CMSHN1114/CMSCD1011 Introduction to Computer Audio

1. 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: d.england@livjm.ac.uk

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 Multimedia developer Sound engineer / producer Musician Sequencer Digital multitrack recorder Notation (DTP) Digital audio editor Patch editor / librarian Algorithmic composer

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 1 Segment 2 Segment 3 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 Each segment is marked (i.e. its start and end points are noted)

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 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

10. Musical notationCakewalk 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 composerJAMMER 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?

14. 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

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)