Frequency Shifter Comparison (LONG)
2006-01-31 by Chris Sawyer
FWIW, John, here is my comparison of the Serge
and Modcan frequency shifters. Sorry for the delay in posting about this, but I
have been battling illness for almost a week. (Looks like I'm finally kicking
it.) Hopefully the wait will be worth it for those interested.
The most significant difference between the Serge
and Modcan FS is that the Modcan offers "through zero" shift and a linear mode,
whereas the Serge is unidirectional with exponential shift only. The
Modcan's linear mode allows you to dial in certain shifts that would be
difficult to tune in exponential mode, and the modulation effects can
be much different. My sound clips include an example of the
Modcan's linear shift with bidirectional modulation.
The sound of the two in exponential mode is
very similar, as you will hear in the demos below. One interesting nuance: when
the Modcan is in exponential mode with the manual shift knob set to zero shift,
neither the CV input nor the 1v/oct input
will modulate its shift i.e changing from -0- shift to >0 shift;
only after you introduce some manual shift will voltages begin to impact
the signal, as though the built-in quadrature oscillator is completely off at
zero and cannot be "disturbed" (to use Wiard vocabulary) into action using
external CV. In contrast, the Serge will allow you to set a base shift of -0-
and introduce shift using an external voltage--this can be very useful
in certain patches. I also prefer the Serge's bipolar CV attenuator to the
Modcan's unipolar control. I seem to get more "creative" results using the Serge, but this may be
due to its proximity to other great audio and CV modules (score one for
Rex's "systems" philosophy).
The Modcan's large manual shift knob makes it very
easy to dial in precise amounts of shift, and because of its through-zero
design, if you decide you would rather use down shift than up shift,
you don't have to change the patch cable--you can simply turn the knob to
the opposite side of zero and the up shift jack outputs down shift signal.
The Modcan's jacks are labeled "sum out" (up shift)
and "difference out" (down shift) and this hints at an alternative use
of the frequency shifter: combining the sum/up and difference/down outputs
produces the classic ring mod sound. In the past I have performed an A/B
test of this technique using the Serge Ring Mod and FS modules, with
identical results provided that the Ring Mod's "carrier in" knob was set
below the waveshaping threshold.
Although both units contain a level control,
the Serge includes a CV jack for this VCA, giving it additional AM
capabilities. You can even route the internal sine VCO outputs to the VCA, as I
did in one of the samples below. While both
units also permit you to tap the quadrature sine waves for use as control or
audio sources, I found that the Modcan oscillator would tune to much lower
LFO rates.
Now to the audio clips. Most of the FS demo clips I
have heard are focused on freq shifting external sound sources such as vocals
and drums, so I decided to demonstrate the effects of the FS on
internal synth sources, using a Serge NTO as the signal that was
shifted by the Serge and Modcan FS. In many of these samples I patched the
Serge and Modcan outputs to the two inputs of a Serge cross-fader so I
could contrast the two FS in the same clip.
1) Serge
Exp Sweep: up shift output exponential sweep through range. Note there is no
down shift because it is not through-zero.
2)
Modcan
Exp Shift: sum output only (up shift) exponential sweep through range. You first
hear the up shift and then the down shift as I sweep the knob above and then
below zero.
3)
Modcan Linear Shift: sum output only linear sweep through range. Again you
hear both the up and down shift from the same output.
4) Modcan Thru0 Quad Mod: sum output set at -0- shift modulated by a Serge QUO quadrature oscillator you hear the through-zero shift as the quad osc alternately pushes the shift to either side of zero.
5) Sequenced Freq Shifts: 8-step sequence routed to the CV input of the freq shifter sequenced Serge FS is followed by an LFO mod during the cross-fade to the sequenced Modcan FS.
6)
FS
Ring Mod Compare: you hear three ring mod sweeps Serge first, followed by the
cross-fade, then the Modcan alone.
7)
FS
Sine Osc Compare: audio sines into cross-fader and two CV sources (LFO and
sequencer) into an Active Processor you hear progression from Serge raw
wave to Modcan raw wave to Modcan LFO mod to Serge LFO mod to Serge
sequencer mod to Modcan sequencer mod.
8)
FS LFO Rate Compare: NTO run into Serge Variable Slope filter, with
frequency modified by the output of an Active Processor, which selects between
the 90°
outputs of the Modcan and Serge FS. The first mod source you hear is
the Modcan tuned as low as I could get it; the second is the Serge with its
frequency and fine tune pots at their lowest settings AND an external CV of
-5 volts from a Scaling Buffer; the third is the Serge minimum manual tuning
with the cord from the external CV removed.
9)
Serge
NTO Freq Shift: non-shifted sawtooth gradually cross-faded to blend and then
shifted saw, shifted waveshape changed to square and cross-faded back to
blend and then to non-shifted square.
10)
Serge
FS Use of VCA: the VCA level is set to about
2
oclock; initially no
sound gets through, first hit with Cyndustries ADSR then mod source is switched
to Serge quad osc with frequency increased to low audio range for
AM.
11)
Serge
FS Pseudo PWM: NTO Variable out set to PW run into one side of cross-fader. Same
out routed to up shift and run to other side of cross-fader, with the
FS
90°
out controlling FS internal VCA. First you hear raw NTO wave followed by
blended version, with solo FS heard
last.
I
hope these prove useful to someone! Note that my e-mail is cross-posted to
the Modcan list but the sound clips were uploaded to the SMOG files
section since the question originated on the Serge
list.
Chris