MOTM

>
> Well, I hate to open this can of worms (mixer) again, BUT, it always
> generates some interesting and informative discussion.  Has anyone else
> checked out the Blacet site lately?  I thought his mixer was certainly
> thought provoking.  Seems that each input has gain both directions
> apparently with 180 degree phase reversal in one direction of the knob.
> So, looks like the mixer kind of doubles as a inverting attenuator / maybe
> with gain.


Corect, but being the clever folks we are would rather "build-in" this
feature
into each module. :)

>
> Anyway, I can see the advantage and handiness of having the inverter
> (separate).  However, I wonder how / why one might choose to invert the
> phase of one of the signals being input to a mixer.  The only thing that
> comes to mind is the cancellation that could be achieved between the
common
> parts of two signals.  Some of you guys enlighten me please.

99% it's for CVs, not audio. LFOs, for example. Inverted audio has no
meaning unless you
are trying to cancel out something (like a phaser! :)  )

>
> And what is the scoop with the "bias" control?  When I think of bias, I
> think of setting the mid point of the range where the signal rides on the
> input of an amplifier.  Back in my old tube days, the correct bias would
> assure that you were operating on the linear portion (or not, if that was
> your choice) of the tube's characteristic (input voltage to output
> current).  Seems like, on solid state, biasing off a center desirable
point
> would just result in ugly distortion.  What am I missing here?


It's a DC offset, again for CVs.

Paul S.

Well, I hate to open this can of worms (mixer) again, BUT, it always
generates some interesting and informative discussion.  Has anyone else
checked out the Blacet site lately?  I thought his mixer was certainly
thought provoking.  Seems that each input has gain both directions
apparently with 180 degree phase reversal in one direction of the knob. 
So, looks like the mixer kind of doubles as a inverting attenuator / maybe
with gain.

Anyway, I can see the advantage and handiness of having the inverter
(separate).  However, I wonder how / why one might choose to invert the
phase of one of the signals being input to a mixer.  The only thing that
comes to mind is the cancellation that could be achieved between the common
parts of two signals.  Some of you guys enlighten me please.

And what is the scoop with the "bias" control?  When I think of bias, I
think of setting the mid point of the range where the signal rides on the
input of an amplifier.  Back in my old tube days, the correct bias would
assure that you were operating on the linear portion (or not, if that was
your choice) of the tube's characteristic (input voltage to output
current).  Seems like, on solid state, biasing off a center desirable point
would just result in ugly distortion.  What am I missing here?

Well, I am not promoting the Blacet product here on the MOTM list, but
since many MOTM modules are centered around the "best" of some other good
designs, it seems appropriate to bring up what is at least a new feature on
a mixer to me.

Larry Hendry

In a message dated 11/28/99 12:29:45 PM, synth1@... writes:

>99% it's for CVs, not audio. LFOs, for example. Inverted audio has no
>meaning unless you
>are trying to cancel out something (like a phaser! :)  )

This is probably why many (most?) modulars have two distinct types of mixers 
-- plus the fact that some components are better suited for audio and some 
for DC. But this also brings up a question I've had about canceling out audio 
signals. I was thinking of adding some inverting attenuating inputs to some 
DIY VCFs I've got (since they only use half of a dual op amp for the basic 
inverting mixer they currently have -- a waste of 20 cents!). 

I thought this may in fact be useful (with one big caveat) for subtracting 
out harmonics in complex waves (like subtracting out a triangle from a 
sawtooth wave), BUT (the caveat) one would have to add the fundamental since 
that would be subtracted out entirely. I'm wondering if anyone has tried 
this, or sees it as being useful? I have tried some initial experiments with 
this, and have found that using (from one VCO) a SINE and inverted TRI (or 
SQUARE) and an in phase SQUARE (or SAW), sounds better to me than using the 
in phase TRI (or SQUARE). I really like the sound and wonder what others 
think.

JB

> From: "Paul Schreiber" <synth1@...>
> Corect, but being the clever folks we are would
> rather "build-in" this feature into each module. :)

Being the clever consumer I am (hey I subscriber to MOTM didn't I?), I
would rather see such features "built in."

> >  However, I wonder how / why one might choose to invert the
> > phase of one of the signals being input to a mixer.

> 99% it's for CVs, not audio. LFOs, for example. 

Of course.  I still have a hard time not thinking audio when I think mixer.
 Duh !!

> > And what is the scoop with the "bias" control?
> > What am I missing here?
> 
> It's a DC offset, again for CVs.

Sure !! (same stupid look on my face as before).

Thanks Paul.  All that should have been obvious to me, but I keep
forgetting to put my "modular" brain in gear.  Your explanations do help me
appreciate the Blacet design even more (well, from looking at the picture).
 Unfortunately, I guess I will be once again trying to drive up the
features / prices of the MOTM mixer when we get to that (or maybe that
accompanying reversing attenuator).

Larry (Stooge wanting something with an inverter) Hendry