Modulation Synthesis and Waveshaping
Lecture Slides
A series of gif images of the lecture slides... (only accesible from within Stanford University)
Modulation Synthesis
- short description of linear and non-linear systems
Ring Modulation
Amplitude Modulation
Frequency Modulation
Examples
- A very simple ring modulation instrument (ringmod.ins)
- A very simple ring modulation instrument with wavetable oscillators (ringmodw.ins)
- A very simple amplitude modulation instrument (ampmod.ins)
- A very simple amplitude modulation instrument with wavetable oscillators (ampmodw.ins)
- A very simple frequency modulation instrument (fmmod.ins)
Here are a bunch of fm instruments, mostly coming from the clm area ("/usr/ccrma/lisp/src/clm"). You should explore, there's a wealth of information and examples hiding there...
The eternal "fm bell". Here is the header of the instrument and a short description of its parameters:
(definstrument fm-bell (start-time duration frequency amplitude
amp-env index-env index
&optional (degree 0.0)
(distance 1.0)
(reverb-amount 0.005))
Mandatory parameters
- start-time
- starting time in seconds
- duration
- duration of the note in seconds
- frequency
- frequency of the note in Hertz
- amplitude
- amplitude of the note (between 0 and 1)
- amp-env
- amplitude envelope. A list of time-value coordinates that determines the evolution of loudness over time. The time values are relative and are scaled to the duration of the note (for example I usually use a time axis that stretches between 0 and 1).
- index-env
- modulation index envelope. A list of time-value coordinates that determines the evolution of modulation index over time. The modulation index controls the "brightness" of the sound (the higher the index the brighter the resulting sound).
- index
- modulation index. The scaler for the index envelope.
Optional parameters
- 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 random with-sound's
doesn't sound like a bell...
(with-sound()(fm-bell 0 4 440 0.1
'(0 0 0.05 1 0.2 0.4 0.8 0.2 1 0)
'(0 0 0.02 1 0.2 0.2 0.8 0.1 1 0)
1))
so let's tweak envelopes a bit...
(with-sound()(fm-bell 0 4 440 0.1
'(0 0 0.002 1 0.2 0.4 0.8 0.2 1 0)
'(0 0 0.001 1 0.1 0.08 0.8 0.01 1 0)
1))
maybe try a duller bell?
(with-sound()(fm-bell 0 4 440 0.1
'(0 0 0.002 1 0.2 0.4 0.8 0.2 1 0)
'(0 0 0.001 1 0.1 0.08 0.8 0.01 1 0)
0.3))
but with a different envelope and a lower frequency it's not a bell any longer... (but sounds like the typical fm wow)
(with-sound()(fm-bell 0 4 78 0.1
'(0 0 0.3 1 0.4 0.9 0.8 0.2 1 0)
'(0 0 0.35 1 0.38 0.9 0.8 0.01 1 0)
0.7))
A drum simulation. Here is the header of the instrument and a short description of its parameters:
(definstrument fm-drum (start-time duration frequency amplitude index
&optional
(high nil)
(degree 0.0)
(distance 1.0)
(reverb-amount 0.01))
Mandatory parameters
- start-time
- duration
- frequency
- amplitude
- index
- modulation index.
Optional parameters
- high
- "t" introduces an upwards glissando in the end of the note (the glissando function is a constant hardwired into the instrument, it could be made a parameter, of course).
- degree
- distance
- reverb-amount
Some example with-sound's
(with-sound ()
(fm-drum 0 1.5 55 .3 5 nil)
(fm-drum 2 1.5 66 .3 4 t))
A very nice gong simulation. Here is the header of the instrument and a short description of its parameters:
(definstrument gong (start-time duration frequency amplitude
&key
(degree 0.0)
(distance 1.0)
(reverb-amount 0.005))
Mandatory parameters
- start-time
- duration
- frequency
- amplitude
Optional parameters
- degree
- distance
- reverb-amount
Some example with-sound's
(with-sound () (gong 0 3 261.61 .6))
A generic and vey versatile fm instrument created by Bill Schottstaedt. A nice example of multipurpose coding. Almost everything has reasonable defaults but can be changed. If you examine the code you'll see another feature common to good instruments. The key parameters are defaulted to the value of special (global) variables. That opens the possibility of globally changing the behaviour of a bunch of notes by just encasing them in a "let" with redefinitions of those global variables. Here is the header of the instrument and a short description of its parameters (which has plenty off):
(definstrument fm-violin
(startime dur frequency amplitude &key
(fm-index fm-violin-fm-index)
(amp-env fm-violin-amp-env)
(periodic-vibrato-rate fm-violin-periodic-vibrato-rate)
(random-vibrato-rate fm-violin-random-vibrato-rate)
(periodic-vibrato-amplitude fm-violin-periodic-vibrato-amplitude)
(random-vibrato-amplitude fm-violin-random-vibrato-amplitude)
(noise-amount fm-violin-noise-amount)
(ind-noise-freq fm-violin-ind-noise-freq)
(ind-noise-amount fm-violin-ind-noise-amount)
(amp-noise-freq fm-violin-amp-noise-freq)
(amp-noise-amount fm-violin-amp-noise-amount)
(noise-freq fm-violin-noise-freq)
(gliss-env fm-violin-gliss-env)
(glissando-amount fm-violin-glissando-amount)
(fm1-env fm-violin-fm1-env)
(fm2-env fm-violin-fm2-env)
(fm3-env fm-violin-fm3-env)
(fm1-rat fm-violin-fm1-rat)
(fm2-rat fm-violin-fm2-rat)
(fm3-rat fm-violin-fm3-rat)
(fm1-index fm-violin-index1)
(fm2-index fm-violin-index2)
(fm3-index fm-violin-index3)
(base fm-violin-base)
(frobber fm-violin-frobber)
(reverb-amount fm-violin-reverb-amount)
(index-type fm-violin-index-type)
(degree nil)
(distance 1.0)
(no-waveshaping nil)
(denoise fm-violin-denoise)
(denoise-dur .1) ;used to be .5
(denoise-amp .005)
&allow-other-keys)
Mandatory parameters
- startime
- dur
- frequency
- amplitude
Optional parameters
- fm-violin-fm-index 1.0
- overall modulation index.
