dr_d@sftig.UUCP (D.Donahue) (09/16/85)
> > - 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). > > Sunil > > UUCP: ...{harvard, seismo, ut-sally, sri-iu, ihnp4!packard}!topaz!mohan > ARPA: Mohan@RUTGERS Sunil, FM perpetuates the ability to specify time/frequency variant modulation co-efficients. These co-efficients, if I remember correctly, specify freq- uencies at which a sounds energy is greatest along with an associated range over which the energy is distributed. During time, the frequencies change as well as the range which modify the harmonic content of a given sound in time. It may have been an oversite, but maybe not: There is not such thing as a "Volume Envelop". Volume is a subjective term which really should have no place in a technically elightened persons vernacular. Most people realize that what you were refering to was of course an Amplitude Envelop. In any case, the proper technical term for an increase in sound energy is GAIN NOT VOLUME. I am not picking on you Sunil, this is a mistake most everyone makes. It is in fact, just a technical detail, but worth the time to make the distinction. The qualitative content of the remark is not significantly diminished, however. FM is simply a process, a means with which a sounds overtone content can be modulated, thus updated dynamically over time WITH GREAT EASE. FM DOES NOT allow "a greater variety of overtone structure than traditional subtractive synthesis", it simply makes the creation and modification thereof much more simple for the same result. Any sound that can be had with FM can be had by implementing either the addative or subtractive synthesis techniques. Again, FM is a process with simply makes the generation of certain of "kinds" of sounds a much easier ordeal with generally much less equipment. This brings the discussion around to probable reasons why analog synths only have one voltage controlled resonance frequency modulator in their filter section: COST/performance. Comparatively and generally speaking, the cost of analog hardware is much more than the cost of digital hardware. The performance of an analog machine would only be marginally increased (from a manufactures point of view) by the addition of another or perhaps several VCRFMs while adding tangible hardware and development, thus retail costs. Douglas Donahue AT&T Information Systems attunix!dr_d