MOTM

At one time I intended to be a purist and not buy any module containing
a microprocessor. Part of my reticence was due to the lack of kits in
this genre. That didn't last long. First I bought an Encore Frequency
Shifter. Then of course a MOTM-650. Added to my collection now are the
Encore UEG, Modcan Dual Quantizer, Modcan CV Recorder, and, soon, the
Modcan VCDO. Of course I want a Cloud Generator too! I probably
represent a small customer niche, but what I like about such modules is
that they sport analog-like user interfaces (the MOTM-650 not
withstanding its menu system). I like being able to set up modules
using knobs and buttons. I do not wish to hook up a computer to my MOTM
to control it. (I did try it to get a MIDI soft sequencer going - oh
the pain - the pain of trying to control my MOTM with a mouse.) If you
wander on over to the Modcan website and check out the latest Modcan B
module, you can see the analog interface trend being continued there.
The Quad Envelope Generator 60B contains 4 digital envelope generators,
each with 6 parameters. It's is programmed with 6 knobs and 3 buttons,
with a few LEDs to keep track of where you are. I like that sort of
interface! It is clean and simple, and powerful. Settings are saved
between power cycles. So you have a small programmable module without
any screen, even an LCD. I'm impressed. I like this trend, and I hope
Paul takes note. I'm not opposed to an LCD if there is room. I don't
mind embedded microprocessors. But you can see why I lurked silently
over the thread about how to extend the Cloud Generator be controlled by
USB, MIDI, Ethernet, Bluetooth and iPhone. Give me some knobs and
switches. I'm old fashioned. I love to kick back and play without
having to boot up a computer.

If this seemed like a rant, it wasn't. There are many ways to control a
synthesizer and using a computer is a valid one. I'm just offering a
point of view.

Richard Brewster
http://www.pugix.com

Well said/typed. You're not alone; I agree with you 100% on this
topic. This trend also extends to the diy community. I've got 10
things in my "modules to build some day" box and every one either
requires or would benefit from a microcontroller of some sort. It's
inevitable, there are just some things that just work better, or make
more sense, with an embedded processor.

At 7:36 PM -0400 2007/10/01, Richard Brewster wrote:

>At one time I intended to be a purist and not buy any module containing
>a microprocessor. Part of my reticence was due to the lack of kits in
>this genre. That didn't last long. First I bought an Encore Frequency
>Shifter. Then of course a MOTM-650. Added to my collection now are the
>Encore UEG, Modcan Dual Quantizer, Modcan CV Recorder, and, soon, the
>Modcan VCDO. Of course I want a Cloud Generator too! I probably
>represent a small customer niche, but what I like about such modules is
>that they sport analog-like user interfaces (the MOTM-650 not
>withstanding its menu system). I like being able to set up modules
>using knobs and buttons. I do not wish to hook up a computer to my MOTM
>to control it. (I did try it to get a MIDI soft sequencer going - oh
>the pain - the pain of trying to control my MOTM with a mouse.) If you
>wander on over to the Modcan website and check out the latest Modcan B
>module, you can see the analog interface trend being continued there.
>The Quad Envelope Generator 60B contains 4 digital envelope generators,
>each with 6 parameters. It's is programmed with 6 knobs and 3 buttons,
>with a few LEDs to keep track of where you are. I like that sort of
>interface! It is clean and simple, and powerful. Settings are saved
>between power cycles. So you have a small programmable module without
>any screen, even an LCD. I'm impressed. I like this trend, and I hope
>Paul takes note. I'm not opposed to an LCD if there is room. I don't
>mind embedded microprocessors. But you can see why I lurked silently
>over the thread about how to extend the Cloud Generator be controlled by
>USB, MIDI, Ethernet, Bluetooth and iPhone. Give me some knobs and
>switches. I'm old fashioned. I love to kick back and play without
>having to boot up a computer.
>
>If this seemed like a rant, it wasn't. There are many ways to control a
>synthesizer and using a computer is a valid one. I'm just offering a
>point of view.
>
>Richard Brewster
>http://www.pugix.com
>

a) the reality is: there are just a few things left to design using op amps
and OTAs (and OTAs are disappearing fast). And those designs tend to have a
LOT of individual parts. Which, quite frankly, I'm a little tired of :)

b) In the past, the "missing link" in what I will call 'digital core'
modules is the lack of inexpensive, but accurate, ADC and DAC ICs. If you
want to control MOTM VCOs accurate to pitch, you need a minimum of 14 bits
with about +-2LSB of INL. A 12-bit converter just is not accurate enough
(you need uV of error, not mv). And, you need accurate, non-drifting voltage
references to drive these.

Such parts have been around 5 years or so, but just *recently* been at a
price point that makes them a "no brainer". The ADC used to be the limiting
part, but now the ADC technology has surpassed the DAC side. Analog Devices
is touting (but not yet delivering) a family of 16-bit parts priced where
the 14-bits are now (that is 8 *times* better accuracy). I have been closely
following ADC/DAC price/performance trends (like I like to follow USB thumb
drives. I predict 16GB at $39 Christmas 2008).

