Through-Zero FM

[Dan Slater]

    I think that you can get through zero FM with conventional FM oscillators by a
relatively simple patching trick.  Setup a standard FM patch with a fairly high
center frequency (5 KHz for example). Make sure that non of the sidebands are
folded over by having a too large modulation index. Then ring modulate this signal
with a 5 KHz carrier. You now get 2 sidebands, one centered at 10 KHz and the
other at 0 Hz. Use a low pass filter to separate the lower sideband only. The
lower sideband has the through zero FM output. You can vary either the FM center
frequency or ring modulator carrier to shift the through zero FM signal center
frequency away from zero Hertz.

    I believe that that this approach provides results identical to a through zero
FM oscillator. The advantage is that you can do this on almost any modular
synthesizer. Some analog frequency shifters such as the Bode / Moog include a
through zero frequency shift capability. The through zero shift is either obtained
by a quadrature oscillator with a through zero shift (Serge) or by a through zero
hetrodyning approach (Bode). The patch outlined in the first paragraph is this
latter method.

Dan Slater



WeAreAs1 at aol.com wrote:

> Hello DIY listmates,
>
> I have read the term "through-zero FM" several times, in previous posts found
> here.  Usually with the writer referring to it in glowing terms lavish with
> praise.  I, too, now wish to wallow 'n' revel in the wholesome goodness of
> through-zero FM.   So, could someone please be so kind to explain the concept
> to me?  (and to the rest of the list, of course!)  Also, what are some musical
> applications and sonic characteristics of through-zero FM?
>
> Very best regards,
> Michael Bacich