Lecture 6
More on filters, Vocoder, LPC, Granular Synthesis

Lecture Slides

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

More on filters

FIR and IIR filters, comparison and basic concepts. To ways to use filters: the vocoder and the LPC techniques.

Granular Synthesis

Overview of granular synthesis techniques.

Examples

Here's a simple granular synthesis instrument in clm (grani.ins).

Here is the header of the instrument and a short description of its parameters:

(definstrument grani (start-time duration amplitude file
		      &key
		      (amp-envelope '(0 0.3 1 0.7 1 1 0))
		      (grain-envelope '(0 0 0.3 1 0.7 1 1 0))
		      (grain-duration 0.1)
		      (grain-hop 0.2)
		      (grain-hop-spread 0.05)
		      (in-file-srate 1.0)
		      (in-file-start 0)
		      (in-file-hop 0.2)
		      (in-file-hop-spread 0.05)
		      (degree 45)
		      (distance 1)
		      (reverb-amount 0.01))

Mandatory parameters

start-time: starting time in seconds
duration: duration of the note in seconds
amplitude: amplitude of the note
file: the complete pathname of the soundfile you want to use as source material

Optional parameters

amp-envelope: amplitude envelope for the whole note
grain-envelope: amplitude envelope for an individual grain
grain-duration: duration of each individual grain
grain-hop: distance in seconds between grains (can be smaller than the grain-duration)
grain-hop-spread: maximum random component in seconds added to the grain-hop
in-file-srate: sample rate conversion factor for the input file
in-file-start: position in seconds in the input file where to start getting samples
in-file-hop: distance in seconds between starts of grains in the input file
in-file-hop-spread: random component added to the distance in seconds between starts of grains
degree: angle in degrees from where the sound is coming from in a stereo rendition. "0" is left and "90" is right; "45" is right in the middle of the stereo field.
distance: distance in feet from where the sound is coming from.
reverb-amount: amount of reverberation added to the sound. For this to work you must have a reverberator loaded and the with-sound call has to specify it.

Some examples...

Just a silly stuttering gong:

(with-sound()(grani 0 8 2 "/Web/Info/CCRMA/Courses/220a/Lectures/6/Sounds/small-gong.snd"))

Smaller grains:

(with-sound()(grani 0 8 2 "/Web/Info/CCRMA/Courses/220a/Lectures/6/Sounds/small-gong.snd" :grain-duration 0.06 :grain-hop 0.045 :grain-hop-spread 0.008 :in-file-hop 0.05 :in-file-hop-spread 0.001))

Smaller grains, downsampled by a 0.3x factor:

(with-sound(:statistics t)(grani 0 8 2 "/Web/Info/CCRMA/Courses/220a/Lectures/6/Sounds/small-gong.snd" :grain-duration 0.06 :grain-hop 0.045 :grain-hop-spread 0.008 :in-file-hop 0.05 :in-file-hop-spread 0.001 :in-file-srate 0.3))

Smaller grains, downsampled by a 0.3x factor. Note that we change the position were we start sampling the input file and create a big spread there so that we are actually jumping around randomly:

(with-sound(:statistics t)(grani 0 8 2 "/Web/Info/CCRMA/Courses/220a/Lectures/6/Sounds/small-gong.snd" :grain-duration 0.06 :grain-hop 0.07 :grain-hop-spread 0.04 :in-file-hop 0.05 :in-file-hop-spread 0.9 :in-file-srate 1.5 :in-file-start 2.6))

Three notes spread in the stereo field:

(with-sound(:channels 2 :statistics t)
(grani 0 8 4 "/Web/Info/CCRMA/Courses/220a/Lectures/6/Sounds/tubular-bell.snd" 
       :grain-duration 0.06 :grain-hop 0.05 :grain-hop-spread 0.02 
       :in-file-hop 0.05 :in-file-hop-spread 0.6 :in-file-srate 1 :in-file-start 2)
(grani 0 8 4 "/Web/Info/CCRMA/Courses/220a/Lectures/6/Sounds/tubular-bell.snd" 
       :grain-duration 0.08 :grain-hop 0.06 :grain-hop-spread 0.02 
       :in-file-hop 0.05 :in-file-hop-spread 0.3 :in-file-srate 1.1 :in-file-start 2.6 
       :degree 0)
(grani 0 8 4 "/Web/Info/CCRMA/Courses/220a/Lectures/6/Sounds/tubular-bell.snd" 
       :grain-duration 0.05 :grain-hop 0.03 :grain-hop-spread 0.02 
       :in-file-hop 0.05 :in-file-hop-spread 0.5 :in-file-srate 0.9 :in-file-start 1.6 
       :degree 90))

Try replacing the turkish-cymbal-1.snd soundfile instead of the tubular-bell...

Assignment

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 "/Web/Info/CCRMA/Courses/220a/Lectures/6/Sounds/small-gong.snd", a small cowbell in the same directory, file name "cencerros-1.snd", a cymball and a tubular bell... Have fun!

Lecture 6 More on filters, Vocoder, LPC, Granular Synthesis