[sdiy] all analog FM synthesis?

[Magnus Danielson]

From: Johannes Öberg <johannes.oberg at gmail.com>
Subject: Re: [sdiy] all analog FM synthesis?
Date: Sun, 20 Feb 2005 03:02:48 +0100
Message-ID: <be546e56050219180239e2114f at mail.gmail.com>

Hej Johannes!

> You know all available "FM"-synths (like the DX-series) uses Phase
> Modulation and not Frequency Modulation, right? I know little about
> VCO construction, but Phase Modulation the way it's done in the DX
> synths (which is really a modulated sinetable scanning routine) must
> be terribly difficult to implement in analog technology!

No. Here is a conceptual idea of direct phasemodulation:
http://rubidium.dyndns.org/~magnus/synths/schematics/sawphaseshift.pdf
explanation is found on
http://rubidium.dyndns.org/~magnus/synths/schematics/

Another way to acheive something similar would be to diffrentiate the signal
before sending into the linear FM input. However, the linear FM input scales
with the CV sum, so the result of that would be scaled linear PM, which would
be fairly usefull too.

> They sound quite different; FM tends to sound like disharmonic and
> "bad" wierd FX sounds, while PM sounds like electric pianos and
> metal-hit-with-a-stick-harps.
> 
> A relative to PM, sound wise at least to my ears, is synced FM. Read
> all about it at www.clavia.se/nordmodular/Modularzone/Softsync.html
> (the latter half of the article). That should be easier to get to
> sound good from in the analog domain.

IMHO Softsync is something else. However, this form of sync is a bit different.
See the EM&M Spectrum article for a nice little discussion on the topic. Hmm...
time to re-read it.

> I don't have the skills to develop an analog FM synth, but I would be
> intressted in building one. I always loved the sound of FM!

Analog FM/PM isn't that hard to do really, it's just that it hasn't been
emphased. Add to that the different forms of hard/soft sync and then the CEM
wave-reversal sync.

Just a handfull of smaller additions is needed to acheive scaled PM and FM as
well unscaled PM and FM.

Maybe I should make the lab-exercise for you to listen to? Hacking a ASM-1 VCO
should be simple enought. It's a booring Sunday after all. ;O)

Cheers,
Magnus