Upcoming:
Nov-8 convolution, note lists
Nov-13 John Chowing on size constancy, loudness, spatialization, reverberation
Nov-15 Parag extsnd.html, extended menu, calling menu controls from scripts
Nov-20 map-chans, non-linear (active excitation for clarinets, flutes, bugles)
Nov-22 --no class--
Nov-27 non-linear (passive distortion for gongs, thrash metal guitars)
Nov-29 envelopes
Nov-8

Reading: chapters 9 - 11

Topics: tuning systems, convolution

A programming challenge to do at beginning of class: using scheme...

What is the frequency difference between a Perfect 5th (3/2) and an equal-tempered 5th, for the second above middle-C?

guile> (define a 440.0) ; that's the note `A'
guile> (define p5 1.5)
guile> (* a p5) ; the note `E'
660.0
; define et5 ratio by calculating 7 semitone steps of 2 ^ (1/12), ... ie. 2 ^ (7/12)
; use expt procedure
(define et5 (expt 2 (/ 7 12)))

; then do this for the answer

guile> (- (* a p5) (* a et5))

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What is the frequency difference between a Perfect 5th one time around the cycle of fifths (transposed down) and a Perfect 5th?

guile> (define cf5 (expt p5 13))
guile> (define semitones (* 7 13))
guile> (/ semitones 12)  ; to get number of octaves
7
guile> (expt 2 7) ; so tranpose down the 13th p5 to the same octave
128
guile> (- (* a p5) (* a (/ cf5 128)))

Convolution
 

Some web links to impulse responses and related projects in recording and auditorium work.

 http://orpheus.tamu.edu/fredrics/impulse.html

 http://www.cs.princeton.edu/~prc/ism98fin.pdf
 http://pcangelo.eng.unipr.it/Public/Papers/113-ICA98.PDF
http://www-sigproc.eng.cam.ac.uk/~jrh1008/Resources/Links/ImpulseResponses.html
 

Impulse response sound files are convolved with source material insound files that are to be reverberated or filtered. The first example in convolve.scm creates a click and convolves it with a bird call. The result is the bird call... that's because the single click creates a single copy of the source. The second example echoes the click once, and when that is convolved it creates two overlapping copies of the bird call, as if it were echoed itself.