Transcript Computer Music

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
1′ Lecture:
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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 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 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 Music
Software Music editors assist manuscript
production and editing.
Physics 1251
Unit 4 Session 41
Computer Music
Demonstration:
Finale 2002
©2001 Coda Music Technology, Inc.
Physics 1251
Unit 4 Session 41
Computer Music
Sound Cards are the “ears” and “voices”
of the minicomputer.
DAC
ADC
Speaker jacks
Mic jack
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 Music
Signal Processing--Dolby
TM
Dolby Noise Reduction Scheme:
(1) During loud portions music
masks noise; S/N large.
(2) During soft potions increase
gain to record with larger S/N.
(3) Playback with appropriate
gain. S/N is better than
before.
Ray Dolby
Founder
Dolby Digital
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 Music
Fourier Transform
Waveform
Vibration (harmonic)
Recipe
FFT
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).
Original Frequency Spectrum
Low Pass Filter
Processed Spectrum
Noise reduced
Frequency
Physics 1251
Unit 4 Session 41
Computer Music
Data Compression and MP-3
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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
80/20Audio
Unit 4 Session 41
Computer Music
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 Music
MP-3
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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 Music
MP-3 Scheme
Buffer
FFT
(1) Transformed
(3) Huffman coded
MP-3
Filter
Bank
(2) Masked
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 Music
LOG(Amplitude)
Masking Filter
LOG(Frequency)
Physics 1251
Unit 4 Session 41
Computer Music
Summary:
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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.