Archive of the former Yahoo!Groups mailing list: MOTM

OK, here it is by popular demand. :-) The review isn't
exactly "mini" as Mike Marsh reported. I'm too long winded for that!
∗∗∗∗∗∗

Don't tell anybody, but my Synthesizers.com system actually has
a "special guest slot" for MOTM and Blacet modules, which use the
same power supply as dotcom and are deemed worthy of my beautiful
Beast of Euless. The latest guest (resident, actually) is the long,
Long, LONG awaited Encore Frequency Shifter. In this regard, the
module shares more than just its format with MOTM (this digression
brought to you by Satan). Then again, some things are worth waiting
for and this module seems to have been one of them.

I've been waiting for this product to hit the market because it seems
to be the first design that isn't just a rehash of the famed Bode FS
in one way or the other. In a frequency shifter design, everything
has to be perfectly balanced or it all goes to hell, so it's no
wonder that some designs have as many as 40 trim pots. That, of
course, means 40 things that can go out of adjustment. An important
part of any frequency shifter design is the quadrature oscillator,
which generates two sine waves 90 degrees out of phase with each
other. For best results, this relationship must be kept constant.
Encore ensures this by using a RISC processor to generate two sine
waves that are always perfectly 90 degrees apart and just the right
amplitude (I'm not sure why it took something as powerful as a RISC
processor to do the job, but I'm not about to bitch about something
that works so well). These waves are multiplied with the input signal
to shift it up or down by the same number of Hertz. As a result, this
extremely clever design only seems to use fewer parts and generates
spectra that can only be described as pristine. This is welcome,
because if things are unbalanced you will get the carrier (quadrature
oscillator) bleeding into the output, which ruins the effect. To get
around this, some of the better frequency shifter designs employ a
squelch circuit that hushes the output when there is no input so that
you won't detect the carrier frequency and your ear-brain won't hear
it in the output signal (think of how a ring modulator is ∗supposed∗
to suppress the X and Y inputs, but few of them do a very good job of
it). With the Encore design, rabbit tricks like this aren't really
necessary.

What does Frequency shifting sound like? It is akin to ring
modulation, except with more elegant and satisfying results. A
frequency shifter transposes the frequency components of a signal by
the same number of Hertz, so the harmonic relationships aren't
preserved (unlike with pitch shifting). The result is an
enharmonic "clang tone" or bell-like sonority, in most cases. This
can either sound trashy or sophisticated, depending on how you use it.

So what are the features of this module? Jacks are audio input, CV
in, Up shift out and down shift out. As an added bonus, you also get
access to the quadrature oscillator, which offers sine out and cosine
out (they both sound like a sine, but are shifted 90 degrees out of
phase). Controls include initial shift (rough shift) fine shift,
input gain, sine and cosine output attenuators, up and downshift
feedback controls, and a CV input attenuator. You can guess what the
attenuators do, so I'll skip those. What's interesting is that this
is a "through zero" design, meaning that you can apply the frequency
shifting effect down to subaudio. Why would you want to do this?
Because at those settings the output sounds much like a phasing
effect. To make things more interesting, you can apply the Up and
Down feedback controls to get deep phasing effects and other exotic
sonorities. What, not enough? Take the Sine and Cosine Outputs and
use them to modulate separate filters. Now you are into Tomita
Territory, domo arigato! Other amazing effects are left as an
exercize to the reader.

Now for the interesting stuff:

THE BAD PART:

This design has ample space on the front panel for another jack and
control, so why Encore chose not to add a combined up/downshift
output and mix control like the Doepfer has, I don't know. It would
have been easy to do and quite convenient.

It's great to have the sine and cosine waves available as a bonus
feature and they are quite useful. But because they are digitally
derived, they have a definite "stepped" quality at low frequencies,
which can be annoying in some situations. Slew limiters will fix
this "problem" easily enough, but it's still kind of annoying.

The very high impedance CV input doubtless provides important circuit
protection, but it makes the voltage control a bit fishy in some
instances. For example, you can sweep the shift frequency through its
full range just by inserting a patch cord and touching the tip of the
opposite plug! The range is another thing that is a tad
disappointing. The control voltage is 0 to 5 volts. Anything below or
above that range has no effect. And a full five volts only causes
about a 500 Hz shift! That small range makes the input attenuator
almost superfluous. Indeed, the CV input should more accurately be
called a "modulation input." The doepfer FS offers a much wider and
more useful range of sweep. While I'm at it, a 1V/Oct CV in would
have been really nice, as it would allow you to play tuned noise, etc.

Apparently, any DC offset on the input will cause the carrier to
decay after input is removed rather than simply not sounding. This
can be mildly annoying if you are using the FS as the last stage in
your audio chain. Otherwise you could just gate the offending
frequency out using an envelope follower and a VCA to form a squelch
circuit. An even easier solution would be to AC couple the input
using a capacitor (as found on the dotcom Connector Interface
module). Mind you, my description of this anomaly sounds worse than
the actuality.

I could also swear that the Doepfer FS sounds a bit richer than this
design. Indeed, I remember synthesizing some very realistic gongs
using the Doepfer, which I've yet been able to do with this Encore--
but give me time.

THE GOOD PART:

This module rocks!

Although the design will be a merry blue bitch to reformat for
dotcom, MOTM users will be delighted with the layout. It lacks the
physical "heft" of MOTM modules, but you are going to mount it, not
fondle it, if you will pardon the sexual allusion. The circuit
quality is certainly worthy of MOTM and other fine systems. It's
QUIET. Best of all, it works wonderfully well. The thing I didn't
like about the Doepfer design was that it had quite a bit of carrier
bleedthrough which really detracts from the frequency shifting
effect. This design significantly suppresses that local oscillator
tone, so you get an output that is far more refined. Indeed, this
design has a wonderful clarity of tone to it that is really quite
appealing.

The stellar specs of the Encore frequency shifter are enough to
recommend it (especially at $389!) but the quadrature outputs,
feedback controls and through-zero shifting are enough to make you
want to offer your firstborn to it. Who could blame Robert Rich for
having a glorp orgy with his Encore demos? This design invites--nay,
DARES you to patch it in exotic ways for hours on end. If this isn't
one of the most versatile frequency shifters on the market, I'll
cluck like a chicken and eat Fruity Pebbles(TM).

Despite a few minor drawbacks, the Encore Frequency Shifter is a
refreshingly new design that harnesses a microprocessor to do away
with legions of trim pots and the problems thereto while offering
superior stability, SNR and carrier rejection. It's a very high
quality design that I predict could eventually outsell all others and
was well worth the wait. You won't have to wait to get it, though--
Encore is extremely prompt with shipping and responsive to inquires.
Talk about a winning combo!

johnm