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> I was under the impression that, despite the name, the Yamaha FM synths didn't actually use frequency Modulation but rather phase modulation. With Frequency m

> I was under the impression that, despite the name, the Yamaha FM synths didn't actually use frequency Modulation but rather phase modulation. With Frequency modulation you can't have an operator feed back on its self. It’s true that it’s phase modulation, but phase is just the derivative of frequency, and the derivative is a linear operator (essentially a 6dB/oct EQ). So I don’t think it’s an especially important piece of terminology to get correct. The statement about feedback is actually backwards. You cannot directly incorporate feedback into a phase modulation system. In the Yamaha system, the feedback is delayed by a sample to make it work. In an FM synth, this would not be necessary, and you could just directly feed the output back into the input.

weatherlight 5y ago
One thing that is different in the preenfm2 compared to the Yamahas stuff is, that it uses linear FM and therefore will not do operator feedback. The guy behind the preenfm2 says, that feedback is not that important, when you have a variety of waveforms for modulation. Linear FM also has the advantage of being a bit "friendlier/warmer" when using complex waveforms as modulators (Higher harmonics of the modulator will have a smaller effect than in phase modulation). One thing you loose when not having feedback: The normal feedback happens after the amplification/envelope if I remember correctly Therefore the amount of feedback scales with the amplitude. With feedback you therefore get less harmonics and therefore a "softer" sound at lower amplitudes. This is quite useful, because it mirrors the behavior of most natural sound sources. It is the same idea as using a lowpass gate or using the same envelope for the amp and the filter in subtractive synthesis. Of course FM synths give you enough options to get this effect in another way. I still like the yamaha style feedback though....
- klodolph 5y ago
  I will say—my personal experience, in dissecting DX7 presets, is that feedback is not really used that much. If you are porting DX7 sounds to a different architecture, you can remove the feedback and replace it with something like a noise source, or another operator, much of the time, or even remove it altogether. This is just my personal experience. I often dig through DX7 patches in order to reimplement them for demoscene projects. Sounds like you’re getting good use out of the TX81Z. I have the TX802, which is on paper a better synth, but controlling it from a DAW is much more of a pain because the program change messages control the “performance”, rather than the patch. So it’s been exiled from my rack, at least for now.
  - weatherlight 5y ago
    if you try to control the parameters on the TX81z while its receiving midi info, it starts to "skip" and the notes start to lag, lol. I wish i had a TX802 or a fs1r yamaha. Those are so nice!
  - ajxs 5y ago
    I have the same problem with the TX802. I do my best to avoid the 'performance mode' features entirely. Slightly related: I really love the build quality of Yamah's 80s/90s rack synths. The physical interfaces were very well-designed, and look amazing.
    - jacquesm 5y ago
      Agreed, and what's more: back then it wasn't all that apparent, the fact that they're still playing almost 40 years later is what proves it, most other gear - even very high end - from that era is long gone.
tgv 5y ago
I think direct feedback in PM is possible, at least for low modulation indices. The Yamaha implementation is in software, so a one sample delay is the easiest implementation (otherwise you'd have to solve a rather complex equation at every step).
- klodolph 5y ago
  The distinction that I’m making is exactly that. You can’t incorporate direct feedback into a phase modulation synthesizer, you need to incorporate delay into the feedback path. By comparison, you can use direct feedback with subtractive or FM synthesis. The one-sample delay basically turns the feedback into an iterated function system. With certain parameters, you end up with aperiodic results—cool in theory, but in practice, often just used as a noise source.
  - tgv 5y ago
    But if we take the simplest example, f(x) = sin(x + c*f(x)), we can solve it, (numerically). If I run it up to 0.5π for c=0.5, I get something that's (obviously) very close to the function with a short delay. So I take that as the possibility of direct feedback, although in a electronic circuit, feedback also has a minute delay.
    - klodolph 5y ago
      > we can solve it, (numerically) For certain values of x and c! You will end up with branch cuts for |c| > 1.
      - tgv 5y ago
        I think for all values of x, but c can’t be too large, sure. I had interpreted your statement as a complete impossibility. My mistake.
nyanpasu64 5y ago
> phase is just the derivative of frequency, and the derivative is a linear operator (essentially a 6dB/oct EQ). FM (if strong enough to create negative frequencies) and PM are equivalent when you're modulating a signal with a sine wave. As soon as you chain modulators, they're no longer mathematically equivalent or capable of producing the same sounds, since frequency-modulating a signal by a complex wave is different from phase-modulating a signal by the same complex wave (which can produce sharp corners given a bounded input with sharp corners).

