Igor,
Think about it.... One ring modulator yields sum and difference
frequencies mixed together. The expense in the FS AFAIK is in a
filtering network that splits the sum out to one output and the
difference to another. There are several compromises to be addressed in
this filtering network. Difficult design, a lot of parts and labor to
get it all tuned right.
That's why it's so expensive.
The Doepfer FS I believe has a fairly basic version of this network...
it can do some frequency shifting but it is compromised in terms of
performance... I am not speaking from direct experience but according
to the doepfer web site that shifts of < ~ 50 hz are not possible. I
guess that handling the smaller shifts involves more difficult design
and construction. Also in the Doepfer, I think I heard that signal
bleed-thru is a problem (incomplete suppression of signal or carrier).
So perhaps the application of the Doepfer FS is more limited to doing
klangy distortion and robot voices than more subtle effects, but hey,
they offer it at a fraction of the price of anyone else.
Other things to consider:
The Wilson Analog Delay (WAD) Serge module does pitch shifting, but the
pitch shift can't be constant... so you can do vibrato and doppler-type
shifts with it, as long as the "dv/dt" is not zero (sorry, my calculus
is showing). Blacet makes a similar module (VC analog delay), I think
Big Briar too. You can do this with some digital delays as well, since
in each instance you're changing frequency output by varying a master
clock rate.
ANOTHER module that can do pitch shifting is a notch filter or phase
shifter. The shift amounts will be very small but if you shift the
phase you're pushing the wavefront forward or back... again, it has to
be changing to work (remember dv/dt <> 0). So you can do vibrato and
some FM types of effects with a phase shifter.
Guys if I don't have this right let me know.
JP
dahlia13@... wrote:
Think about it.... One ring modulator yields sum and difference
frequencies mixed together. The expense in the FS AFAIK is in a
filtering network that splits the sum out to one output and the
difference to another. There are several compromises to be addressed in
this filtering network. Difficult design, a lot of parts and labor to
get it all tuned right.
That's why it's so expensive.
The Doepfer FS I believe has a fairly basic version of this network...
it can do some frequency shifting but it is compromised in terms of
performance... I am not speaking from direct experience but according
to the doepfer web site that shifts of < ~ 50 hz are not possible. I
guess that handling the smaller shifts involves more difficult design
and construction. Also in the Doepfer, I think I heard that signal
bleed-thru is a problem (incomplete suppression of signal or carrier).
So perhaps the application of the Doepfer FS is more limited to doing
klangy distortion and robot voices than more subtle effects, but hey,
they offer it at a fraction of the price of anyone else.
Other things to consider:
The Wilson Analog Delay (WAD) Serge module does pitch shifting, but the
pitch shift can't be constant... so you can do vibrato and doppler-type
shifts with it, as long as the "dv/dt" is not zero (sorry, my calculus
is showing). Blacet makes a similar module (VC analog delay), I think
Big Briar too. You can do this with some digital delays as well, since
in each instance you're changing frequency output by varying a master
clock rate.
ANOTHER module that can do pitch shifting is a notch filter or phase
shifter. The shift amounts will be very small but if you shift the
phase you're pushing the wavefront forward or back... again, it has to
be changing to work (remember dv/dt <> 0). So you can do vibrato and
some FM types of effects with a phase shifter.
Guys if I don't have this right let me know.
JP
dahlia13@... wrote:
> Thanks! That's as lucid and down-to-earth an explanation as I
> could've asked for. So basically, a frequency shifter allows you to
> send the sum and the difference frequencies to seperate outputs (that
> must sound interesting with one output panned hard left, the other
> hard right), whereas a "conventional" ring modulator doesn't allow
> you to seperate the two. That's the main difference?
>
> What I was referring to as an octave divider sounds like what's being
> called a pitch shifter in this thread. For some reason, I always
> thought a pitch shifter was strictly a digital device that changed
> the pitch of sampled audio input without altering the length/speed.
>
> 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?
>
> Igor.
>
>
> --- 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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>
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