- fm-violin-amp-env '(0 0 25 1 75 1 100 0)
- amplitude envelope.
- fm-violin-periodic-vibrato-rate 5.0
- periodic vibrato frequency (periodic vibrato is a triangular wave).
- fm-violin-random-vibrato-rate 16.0
- random vibrato rate (random noise added to the vibrato).
- fm-violin-periodic-vibrato-amplitude 0.0025
- amplitude of the periodic vibrato.
- fm-violin-random-vibrato-amplitude 0.005
- amplitude of the random vibrato.
- fm-violin-noise-amount 0.0
- add index and amplitude noise (internal movement of the sound).
- fm-violin-noise-freq 1000.0
- bandwidth of the index and amplitude noise.
- fm-violin-ind-noise-amount 0.0
- index noise amount
- fm-violin-ind-noise-freq 10.0
- bandwidth of index noise.
- fm-violin-amp-noise-amount 0.0
- amplitude noise amount
- fm-violin-amp-noise-freq 20.0
- bandwidth of amplitude noise.
- fm-violin-gliss-env '(0 0 100 0)
- glissando envelope (pitch envelope)
- fm-violin-glissando-amount 0.0
- scaler for the pitch envelope.
- fm-violin-fm1-env '(0 1 25 .4 75 .6 100 0)
- index envelope for first modulator
- fm-violin-fm2-env fm-violin-fm1-env
- fm-violin-fm3-env fm-violin-fm1-env
- fm-violin-fm1-rat 1.0
- modulator / carrier frequency ratio for first modulator.
- fm-violin-fm2-rat 3.0
- fm-violin-fm3-rat 4.0
- fm-violin-base nil
- kind of interpolation to be done between envelope points.
- fm-violin-frobber nil
- fm-violin-reverb-amount 0.01
- reverberation amount.
- fm-violin-index-type :violin
- fm-violin-denoise nil
- whether to try to reduce quantization noise in envelopes.
- fm-violin-index1 nil
- modulation index for the first modulator.
- fm-violin-index2 nil
- fm-violin-index3 nil
Some example with-sound's
For a compilation of examples on how the fm-violin can sound load the /usr/ccrma/lisp/src/clm/fmviolin.clm file. Here's the 20 Mbyte soundfile (fmviolin.snd) created by loading the file (will save you some time since the sounds take a while to get compiled). Please be aware that for this example to work you will have to compile and load a reverberator (jcrev.ins). If you want to play with the lisp code inside I strongly suggest you take apart the file and create a small with-sound for each example you are interested in... the whole soundfile is almost 20Mbytes long.
Chowning's fm voice instrument.
(definstrument fm-voice (beg dur pitch amp
vowel-1 sex-1 ampfun1 ampfun2 ampfun3
indxfun skewfun vibfun ranfun
dis pcrev deg vibscl pcran skewscl ranpower
glissfun glissat glissdc glissamt at1 at2 dc1 dc2)
Some example with-sound's
(let ((ampf '(0 0 1 1 2 1 3 0)))
(with-sound (:wait t)
(fm-voice 0 1 300 .8 3 1 ampf ampf ampf ampf ampf ampf ampf 1 0 0 .25 1 .01 0 ampf .1 .1 0 .1 .1 .1 .1)))
Real Time CLM instruments
"ringo-forever" is the name of a simple real time clm instrument that lets you control the frequencies of two sine wave oscillators in real time. The instrument can be "plugged" into a "tester" (another real time instrument) to display the waveform and fourier transform in real time.
ringo.cl is the ring modulation instrument definition and tester.cl is the "tester" instrument that will display the waveform and fft. There are several steps to be done (and none must be missed to start the real time instrument:
- compile and load both "tester.cl" (has to be compiled first!) and then "ringo.cl". This will create two separate programs. The instrument itself (which runs within lisp) and the Motif/X graphical interface program that will be used to control the instrument in real time (which can be run from a terminal).
- if this is the first time you run a real time instrument since you started lisp type "(open-controls 2048)" into the lisp interpreter. This will create the shared memory that is used by both lisp and the c program.
- start the "tester" program. Normally the program will be compiled into your home directory. So go to a terminal, type "cd" to make sure you are in your home directory and then start the tester by typing "tester_lnx &". You'll get a graphical interface window with two panes (waveform and spectrum displays).
- start the "ringo" program. This is the graphical interface for the "ringo-forever" real time instrument. Same as before, go to your home directory and type "ringo &" to start it.
- make sure both programs have the on/off button in the "on" position.
- go to the lisp interface and start the real time instrument by typing "(with-psound()(tester)(ringo-forever t))"... and off you go!!
- to stop the instrument: click the on/off buttons in both the tester and ringo graphical interfaces to the "off" position. The real time instrument will automatically exit its sample generation loop.
- before quitting lisp remember to deallocate the shared memory by doing a "(close-controls)".
To probe further
Create a "Modulation Song" using the example instruments (or custom versions of them, needless to say adding envelopes to control parameters would make most of them much more interesting...). Plug in parameters and experiment with them. Experiment with different amplitude envelopes (for example: create percussive attacks). Doesn't have to be very long, 1 minute tops! Have fun!