weatherlight 5y ago

One thing that is different in the preenfm2 compared to the Yamahas stuff is, that it uses linear FM and therefore will not do operator feedback. The guy behind the preenfm2 says, that feedback is not that important, when you have a variety of waveforms for modulation. Linear FM also has the advantage of being a bit "friendlier/warmer" when using complex waveforms as modulators (Higher harmonics of the modulator will have a smaller effect than in phase modulation). One thing you loose when not having feedback: The normal feedback happens after the amplification/envelope if I remember correctly Therefore the amount of feedback scales with the amplitude. With feedback you therefore get less harmonics and therefore a "softer" sound at lower amplitudes. This is quite useful, because it mirrors the behavior of most natural sound sources. It is the same idea as using a lowpass gate or using the same envelope for the amp and the filter in subtractive synthesis. Of course FM synths give you enough options to get this effect in another way. I still like the yamaha style feedback though....

klodolph 5y ago
I will say—my personal experience, in dissecting DX7 presets, is that feedback is not really used that much. If you are porting DX7 sounds to a different architecture, you can remove the feedback and replace it with something like a noise source, or another operator, much of the time, or even remove it altogether. This is just my personal experience. I often dig through DX7 patches in order to reimplement them for demoscene projects. Sounds like you’re getting good use out of the TX81Z. I have the TX802, which is on paper a better synth, but controlling it from a DAW is much more of a pain because the program change messages control the “performance”, rather than the patch. So it’s been exiled from my rack, at least for now.
- weatherlight 5y ago
  if you try to control the parameters on the TX81z while its receiving midi info, it starts to "skip" and the notes start to lag, lol. I wish i had a TX802 or a fs1r yamaha. Those are so nice!
- ajxs 5y ago
  I have the same problem with the TX802. I do my best to avoid the 'performance mode' features entirely. Slightly related: I really love the build quality of Yamah's 80s/90s rack synths. The physical interfaces were very well-designed, and look amazing.
  - jacquesm 5y ago
    Agreed, and what's more: back then it wasn't all that apparent, the fact that they're still playing almost 40 years later is what proves it, most other gear - even very high end - from that era is long gone.

tgv 5y ago

I think direct feedback in PM is possible, at least for low modulation indices. The Yamaha implementation is in software, so a one sample delay is the easiest implementation (otherwise you'd have to solve a rather complex equation at every step).

klodolph 5y ago
The distinction that I’m making is exactly that. You can’t incorporate direct feedback into a phase modulation synthesizer, you need to incorporate delay into the feedback path. By comparison, you can use direct feedback with subtractive or FM synthesis. The one-sample delay basically turns the feedback into an iterated function system. With certain parameters, you end up with aperiodic results—cool in theory, but in practice, often just used as a noise source.
- tgv 5y ago
  But if we take the simplest example, f(x) = sin(x + c*f(x)), we can solve it, (numerically). If I run it up to 0.5π for c=0.5, I get something that's (obviously) very close to the function with a short delay. So I take that as the possibility of direct feedback, although in a electronic circuit, feedback also has a minute delay.
  - klodolph 5y ago
    > we can solve it, (numerically) For certain values of x and c! You will end up with branch cuts for |c| > 1.
    - tgv 5y ago
      I think for all values of x, but c can’t be too large, sure. I had interpreted your statement as a complete impossibility. My mistake.

nyanpasu64 5y ago

> phase is just the derivative of frequency, and the derivative is a linear operator (essentially a 6dB/oct EQ). FM (if strong enough to create negative frequencies) and PM are equivalent when you're modulating a signal with a sine wave. As soon as you chain modulators, they're no longer mathematically equivalent or capable of producing the same sounds, since frequency-modulating a signal by a complex wave is different from phase-modulating a signal by the same complex wave (which can produce sharp corners given a bounded input with sharp corners).