[sdiy] all analog FM synthesis?

[Mattias Rickardsson]

At 02:19 2005-02-21, Johannes Öberg wrote:

>(I'm replying to many authors at once; should I stop this?

I actually prefer that, so I don't complain. :-)

> >But they are essentially almost the same:
> >So phase modulation should sound like FM with a constant-slope HPF:ed
> >modulator (i.e., derivative of the modulator), which means there is much
> >more treble content in the modulator.
> >To some extent, I think it should be possible to use a constant-slope LPF
> >on the phase modulator in order to make it sound like FM (and vice versa).
>
>Is this based on theory or experience? I can see why it *should* work,
>but hardly why it would :-)

It probably should work, :-)  at least considering the frequencies, but 
what I haven't taken into accont is the recently mentioned group delay and 
similar time-related things. Maybe it's "impossible" to make a filter that 
has all the right characteristics. But anyway, I think it's good to know 
the parallel anyway.

>I know next to nothing about the math behind FM and PM, but I've been
>playing around with both of them on my synthesizers, and in my
>experience they sound very different, to the point where synced-FM
>sounds more like PM.

[if you refer to analogue synths,] That's probably because the non-synced 
FM isn't exact enough, and the phases of the expectedly equally-tuned 
oscillators drift apart. Synced FM, on the other hand, keeps the 
oscillators cycles starting at the same point in time. Like in PM, where 
the oscillators always stay in phase.
That's what I meant when saying that analogue PM is easier to do correctly 
than analogue FM.

>Where PM wants to sound like an electric piano,
>FM always tend to sound like your using a circle saw on an electric
>piano... (which might not be a bad thing depending on taste)

I actually love demolished guitars much more than d:o pianos... ;-)

> >Maybe I should make the lab-exercise for you to listen to?
>
>Väldigt gärna!

Åström-Hägglund! ;-)


/mr  -  exploiting all our 29 letters