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