: Computer audio applications Dr David England School of Computing and Mathematical Sciences Teaching/cmscd1011.html

2 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

3 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...

4 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!

5 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

6 A taxonomy of computer audio applications Sequencer Notation (DTP) Patch editor / librarian Algorithmic composer Digital multitrack recorder Digital audio editor Musician Sound engineer / producer Multimedia developer

7 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

8 Edit Decision Lists Original recording Segment 1Segment 2Segment 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 1 Segment 3 Segment 1 Segment 2 EDL: Segment 1 Segment 3 Segment 1 Segment 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:

9 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 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

10 Musical notation Cakewalk Pro Audio

11 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

12 Example algorithmic composer JAMMER Hit Session

13 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?

14Summary 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

15 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)