To describe a sine wave mathematically we write the voltage function of time
as
V(t) = sin(ct)

where c is a constant. We can show that c is in fact the frequency, or
cycles per unit time (if we normalize to radians). c may be taken to be
negative, but in all cases we have the identity:

sin(-ct) = -sin(ct)

Therefore "negative frequencies" can be achieved by setting the oscillator
to the corresponding positive frequency of equal magnitude and running it
through a voltage inverter. Now, turning the frequency dial through zero
from c to -c is a much different transform than feeding a frequency +c
signal through a polarizer and turning the polarizer from +1 to -1. But the
start and end points are the same.

-Monroe

On Fri, May 23, 2008 at 2:27 AM, omegaattraktor < omegaattraktor@... >
wrote:

> --- In Doepfer_a100@yahoogroups.com <Doepfer_a100%40yahoogroups.com>,
> "Monroe Eskew" <monroe.eskew@...>
> wrote:
>
> >
> > That sounds like thru-zero amplitude modulation, which is nothing new,
> > though it is a nice feature to put within one module. But thru-zero
> > frequency modulation Still confused.
>
> negative frequencies has nothing to do with inverted phase. it means
> that the signal is going its way back. but of course the time continuum
> will not be affected. this can happen at any amplitude of the signal,
> therefore it doesn't invert the phase.
>
> negative frequencies do occur with large amount of fm. imaginge the
> frequency of an osc with 1kHz is modulated by another osc. if the
> amount of modulation is increased there is a point when the frequency
> is modulated between 0kHz and 2 khZ. if you increase the modulation
> further the frequency finally goes to negative. thru-zero fm just means
> that an osc can handle this.
>
> regards,
> oliver
>
> http://www.namshub.ch/
>
>
>

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