Introduction into Digital Audio, Psychoacoustics and MSP.

This week we started working with audio signals in MSP.

We started the class reviewing some principles of digital audio (discrete time and audio in digital systems) and discussed some basic concepts, such as the Nyquist-Shannon theorem, the meaning of word size (or bit depth), vector sizes (audio buffer sizes), and looked at the path a sound wave takes from its physical production into the digital system and after being processed its conversion back into the physical world (see figure below).



We then started producing our first sound in MSP (using the [cycle~] object), used simple arithmetics [*~], [+~] for mixing and scaling signals, and introduced objects for routing audio ([selector~], [gate~]) and sending/receiving audio signals without patch cords ([send~]/[receive~]). We then produced our discussed the properties (time domain and frequency domain) of basic waveforms, namely sine wave, sawtooth, rectangle (or square), and different types of noises.

We then went on discussing perceptual characteristics of sound perception and psychoacoustics, such as pitch perception, and experimented with distorted and stretched/compressed harmonic spectra. Please find the weekly patches in the Download section. We then studied the phenomenon of the ‘virtual fundamental‘ or ‘Virtual Pitch‘ as termed by E. Terhardt.

We also discussed the effects of beating occurring with two tones with similar/close frequencies and the difference to the so-called binaural beats  where the tones do not interfere physically, but are summed by the brain in the olivary nucleus.

For next week, please download and install the CIRMMT Live Electronics Framework (CLEF) which you can download here . CLEF comes as a Max Package, i.e. a folder that you should copy “/Documents/Max/Packages” in your user directory. Inside the “clef” folder you will find a subfolder “documentation” containing the CLEF Quickstart guide which gives a quick intro into the environment. You will also find a folder “examples” containing the file “01-simpleproject.maxpat”. Please open this patch and verify if Max complains about any missing objects or throws any warnings/errors in the Max window.

As usual, you can find the weekly assignment on McGill’s myCourses page. This week it is a sound-design task, based on the perceptual principles described in J. Chowning’s  paper “Digital Sound Synthesis, Acoustics, and Perception: A Rich Intersection” (DaFX 2000).