Granular Synthesis and Sampling Rate Conversion

Lecture Slides

A series of gif images of the lecture slides... (only accesible from within Stanford University)

Granular Synthesis

Overview of granular synthesis techniques.


Here's a simple granular synthesis instrument in clm (for clm-2). Go to its own page for details but beware, that page has a pointer to a clm-1 version only of the instrument (but the docs apply to both versions)...

Here is the header of the instrument and a short description of its parameters (see the source code for the parameter defaults):

(definstrument grani 
    (start-time duration amplitude file
		(grains grani-grains)
		(amp-envelope grani-amp-envelope)
		(grain-envelope grani-grain-envelope)
		(grain-envelope-end grani-grain-envelope-end)
		(grain-envelope-transition grani-grain-envelope-transition)
		(grain-duration grani-grain-duration)
		(grain-duration-spread grani-grain-duration-spread)
		(grain-duration-limit grani-grain-duration-limit)
		(srate grani-srate)
		(srate-spread grani-srate-spread)
		(srate-linear grani-srate-linear)
		(srate-base grani-srate-base)
		(srate-error grani-srate-error)
		(grain-start grani-grain-start)
		(grain-start-spread grani-grain-start-spread)
		(grain-density grani-grain-density)
		(grain-density-spread grani-grain-density-spread)
		(reverb-amount grani-reverb-amount)
		(reverse grani-reverse)
		(where-to grani-where-to)
		(where-bins grani-where-bins)
		(grain-distance grani-grain-distance)
		(grain-distance-spread grani-grain-distance-spread)
		(grain-degree grani-grain-degree)
		(grain-degree-spread grani-grain-degree-spread))

Mandatory parameters

starting time in seconds
duration of the note in seconds
amplitude of the note
the complete pathname of the soundfile you want to use as source material for the grains

Some of the optional parameters

After the name of the parameter I specify the type of parameter. Most of the key parameters can be either numbers (for a constant value) or an envelope.

amp-envelope [envelope]
amplitude envelope for the whole note
grain-envelope [envelope]
amplitude envelope for each individual grain
grain-envelope-end [envelope or nil]
a second amplitude envelope for each individual grain. If specified, grain-envelope-transition can be used to interpolate between both envelopes over the duration of the note.
grain-envelope-transition [envelope]
interpolation envelope for the grain envelope (used only if grain-envelope-end has been specified).
grain-duration [number or envelope]
duration in seconds of each individual grain
grain-duration-spread [number or envelope]
random deviation from grain-duration
grain-duration-limit [number]
minimum duration in seconds of a grain
srate [number or envelope]
sample rate conversion factor. The value for each grain is either a constant if the parameter is a number or is determined by the value of the envelope at the point in time where the grain starts. The sample rate conversion factor is a constant within the grain. If not overriden by the sampling rate conversion factor is specified in semitones (positive values transpose the sound up and negative values transpose down).
srate-spread [number or envelope]
random deviation the value of srate
srate-linear [t or nil]
defines the type of envelope used for the sampling rate conversion factor:
nil (the default): "srate" is expressed in fractional semitones above or below the original sampling rate (0 = no change in sampling rate conversion). The exponential envelope is approximated by a linear segment representation. The error bounds of the approximation can be set by srate-error. The base of the exponential curve can be changed by srate-base.
t: "srate" is the linear sampling rate conversion factor (1 = no change in sampling rate).
srate-error [number]
error bound for the exponential conversion
srate-base [number]
base for the exponential conversion. "2" will express the envelope in octaves. "(expt 2 (/ 12)" will express the envelope in semitones.
grain-start [number or envelope]
point in the input file where the samples are going to be read from. "0" represents the start of the input soundfile, "1" represents the end. An envelope can be used to produce arbitrary mappings over time.
grain-start-spread [number or envelope]
random deviation from the value of grain-start.
grain-density [number or envelope]
number of grains per second that will be created.
grain-density-spread [number or envelope]
random deviation from the value of grain-density.
reverse [t or nil]
"t" means the input soundfile will be read backwards (each grain will read backwards but of course this is independent from grain-start, for example we could be advancing forwards in the file but reading the samples backwards).
reverb-amount [number]
amount of sound to be sent to the reverb output stream.
grain-distance [number or envelope]
distance to the listener position (for locsig)
grain-distance-spread [number or envelope]
random deviation from the value of grain-distance
grain-degree [number or envelope]
angular position (for locsig)
grain-degree-spread [number or envelope]
random deviation from the value of grain-degree
Some examples...

Here's the "one-cut" instrument, a soundfile mangling machine... (cut.ins). Here are some parameter examples you can paste into a with-sound.

Some loop macro examples

These are examples on the use of the common lisp "loop" macro that I created for the ccrma 220b class... they might be useful.

So here they are, keystroke by keystroke (including typos) "what the instructor typed in" guide to the loop macro and its use in (very coarse) control of clm instruments. Some comments were added to the code to make it clearer. You will need to compile and load the fm-violin instrument to make this examples work.

If you're slightly out of your mind you can actually look at the whole thing...

Here's a pointer to the Steele's Common Lisp book chapter on the loop macro

To probe further

Use the "grani" granular synthesis instrument for processing (ie: mangling) input soundfiles. Create some interesting transformations on the input. Make soundfiles sing and or sttttttutttter. There are some soundfiles available for use (or you can roll your own). You can find a small gong in "/usr/ccrma/web/html/workshops/linux2000/lectures/8a/sounds/small-gong.snd", a small cowbell in the same directory, file name "cencerros-1.snd", a cymbal and a tubular bell... Have fun!

©1997-2001 Fernando Lopez-Lezcano. All Rights Reserved.