SergeModular

Although an analog frequency shifter has (at least)
two ring modulators inside, there is a lot more
circuitry as well. There is a phase delay network
(PDN) which generates two versions of the input signal
with a 90 degree phase difference between them. There
is also a quadrature oscillator which generates sine
and cosine waves at variable frequencies. Then there
are summing amps, an input and output section, etc.

All these circuits must be fairly precise as well,
because any undesired nonlinearities or harmonics will
show up as artifacts in the shifted outputs.

I believe the external carrier version of the Serge FS
is more expensive because a second PDN is needed in
order to generate a quadrature signal from the single
carrier input signal.

-Chris M.

> This may be a naive question, but if a frequency
> shifter is basically
> two ring modulators in parallel, why are FS's so
> expensive? For the
> price of one Serge FS (external carrier), a person
> could buy 4 or 5
> of the ring modulator modules...does anyone have any
> theories as to
> why this is? Is seperating the sum/difference
> frequencies more
> difficult to achieve than producing both of them
> combined?

>
> --- In SergeModular@y..., John Papiewski
> <johnp@w...> wrote:
> > Hey Igor,
> >
> > You can think of a frequency shifter as a ring
> modulator with TWO
> > outputs: the upshift output has only the sum of
> the two input
> > frequencies, the downshift output has only the
> difference
> frequencies.
> > Serge has two FS's in their catalog, the internal
> carrier model,
> which
> > has an onboard sinewave oscillator, and the
> external carrier, which
> lets
> > you use your own sinewave or some other waveform
> or complex source.
> >
> > Please note that since it is ring modulator based,
> a frequency
> shifter
> > is NOT a pitch shifter! A frequency shifter will
> add the carrier
> > frequency to all the harmonics of the sound you
> want to shift. The
> > greater the carrier frequency, the more pronounced
> the harmonic
> > distortion. This is suitable for, well,
> distortion effects like
> > robot/computer/alien voices, etc. At very low
> carrier frequencies
> the
> > FS will simply impart vibrato, mild doppler
> effects, leslie effects
> etc
> > since the harmonic distortion is more subtle and
> harder to notice.
> >
> > A pitch shifter on the other hand will multiply by
> the harmonic
> > frequencies, keeping the original sound's harmonic
> structure
> intact, so
> > you can *transpose* the original sound by an
> octave, fifth, or some
> > other arbitrary interval. You can't do this with
> a frequency
> shifter as
> > far as I know.
> >
> > Make sense??
> >
> > John P.
>
>
>
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