The other factor is the introduction of literally 100s of ARM-based uPs.
These 32-bit, single-cycle parts can run up to 90MHz while having huge
on-chip memories (512K Flash for programs, 32K for data) and still be $10 in
100pcs. For $35 you can get ARM parts that run 220Mhz and can boot Linux :)
Smaller ARM parts are < $2! Gone are the clunky 8051 8-bit parts with
12-cycle instructions running 20Mhz (and costing $6). MicroChip PICs?
Meh......In fact, if one decides to play in "Buchla space" ($850 for a noise
generator? cough) then for $99 you can get an *entire* IBM PC clone on a pcb
that is the same size as a busines card and it runs 400MHz. With Ethernet,
USB and CF card reader.

c) It is easier to be 'clever' in SW than in HW. Check out the bazillions of
VST plugins. Look at the Buchla 200e.

d) My new tag line for 2008: 'Digital Done Right!' If you pick the *better*
parts, and do a *careful* pcb layout (6 layers is a good place to start)
then no one will "notice" what is behind the panel. Also, you need *good DSP
programmers* that understand how not only to code the product, but how to
code it *well*.

Paul S.

> At one time I intended to be a purist and not buy any module containing
> a microprocessor. Part of my reticence was due to the lack of kits in
> this genre. That didn't last long. First I bought an Encore Frequency
> Shifter. Then of course a MOTM-650.

I would *VERY* much like to see the MOTM-650 done in an all-analog form.
That would be super impressive - from both an engineering and a cost
perspective. ;-)

It is possible to do digital control that is indistinguishable from true
analog control but like Paul said, "digital done right". Sadly there are
a lot of implementations that are sub-par, causing many to believe that
digital control is the root of the problem.

"doing it right" requires a bit more up front design considerations to
ensure that enough precision is used, update rates to DACs are fast
enough, and cumulative/rounding errors don't enter in to the operation.

As an aside, when we did the 650 firmware, our goal was for the
"ridiculous" case. We wound up using 16.16 bit arithmetic for things like
portamento, which gives us a full DAC range sweep from anywhere from 3ms
to 149 days. That bit of resolution gives a VERY smooth portamento,
regardless of the rate in question.

-->Neil

----------------------------------------------------------------------------
C. Neil Bradley - KE7IXP - The one eyed man in the land of the blind is not
king. He's a prisoner.

At 08:01 PM 10/1/2007, Paul Schreiber wrote:

>... a family of 16-bit parts priced where
>the 14-bits are now (that is 8 *times* better accuracy)....

Okay, I'll play the straight man: Aren't 16 bits *4* times more
precise than 14 bits?

Then again, you said "accuracy", not "precision", so I'm -- ahem -- a
bit confused.
--
john


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Ack....4 times.

Paul S.
where's my Dr. Pepper?

>>... a family of 16-bit parts priced where
>>the 14-bits are now (that is 8 *times* better accuracy)....
>
> Okay, I'll play the straight man: Aren't 16 bits *4* times more
> precise than 14 bits?

At 11:05 PM 10/1/2007, Paul Schreiber wrote:

>Ack....4 times.

Aha -- I *knew* you were human! ;-)

>where's my Dr. Pepper?

You mean the soda with the commercial that has a "Welcome Back My
Friends" soundtrack?
--
john


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Hey Guys,"==== ALSO, I don't see the 16 bit ADC for VCO's..Paul S. mentioned. There is VCO stability--linearity--jitter--etc also... Why not use the DDO's that have microcycle resolution over a wide range- EVEN Freq or phase modulation !
-when driven by a proper instruction of a step-stored sequence word?? ( A MIDI variant.) Obviously, I need to know the problem better-- "

----- Original Message -----

From: Rob Johnson

To: Paul Schreiber ; motm@yahoogroups.com

Cc: Richard Brewster

Sent: Wednesday, October 03, 2007 5:19 PM

Subject: Re: [motm] Microprocessor trend in analog modules

Hey Guys,

I have a friend who is "not on the list" who is helping me with some tube based modules prototypes. He is much more technical than I as he worked at JPL back in the 60's when they were doing some interesting stuff (not that it's not interesting today) and has a good 30 years of experience on me. We have been talking about analog Vs. DSP for certain aspects of the modules we are thinking of making (don't want to say "what" just yet) so I FWD'd this thread to him and he had a question that I couldn't answer so I'm hoping one of you will be able to.

On Oct 1, 2007, at 5:01 PM, Paul Schreiber wrote:

b) In the past, the "missing link" in what I will call 'digital core'
modules is the lack of inexpensive, but accurate, ADC and DAC ICs. If you
want to control MOTM VCOs accurate to pitch, you need a minimum of 14 bits
with about +-2LSB of INL. A 12-bit converter just is not accurate enough
(you need uV of error, not mv). And, you need accurate, non-drifting voltage
references to drive these.

Such parts have been around 5 years or so, but just *recently* been at a
price point that makes them a "no brainer". The ADC used to be the limiting
part, but now the ADC technology has surpassed the DAC side. Analog Devices
is touting (but not yet delivering) a family of 16-bit parts priced where
the 14-bits are now (that is 8 *times* better accuracy). I have been closely
following ADC/DAC price/performance trends (like I like to follow USB thumb
drives. I predict 16GB at $39 Christmas 2008).

Chuck's response/Question:

"==== ALSO, I don't see the 16 bit ADC for VCO's..Paul S. mentioned. There is VCO stability--linearity--jitter--etc also... Why not use the DDO's that have microcycle resolution over a wide range- EVEN Freq or phase modulation !
-when driven by a proper instruction of a step-stored sequence word?? ( A MIDI variant.) Obviously, I need to know the problem better-- "

I will relay any responses to him and of course I'm just interested to know too.

Thanks!

Rob

That's what I was thinking but didn't really know for sure. Thanks Paul!