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Physics 1251 The Science and Technology of Musical Sound Unit 4 Session 42 MWF Computer Music Physics 1251 Unit 4 Session 41 Computer Music Please react to the following comment: “the use of computers stifles musical creativity.” Physics 1251 Unit 4 Session 41 Computer Music

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physics 1251 unit 4 session 41 computer music
Physics 1251 Unit 4 Session 41 Computer Music

Please react to the following comment:

“the use of computers stifles musical creativity.”

physics 1251 unit 4 session 41 computer music3
Physics 1251 Unit 4 Session 41 Computer Music

1′ Lecture:

  • MIDI provides a means for a computer to control several musical instruments in an interactive way.
  • Software is available that permits notation and composition editing.
  • Modern microelectronic is fast enough to permit real time digital signal processing.
  • Transmission of digital audio data requires compression schemes such as MP-3.
physics 1251 unit 4 session 41 computer music4
Physics 1251 Unit 4 Session 41 Computer Music

“A passion for music and a desire to push its boundaries are recurring themes at the Computer Music Center.”

David Jameson

Manager, Computer Music Center

IBM Watson Research Center

www.research.ibm.com/mathsci/cmc/do_lamentations1.htm

Lamentation for Jerusalem

For solo Saxophone and DMIX

By Daniel V. Oppenheim

physics 1251 unit 4 session 41 computer music5
Physics 1251 Unit 4 Session 41 Computer Music

Interactive MIDI permit novel sounds and a rich tonal palette.

Microtonal Music (scales not tuned in half steps) are facilitated by computer and MIDI sequencers.

Cf: http://home.att.net/~microtonal/

physics 1251 unit 4 session 41 computer music6
Physics 1251 Unit 4 Session 41 Computer Music

Software Music editors assist manuscript production and editing.

physics 1251 unit 4 session 41 computer music7
Physics 1251 Unit 4 Session 41 Computer Music

Demonstration:

Finale 2002

©2001 Coda Music Technology, Inc.

physics 1251 unit 4 session 41 computer music8
Physics 1251 Unit 4 Session 41 Computer Music

Sound Cards are the “ears” and “voices” of the minicomputer.

Speaker jacks

DAC

Mic jack

ADC

physics 1251 unit 4 session 41 computer music9
Physics 1251 Unit 4 Session 41 Computer Music

Microelectronics is now fast enough to permit real time digital signal processing (DSP).

80/20Dolby Noise Reduction:

A noise reduction technique in which the gain of the system automatically changes to maximize the signal-to-noise S/N ratio.

physics 1251 unit 4 session 41 computer music10

TM

Physics 1251 Unit 4 Session 41 Computer Music

Signal Processing--Dolby

  • Dolby Noise Reduction Scheme:
  • During loud portions music masks noise; S/N large.
  • During soft potions increase gain to record with larger S/N.
  • Playback with appropriate gain. S/N is better than before.

Ray Dolby Founder Dolby Digital

physics 1251 unit 4 session 41 computer music11
Physics 1251 Unit 4 Session 41 Computer Music

Digital Signal Processing (DSP):

80/20Fast Fourier Transform (FFT)

An efficient algorithm (method of doing arithmetic) in which a waveform is changed into its vibration recipe.

  • Advantages:
  • Reduction in data set size
  • Opportunity for processing
physics 1251 unit 4 session 41 computer music12
Physics 1251 Unit 4 Session 41 Computer Music

Fourier Transform

Waveform

Vibration (harmonic) Recipe

FFT

physics 1251 unit 4 session 41 computer music13

Original Frequency Spectrum

Low Pass Filter

Processed Spectrum

Physics 1251 Unit 4 Session 41 Computer Music

Digital Filters

Filters are arithmetic operators that increase or decrease the amplitude of the frequency components in the frequency spectrum (vibration recipe).

Noise reduced

Frequency

physics 1251 unit 4 session 41 computer music14
Physics 1251 Unit 4 Session 41 Computer Music

Data Compression and MP-3

  • Bit rate = word length x baud rate
  • Bit rate for CD = 32 bit x 44.1 kHz > 1.4 MHz
  • Storage requirements for 60 minutes of CD audio > 5 Gigabits.
  • To “down load” CD over modem line (~28 kbits/sec) requires nearly an hour per minute of audio!
  • Need data Compression.
physics 1251 unit 4 session 41 computer music15
Physics 1251 Unit 4 Session 41 Computer Music

80/20Audio Data Compression:

The technique of representing the essential information required to reconstruct an audio signal from an abbreviated or compressed data set.

physics 1251 unit 4 session 41 computer music16
Physics 1251 Unit 4 Session 41 Computer Music

MP-3

  • Based on MPEG (Motion Picture Experts Group) protocols.
  • Is a three layer compression scheme.
  • Uses knowledge from psycho-acoustics.
  • The data send is 10x t0 14x compressed.
  • The reconstructed audio file is not identical to the original, yet sounds indistinguishable from the original.
physics 1251 unit 4 session 41 computer music17

Buffer

MP-3

Filter

Bank

FFT

Physics 1251 Unit 4 Session 41 Computer Music

MP-3 Scheme

(3) Huffman coded

(1) Transformed

(2) Masked

physics 1251 unit 4 session 41 computer music18
Physics 1251 Unit 4 Session 41 Computer Music

Masking Filter

  • Relies on psychoacoustic phenomenon of masking.
  • Masking: a louder sound makes a simultaneous softer nearby frequency inaudible.
  • Concept: if frequency is inaudible, eliminate it with digital filter.
physics 1251 unit 4 session 41 computer music19
Physics 1251 Unit 4 Session 41 Computer Music

Masking Filter

LOG(Amplitude)

LOG(Frequency)

physics 1251 unit 4 session 41 computer music20
Physics 1251 Unit 4 Session 41 Computer Music

Summary:

  • MIDI permits computer control of electronic instruments.
  • Music Editor software aids the composer/arranger and can even “compose.”
  • DSP manipulates digital data using binary arithmetic.
  • MP-3 compresses the audio signal information.