As I worked on this, I was once again reminded of the vast difference between the DX7 and Thor. The Harmonica 1 sound, at least the way I envisioned it, is a bit richer than most patches I've written so far. And yet for it's complexity, it's really a simple patch.
We'll start with that. FM8 shows it as a 4-op patch. So judging between the visual data behind Harmonica and the actual sound, we see it's a DECEPTIVELY simple patch. No, there won't be any need for using a resonant filter as a 4th oscillator. But we do need all our modulation resources. I'm not necessarily going to attempt a direct emulation of the Harmonica structure. Rather, this time, I'm going for a somewhat imitative timbrel quality which will be modulated by three EGs and an LFO.
Let's start by getting the basic timbre down. We have a chain of 4 ops. We'll get a better approximation if we use Osc1 in place of A and B, Osc2 in place of C, and Osc3 for the carrier. Initially, we'll ignore using any FM amount in osc2 and 3. A and B have the ratio 7.62:5.056. What do we know about decimal values in Thor? Thor doesn't like them. So let's think about them in terms of notes in the C scale. 7=Bb, 5=E. 7.62 is equivalent or approximate to the leading-tone 7th, B natural. So we'll set the ratio for the nearest harmonic interval of a 5th--5:4, or G:C. To make this work for us, we set the semi to 4, raising them both a major 3rd to get closer to the ratio we need.
The next part arises from an ongoing complaint I have about Thor's implementation of FM. This specifically has to do with how Thor handles oscillators modulating each other and all the pitch instability it causes, radically shifting the pitch in most cases. This is obviously avoided by using Key Note to scale the effect. The inherent problem with this approach, however, is that the effect cuts out at C3 with scaling at 100. I'm not going to take the time to further fix the problem now for this patch, but I think what happens next is interesting.
Route Osc1, amount 100, to Osc2 FM. You'll need two scales. Set the first amount to 63, Filter Env, and the second to 60, Mod Env. Route Osc2, amount 68, to Osc3 FM, and scale first amount 40, Amp Env, and second amount 90, Key Note. What this does is link up all 3 oscillators without making them TOO perfect. I didn't use keyboard scaling with the first set because I thought a little instability and noise in that part of the chain wouldn't be such a bad thing, and I wanted to use the mod and filter envelopes to try to recreate a kind of breakpoint effect that the DX7 uses and is absent in Thor.
We don't need filters for this one. We do need a little vibrato, however, and this is where the designer's ear comes into play. The original DX7 patch has a dramatic vibrato whose rate is keyboard scaled (the higher you play, the faster the vibrato). I don't really like doing things that way, so I'm going to keep the vibrato constant. Set LFO1, amount 13, to Osc3 Pitch. Set LFO1 rate to 5.26Hz, triangle wave. Mod Env A 9.0 ms, D 3.2 ms, and R 3.2 ms. Filter Env A 78.8 ms, D 423 ms, S -3.7dB, R 7.50 s. Amp Env A 34.9 ms, D 4.73 s, S -13.4 dB, and R 423 ms.
To finish up, notice that FM8 oscillators are not perfectly tuned to harmonic ratios. The differences are mostly very slight and subtle. You can detune the oscillators to reflect that. For my taste, however, the timbrel variation strays to far from the sound I'm trying to get, so I just substitute the chorus effect. It should be very subtle, and I'll leave the reader his/her own judgment as to what it needs.
And that's it for a simple FM harmonica!
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