csdf@mit-vax.UUCP (Charles Forsythe) (09/12/85)
I can't take it anymore! I can't wait a year to take Bose's accoustics course to learn this. What, exactly *is* FM sound synthesis and why is it so great? Somebody out there must know! I expect that I am simply missing something obvious because I do know: 1) What a Fourrier transform is. 2) What a Z-transform is 3) What FM is (as a process) 4) Just about any other "signal processing" jargon. Unfortunately, MIT loves theory but not application, so they never bothered to explain how FM could be used to create amazing synth effects and such. I appreciete any answers anyone cares to send, and if anybody else has been silently ignorant, I will be happy to summarize to the net. -- Charles Forsythe CSDF@MIT-VAX "What? With her?" -Adam from _The_Book_of_Genesis_
mohan@topaz.RUTGERS.EDU (Sunil Mohan) (09/13/85)
> I can't take it anymore! I can't wait a year to take Bose's accoustics > course to learn this. What, exactly *is* FM sound synthesis and why is > it so great? Somebody out there must know! I expect that I am simply > missing something obvious because I do know: An excellent reference would be John Chowning's article on FM for music. This was republished in the Computer Music Journal (I forget the issue, but pre 1980 I think), and also in the book "Foundations Of Computer Music", both published by MIT press. And you do not need Bose's Accoustics course. I think there are two main reasons why FM is "so great" (I personally am not too impressed, but then the kinds of sounds I need are not that readily, or at least easily reproducible in FM): - Something to do with its being digital allows it to produce nice "clean" and strident sounds, which can easily ride over other instruments, making it good for leads in pop/rock. - The ability to specify time-varying modulation ratios allows the overtones structure (timbre) of a sound to vary over its Volume Envelope, and with note dynamics. This is a prime requirement for duplicating natural accoustic timbres. All FM instruments allow additive synthesis, which is inherently more flexible than subtractive by allowing arbitrary overtone structures. Note that the voluble proponent of additive synthesis, Wendy Carlos, uses individual oscillators for the lower overtones, resorting to FM only at the upper reaches. This brings me to a burning question: Why do all Analog synths I have seen (inc the mighty MATRIX-12) have only one Voltage Controlled Resonance Frequency in their filter sections ? Wouldn't having more than one add flexibility ? Also FM allows a greater variety of overtone structures (as in the shape of the locus of amplitudes of overtones) than traditional subtractive synthesis (see flame above). Has anyone experimented with any of the following: - More than one VCF on a voice ? - Adding VCFs to a DX7 or sthg similar ? - Using a choruser/whatever on a DX7 to try to get "thick analog" sounds ? -- _ Sunil UUCP: ...{harvard, seismo, ut-sally, sri-iu, ihnp4!packard}!topaz!mohan ARPA: Mohan@RUTGERS
rlr@pyuxd.UUCP (Rich Rosen) (09/16/85)
> I can't take it anymore! I can't wait a year to take Bose's accoustics > course to learn this. What, exactly *is* FM sound synthesis and why is > it so great? Somebody out there must know! [CHARLES FORSYTHE] For a good summary of FM synthesis and its beginnings, read the paper by John Chowning (of Stanford's CCRMA) called "Synthesis of Complex Audio Spectra by Means of Frequency Modulation". It appeared originally in the Journal of the Audio Engineering Society (Vol. 21, No. 7, Sept. 1973), and it was reproduced in the second issue (Vol. 1, No. 2) of the Computer Music Journal. Those first few issues of CMJ are chock full of absolutely excellent theoretical articles about digital synthesis, simulation of acoustic instruments and motion of sound sources. I stopped subscribing during the course of volume four. Does anyone else out there still subscribe and have recommendations (or not) about the journal? (Charles, CMJ is published by MIT Press, or at least it was until recently. In the early days it was published out of Menlo Park CA, hence the early Stanford contributions.) -- "Wait a minute. '*WE*' decided??? *MY* best interests????" Rich Rosen ihnp4!pyuxd!rlr
aurenz@uiucuxc.Uiuc.ARPA (09/17/85)
> What, exactly *is* FM sound synthesis and why is it so great? > Somebody out there must know! I expect that I am simply > missing something obvious because I do know: > > 1) What a Fourrier transform is. > 2) What a Z-transform is > 3) What FM is (as a process) > 4) Just about any other "signal processing" jargon. If you understand FM as a process (e.g. as applied to radio communication), then you understand FM as a synthesis technique. All math is the same, only the operating parameters are different. For example: 1) In FM radio, the modulator signal is in the audio band (20-20Khz) and the carrier is around 100Mhz. With FM synthesis, both carrier AND modulator are in the audio band, and are generally related by small integer ratios (e.g. 2:1, 3:1 etc.) Non-integer ratios are also used to produce non-harmonic spectra (i.e. metal sounds). 2) In FM radio, the modulation index tends to stay constant; in FM synthesis this index varys with time. Doing this varys the spectra over time, which is what "real" and interesting sounds do. 3) So for simple simple case of sinusoidal modulation (one carrier one modulator): +-------+ | Mod | +-------+ | V +-------+ | Car | +-------+ | V Out you can use the standard bessel functions to compute the output spectra. Of course, when you stack your modulators the computation gets much trickier. The reason FM is "so great" is that it's a relatively cheap way to generate very complex spectra with relatively few parameters (as opposed to additive synth, which needs quite a lot). So in that respect, FM is a more "powerful" technique than additive synth. The drawback of FM is, as mentioned in (3), it's very difficult to transform between (parameters <-> spectra) for all but very simple cases. Hence the need for much heuristic knowledge of the behaviour of FM spectra. By contrast, in additive synthesis one can basically "lift" the necessary synth parameters from a 2d spectral plot. Well, that's enough hot air for now. Hope it helps! ----------------------------------------------------------- Scot Aurenz { ihnp4! pur-ee! } uiucdcs!uiucuxc!aurenz
aurenz@uiucuxc.Uiuc.ARPA (09/20/85)
> [KEVIN KARPLUS] > ...The balance between technical and musical articles seems > to have been lost a few years back. I don't know whether to attribute > this to the loss of John Strawn as an editor, or to the dearth of > people submitting technical articles. I don't know about the former, but it certainly isn't due to the QUANTITY of articles submitted to CMJ. When I talked with Mr. Curt Roads, the current editor, at this year's ICMC* he cofirmed that the lag time between an article's submission and publication is now about one YEAR (!), mainly due to the sheer number of articles to be processed. * International Computer Music Conference (Vancouver, BC) > If you (or someone you know) has been doing research in computer music, > I encourage you to submit an article to CMJ. I could use some more > good reading. Actually, if any of you live in the Boston/Cambridge vicinity, I think CMJ would perhaps appreciate a few more minds and hands for the task. And to those out there who are referees, etc. for CMJ: hey, what about this turnaround problem? Any suggestions? Scot Aurenz { ihnp4! pur-ee! } uiucdcs!uiucuxc!aurenz