FM synthesis, at its core, is not difficult to understand. Most people who know something about subtractive synthesis are familiar with the term “modulation”, and are aware of the effects of an LFO on an audio oscillator or a voltage-controlled filter. In FM synthesis, the “modulator” has the same effect on a “carrier” that an LFO has on an oscillator: it modulates the frequency. The difference here is that a modulator in an FM synthesizer usually modulates the carrier at such a high frequency that you can’t actually hear the modulation happening; instead the perceived effect being a change in the wave shape. Routing a sine wave carrier through a sine wave modulator results in a more complex waveform than a simple sine, and the frequency of that modulator, as well as the modulation amount, can result in different wave shapes. This is FM at its core, yet people continue to shy away from it because of its reputation of complexity. The reason why it has attained such infamy is most likely the Yamaha DX-7: it has six operators which are arrangeable in different algorithms to determine which operators (an operator in FM speak is basically a sine-wave oscillator with an amplitude envelope attached) act as carriers and which ones act as modulators, and which carriers are routed through which modulators. Obviously this is rather more complicated than simply having one carrier and one modulator, but when paired with the DX-7’s tiny LCD screen and confusing button interface, FM suddenly seems very cryptic and unfriendly. I had a similar experience during the time I owned a DX-7, and needless to say I didn’t own it for very long.
My relationship with FM became a healthy one when I stumbled across a little “toy” keyboard in a local guitar shop: a Yamaha PSS-480. The PSS-480 is one of those keyboards loaded with cheesy preset sounds like “E. Piano 1”, “Elec. Guitar”, “Bagpipe”, Harmonica”, and so on. It has the to-be-expected auto-accompaniment section with grainy sampled drums and silly reggae-tinged basslines and chord progressions. All the ingredients of a keyboard that you’d expect to find at a Toys ‘R’ Us circa 1988. Something most of the people buying these in the late twentieth century probably didn’t know was that it is, in fact, a two-operator FM synthesizer. The PSS-480 has only one carrier and one modulator, and with obviously no room to figure complex algorithms into the mix, altering the relationship between operators is decidedly less mind-numbing than it is on more complex FM machines like the DX-7. There are six buttons allowing users to select a parameter to edit. Tapping the button once will engage that parameter for Operator One (the modulator); tapping it a second time engaging the same parameter for Operator Two (the carrier). The parameters we have access to are as follows: “attack rate”; “decay rate”; “frequency”; “feedback level”; “modulation level”; and “total level”. With control over these parameters, we can change any of the ninety-nine preset sounds, transforming them from their silly, eighties “home keyboard” selves into strange, harmonically rich, sometimes even eerie, alien sounding FM voices; snarling, punchy basses; percussive blips or bell sounds. When you’re satisfied with what you’ve done to a sound, you can save it one of five slots dedicated to storing user patches, and call it back up simply by pressing the “bank” button you saved it to. The PSS-480 has five “effects” that can be applied to any sound: “vibrato”, “sustain”, “reverb” (don’t get excited about this one: it does the same thing as “sustain”, just more quietly); “portamento”, and “duet”. “Vibrato” is rather self-explanatory. If you don’t know what that does, sing a sustained note and press your finger rhythmically into your Adam’s apple. “Sustain” in this case lengthens the release time, “portamento” is an adjustable parameter that creates a slide between notes played on the keyboard; “duet” plays automatic harmonies with the key pressed in the “melody” section of the keyboard depending on which note is held in the “auto-accompaniment” section. That’s really all there is to the sound engine, so obviously you will reach the limit of sound creation much sooner than you will on a DX-7 or something similar. I actually like that about it, and I recommend it to anyone who wants to learn the basics of FM synthesis without the tedious algorithm system that frankly made me want to tear out my hair.
I want to take some time to discuss the actual sound quality of the PSS-480, as I find it to be charming. I have fond memories of playing MS-DOS games as a kid, and the sound that comes out of this synthesizer brings back the music from those games instantaneously. Most computers that ran MS-DOS back in the early 90s had AdLib or Sound Blaster sound cards in them, which were essentially FM synthesizers that took MIDI data from computer programs and spat out that data as music and sound effects. The component that breathed life into this era of computer game music was indeed an FM synthesizer chip made by Yamaha (if you’re interested, it’s called the “YM3812”), and that exact chip can be found inside other home keyboards of the late eighties: the PSS-470, PSR-12, and PSR-32, among several others. The chip inside the PSS-480 is not a YM3812, but a very similar one nonetheless. I’ve found that the actual YM3812 chip has a grainier, grittier sound and the one inside the PSS-480 is a bit cleaner (I suppose what I mean by that is “having less character”), but I prefer the 480 for its ability to save user presets and a wider range of parameters for editing the sounds. The YM3812 models also do not have MIDI, which is essential if you have sausage fingers like I do, and need to use an external keyboard to control it. Though the PSS-480 does have a less-distinct sound than the YM3812 models, the nostalgia factor is not lost, and it will be a matter of moments before you’re figuring out how to play all the old video game themes from your past. Nostalgia aside, the 480 also has a quarter-inch audio output jack, so you can easily connect this keyboard to effects, which it takes to very well in my opinion. Spend some time getting to know the synth engine in this simple but fun instrument, and perhaps one day you will be ready to tackle the tedious but all-powerful DX-7.