Oct-28
Stations for Wave study and visualization, cont'd:
Digression into using an abacus as an effects processor
Following the train of thought involving sound excitation, echoes and resonance, digital filters can be illustrated. We saw long delays create echoes and shorter delays create pitched resonances. The shortest delays can be used to create filtering effects like the tone controls on an amplifier.
Review:
The
outdoor clapping experiment used Snd to measure the speed of sound
between a mic and a nearby whiteboard surface by recording FIR
reflections. The string and tube experiments recorded IIR reflections
in string velocity waves and air column pressure waves.
Numerical version of the same, diagrammed in a flow chart ala Pd:
Summary
filters don't add frequencies (as opposed to modulation or distortion)
filters change duration and spectral weighting
size from big to little: echo, pitch, eq, image pos.
sharpness (`Q') from high to low: string, tube (inverse of damping, e.g., strings have less damping, ring longer)
it's hard to find simple filters in nature, most are combinations, e.g., the tubes
Composition Featuring Sound Analysis and Processing
Jonathan Harvey, Mortuos Plango, Vivos Voco (1980)
Harvey, Jonathan (1981)
Mortuos plango, vivos voco: a
realization at IRCAM.
Computer music journal, vol.
V/4 (winter 1981), 22-24.
Reprinted in The music machine.
Cambridge, MA: Massachusetts Institute of Technology, 1989. p. 91-94.
filename of piece: /usr/ccrma/snd/pieces/harvey/mortuos.snd (in 4 channels)
filename of article: /usr/ccrma/snd/cc/220a/Harvey.pdf
HW4: Trackers for Interaction, Pd's “fiddle” object
Adding some complexity to real-time interaction, track pitch and amplitude of mic input signals.
Start with the simplest use of fiddle and your instrument's input and see how well it tracks.
Tracker etude: Use Pd to track an instrumentalist in real time, with the detected dimensions either processing their incoming sound as an effect, or creating a synthesized accompaniment. Explore a range of possible relationships. Compose the etude for solo instrument and include a second player in the role of Pd assistant (who follows scored instructions and manipulates your patch accordingly – from computer keyboard and / or mouse).
Programming a Pd tracker: Create a new Pd patch for tracking playing on a sawed-off piece of PVC pipe (with at least one tonehole). Use Pd's “fiddle” object as pitch and amplitude detectors to control plucked-string synthesis in real-time. In the last homework, changes to the algorithm and music were triggered from computer keyboard. This time, figure out a way to have that happen based on the signal from the mic. E.g., when you hit a special note, something about the music changes. Here's a version of a plucked-string synthesis to start with.
Documentation mooched from Miller Puckette's book-in-progress on Pd: http://crca.ucsd.edu/~msp/techniques/latest/book-html/book.html
And the specific section mentioning use of “fiddle” http://crca.ucsd.edu/~msp/techniques/latest/book-html/node77.html
This graphic is from last year's class – shows a 2-tone PVC flute being tracked in amplitude and pitch by simple algorithms (not nearly as nice as the techniques used in fiddle).
