The Synthesizer

  This could refer to PC cards, like the Roland GS SCD-15 daughtercard, or the Yamaha XG daughtercard, or one of the various sound cards, or a module, or a keyboard synthesizer (with just a simple interface to a PC). Or the synthesizer could be entirely a software program - a virtual synthesizer, such as that which emulates the Roland GS, or the Yamaha XG, or others.

  While not the first, an analog synth, the modular Moog, seems the first to have been introduced into pop music and pop culture. These early synths were much more limited, obviously (and of course bulkier) than today. Notes were generated with voltage oscillators, which because of limitations, have given way to digital oscillators since. These generate the 'tone', the note, the pitch itself. Filters, of various sorts - modulators, amps, waveshapers, whatever - are used to modify parts of the note. A note is struck, the basic pitch generated by this digital oscillator, according to the audio model of ADSR - attack, decay, sustain, and release - each of these four parts of a note can be tweaked and modified. The result, with either sort of oscillator, was a synthy sounding kind of wave, with a 'warmth', or a deep buzzy bass, or whatever seemed appealing. [In fact, even in the modern virtual synths, the same sort of convention will be used, and SysEx and other MIDI commands will refer to the DCO (digitally controlled oscillator), attack, release values, TVF and TVA and so on.]

  In the early 1980s, Yamaha came up with a twist on the oscillator method. This would be the F(requency) M(odulation) synthesis, in one form or another, which is one oscillator being filtered by other oscillators, and which is essentially the rather tinny and annoying sort of sound one finds on the 'card-the-computer-came-with', sort of sound card. It's some variation of FM synthesis 'crammed' onto a PC board (which you'll see referred to as, perhaps - OPL-3).

  The only useable and suitable sort of synthesized instrument now, however, would be some sort of wavetable synthesis; however picky some might be over the definition of, wave table, I refer here to sampled sounds. There may be some who swear even by the old voltage oscillator synths, for techno/dance/disco music. But that's because they want a synth to sound like a synth, not a piccolo or distortion guitar; and of course those old synths wouldn't necessarily even be MIDI compatible. In whatever is generally called, wavetable synthesis, a sample of an instrument is taken, with certain acoustics, and so on, so that when a note is triggered from MIDI, the synth will play the part, but best within a certain range of notes, as if someone were really playing the instrument. That's possible only because the wavetable produces such a believable and realistic sound, so that it doesn't sound like a synthesizer, if you don't want it to sound like one (it will still include some standard synth generated waves - saw wave, square wave, and like that). But as it is one aspect of the instrument, being played in a certain way, it really, ultimately, can't capture all the subtle shades and variation in sound that one gets when playing the instrument, itself. But it's close; sometimes more so than other times.

  The Roland GS synths come in all sorts. Some older ones play only a few channels and notes at a time. But more recent synths often exceed (like the XG) 24 notes polyphony (which is supposed to be a General MIDI standard), and have 600 (e.g. the 'super GS' SC-88 Pro) or so patches/instruments built in (also like the Yamaha XG). The PC daughtercard, the Roland SCD-15 (SCB-55), has 354 instruments, and various effects, with a maximum polyphony of 28 simultaneous notes, for all 16 channels. Roland's 'soft' or virtual synths, which incorporate the SCD-15 (or at least the SC-55), as it were, now go far beyond that, and are restricted only by the processing power of your computer.

  As noted above, there are certain ways of generating basic tone, but there are also certain ways of sampling and producing wave table instruments. Not all synths seem to have the same 'flavor', with their built in instruments, and particularly as one goes back in time with changes in synthesis methods. One synth might play one sort of song well, another might be best for another type. I've mentioned elsewhere, for example, that the Roland synths seem to have very dirty, growling sort of guitar samples, but not the XG. So the Roland works for hard rock, and heavy metal MIDIs. But the smoother, softer electric guitars of the XG might lend themselves more to softer, more 'airy' sort of guitar solos (say, Hendrix' somewhat obscure, Goin Country). It would just all depend. In fact, from what few synths I've heard, a decent distortion guitar, and a decent overdrive guitar in the low octaves, is not something that is so common, outside of the Roland GS. And this also suggests that the idea of sampling your own sounds, which might be unavoidable for people on certain projects, is not a trivial sort of thing; and suggests to me the difficulty of, for example, designing a decent true type font (whereas anyone can try, few might really succeed). The number of hardware synth modules, keyboards, and whatever, and now soft(ware) synthesizers might also suggest a lot of possibilities, and a lot of different sounds given the exact same MIDI (which also something of a real problem, as I'm forced to discuss, myself.

  Here, then, is a little more detail on various sorts of synthesizers.