MOTM

So, here are my very subjective assessments of the MOTM 320 VCF compared to
the R.A. Moog 904A VCF.  Again, these are very different beasts.  The Moog
is a 24db/oct filter while the MOTM is a 12db/oct filter.  The Moog filter
does not overload as easily as the MOTM and does not have a built-in
reversable attenuator (although one is available on the standard Filter
control panel).

I was quite suprised at how similar I could get these two filters to sound
with low level inputs.  I just used the sawtooth output of the MOTM 300 as
input to both filters.  With no resonance on either filter, the difference
between the slopes was evident though.  I could hear more harmonics coming
through on the MOTM.  

Both filters seemed to have non-linearities as the resonance was cranked.
I can't quite describe the character of each in words but both were very
cool sounding.  

I guess the best description of the difference between the two is that the
Moog filter is naturally darker because of the sharper slope.  As the input
level increased, both overloaded in neat ways.  I think the Moog was a bit
more "throaty" at higher resonances with a bit more of a vocal formant
sound while the MOTM was more "fuzzy" at similar resonance levels (great
subjective terms, eh?).  Maybe another way of describing the difference was
that the MOTM sounded more "muscular" than the Moog when overloaded.
Again, both were very musically useful and interesting.

I tried using a sample & hold with a slow sawtooth input on both filters to
get them jumping around the frequencies to hear differences.  I was again
surprised at the similar sound I could get out of the MOTM at low input
levels.  The Moog sounded a tad bit better in this situation wtih the
resonance cranked getting just a bit more of the classic strong "beeoow"
sweep sound.

I think both filters can be quite agressive sounding with overloaded inputs
with the MOTM having a generally stronger agressive sound (aka MS-20 like)
while the Moog has more of a classic sound.

I don't know if this helps anyone out there but I couldn't think of any way
to compare these two filters scientifically or even objectively!  If anyone
has some ideas, I'd be happy to try them.  I've certainly learned a lot
doing these comparisons.

BTW, I found out what was happening with my sawtooth tests when mixing the
MOTM and Moog saw waves together.  The MOTM 300 has a downward sawtooth
wave while the Moog has an rising sawtooth wave.  When mixed together, they
produce something like a pulse wave and as their phases/pitches change, a
form of PWM occurs.  I watched this on an ancient Heathkit scope, it was
quite interesting!  I changed the phase of the MOTM oscillator (Moog mixer
panels have both + and - outputs; hint, hint Paul) and lo, the summed wave
looked more sawtooth shaped.  I like the Saw-Width-Modulation that came out
of this and will use it in the future!  It is different than the
traditional PWM sound.

	Eric

> I was quite suprised at how similar I could get these two filters to sound
> with low level inputs.

This is important to note! The '420 is designed *on purpose* to overload the
filter,
because that's what the MS-20 did (does).

> I just used the sawtooth output of the MOTM 300 as
> input to both filters.  With no resonance on either filter, the difference
> between the slopes was evident though.  I could hear more harmonics coming
> through on the MOTM.

Correct.

Now put *two* '420s in series, both on LP!

>
> Both filters seemed to have non-linearities as the resonance was cranked.
> I can't quite describe the character of each in words but both were very
> cool sounding.

The '420's Q is a function of the input level. High high input levels, the Q
is shifting
as the input waveform. Freaky!

>
> Maybe another way of describing the difference was
> that the MOTM sounded more "muscular" than the Moog when overloaded.
> Again, both were very musically useful and interesting.


Nice to hear that the humble '420 is holding it's own against Dr. Bob.

>
> I tried using a sample & hold with a slow sawtooth input on both filters
to
> get them jumping around the frequencies to hear differences.  I was again
> surprised at the similar sound I could get out of the MOTM at low input
> levels.  The Moog sounded a tad bit better in this situation wtih the
> resonance cranked getting just a bit more of the classic strong "beeoow"
> sweep sound.

The upcoming '440 will 'beeoooww' as well.

Paul S.