MOTM

At 5:02 PM -0500 1/24/03, The Old Crow wrote:
>
>   I am back from NAMM, and can elaborate.  The CS-80 filter EG and the
>MOTM-880 are a bit different, so I will describe both:

Thank you, I appreciate your taking the time to explain all this.

>   Attack Time (AT)
>   Decay Time (DT)

Based on your descriptions, regardless of what Yamaha might have
called these, more accurate names for these functions would have been
Attack Rate and Decay Rate.

(As you know, this is the case with almost all analogue ADSR's -- the
knobs control current sources charging a cap, so their settings only
translate to time values if the attack level and sustain level are
fixed, and unlike the CS-80 the sustain usually isn't fixed.)

>MOTM-880:
>
>   Initial Level and Attack Level have the same action as in the CS filter
>EG, and the same ranges.

Excellent :)  I've already explained in my last two posts to this
thread why I think Attack Level is such an important feature.

If the CS-80 EG is analogue, wouldn't there would be a bit of a slope
as it drops from the sustain level to the initial level??  I also
wonder if Roland were looking at the CS-80 when they designed the VCF
EG for the TB-303.

>Each also can be set by a 0 to +V CV.

Do the CV inputs completely replace the knob settings, or do the CV
inputs modulate the knob settings??

>   Attack, Decay and Release Times are 3ms to 30 seconds and are also
>adjustable with 0 to +V CVs.

Are these settings actual rates, or are they really times??  Imho,
this is a very important distinction.  If Decay is a rate, then you
get this nice "natural" effect of higher attack levels resulting in
longer decays.

While 30s is certainly long enough, I don't know if 3ms is punchy
enough for driving a VCA.  Or is this being designed primarily as a
filter envelope??

>   Sustain Level:  The MOTM-880 has ajustable sustain from -5 to +5, also
>adjustable with a 0 to +V CV.

I'm thinking that would give this module a bonus feature -- it can be
used as a voltage buffer, just like the 800 can be used as a voltage
source.

>   There is a 3-position switch to select the point at which a TRIG OUT
>pulse is generated: when the attack peak is reached, when GATE IN goes
>inactive or when the end of the cycle is reached.

Wow!! That gives it a whole mess of new functions!!

However, I do notice that it does not have a trigger input.  If it
did, it could be used as a trigger delay, a VC LFO, and not the least
expected feature, an envelope generator when using a trigger!!

So how does it respond to gates that drop before the attack or decay
phase is over??  I guess that's the question.

As you know, the 800 has three different modes, including a
trigger-only mode that it produces Attack-Decay envelopes using the
Attack and Release knobs.  The UEG has several options how it handles
dropped gates, including a one-shot mode.  Whether this is
implemented using two switched jacks, or one jack and a toggle
switch, the ability to respond to a trigger is essential for a
full-featured EG.

Imho, I would replace the manual gate pushbutton or the inverted
output with a switch or trigger input jack.

>   Normal and inverted envelope outputs.

Many of the inputs within the MOTM system have reversing attenuators, and
I haven't found the "negative" outputs of the 800 all that useful.
An output inverted in the intuitive sense (upside down), where 0V is
5V, and 5V is 0V, would have been much more of a feature.  Perhaps
there is no complimentary function for a bipolar envelope, although I
am thinking that maybe I should look into modifying my 800's.


>  > As much as I appreciate all of the ideas expressed in this thread, it
>  > supports a massive amount of features.  Imho, too many to fit into
>  > one module.   So I suggest the best approach would be a division of
>  > labor over several different modules.
>
>   Oddly enough, the 880 is a 2U module.  My prototype undimensioned
>placement guide shows the layout:
>
>http://www.cs80.com/motm880/motm880.gif
>

Yes, while it is not possible to include every possible feature in
2U, the features you chose to include are very clever.

Several people said they want knobs for each CV function, which would
have added six knobs to the MOTM-880 making it 4U.  Imho, such knobs
are not necessary, and afaik, the Serge and Blacet VC ADSR's don't
have that feature either.

Anyway, perhaps more elegant way to label the CV input jacks for the
traditional functions, might simply be "A" "D" "S" "R".

>   I am building three prototypes,

That's good, I only need two ;)

>and things like the LED colors are under
>PIC control, so if they need tweaked later, it is no problem.

Is it all digital??