[sci.electronics] Digital Mixer Using Burr-Brown 200 Khz ADC

byron@pyr.gatech.EDU (Byron A Jeff) (09/23/89)

How difficult a proposition would it be to use this BB ADC to build a
multi-channel digital mixer? I haven't read the specs on it yet (I will
today at the Tech library) but if it's dual 200Khz ADC then it should
be possible to sample 8 audio channels at CD (44.1 Khz) or DAT (48 Khz)
quality. So how feasible is something like this:

-----------  ---------  ---------  --------   --------  --------  --------
|8        |--|Analog |--|Filters|--|      |   |      |  |      |  |      |
|Audio    |--|Multi- |  |  and  |  | ADC  |---| DSP  |--| DAC  |--|Filter|
|channels |--|plexors|--|  S/H  |--|      |   |      |  |      |  |      |
-----------  ---------  ---------  --------   --------  --------  --------

With the output being either high quality audio or DAT compatable digital.
The DSP would handle all mixing, EQ, effects, etc.

If samples can be obtained for ~$50 then a box for between $200 to $300
could be realized. If the DSP is fast enough then another ADC could
easily be added for a grand total of 16 channels.

Any comments? Most of the info I have is from "Musical applications for
Microprocessors".

Crossposting is for exposure. 
Redirect the discussion to the appropriate newsgroup.

comp.dsp - Role of DSP processor/algorithms in such a system.
sci.electronics - electonic aspects (analog filters, S/H, ect)
rec.music.synth - applications (for example midi control for setting
mixer/effects parameters, midi controled fades, and the like.)

BAJ
-- 
Another random extraction from the mental bit stream of...
Byron A. Jeff
Georgia Tech, Atlanta GA 30332
Internet:	byron@pyr.gatech.edu  uucp:	...!gatech!pyr!byron

byron@pyr.gatech.EDU (Byron A Jeff) (09/28/89)

[This is a repost. I got absolutly no response to the first posting.]

How difficult a proposition would it be to use this BB ADC to build a
multi-channel digital mixer? I haven't read the specs on it yet (I will
today at the Tech library) but if it's dual 200Khz ADC then it should
be possible to sample 8 audio channels at CD (44.1 Khz) or DAT (48 Khz)
quality. So how feasible is something like this:

-----------  ---------  ---------  --------   --------  --------  --------
|8        |--|Analog |--|Filters|--|      |   |      |  |      |  |      |
|Audio    |--|Multi- |  |  and  |  | ADC  |---| DSP  |--| DAC  |--|Filter|
|channels |--|plexors|--|  S/H  |--|      |   |      |  |      |  |      |
-----------  ---------  ---------  --------   --------  --------  --------

With the output being either high quality audio or DAT compatable digital.
The DSP would handle all mixing, EQ, effects, etc.

If samples can be obtained for ~$50 then a box for between $200 to $300
could be realized. If the DSP is fast enough then another ADC could
easily be added for a grand total of 16 channels.

Any comments?

BAJ
-- 
Another random extraction from the mental bit stream of...
Byron A. Jeff
Georgia Tech, Atlanta GA 30332
Internet:	byron@pyr.gatech.edu  uucp:	...!gatech!pyr!byron

mark@mips.COM (Mark G. Johnson) (09/28/89)

In article <9231@pyr.gatech.EDU> byron@pyr.gatech.edu.gatech.edu (Byron A Jeff) writes:
>[This is a repost. I got absolutly no response to the first posting.]
>

Maybe that's because gatech.edu is bouncing email back to senders.
For example, I myself got:

Returned mail: Service unavailable
While talking to gatech.edu:
>>> DATA
[... lots more poop ...]

   ----- Unsent message follows -----

I suggest that when you're building it, and afterward when you're
debugging and testing it, be sure to measure the actual observed
performance of the Burr-Brown part.  Compare this to the datasheet;
is the datasheet dead-on, wildly optimistic, or conservatively pessimistic?

This will help other readers of these Newsgroups decide whether or
not to use the BB device in their own projects.
-- 
 -- Mark Johnson	
 	MIPS Computer Systems, 930 E. Arques, Sunnyvale, CA 94086
	(408) 991-0208    mark@mips.com  {or ...!decwrl!mips!mark}

schabtac@porter.uucp (Adam Schabtach) (09/28/89)

In article <9231@pyr.gatech.EDU> byron@pyr.gatech.edu.gatech.edu (Byron A Jeff) writes:
>[This is a repost. I got absolutly no response to the first posting.]
>
It's possible you got no response because your first posting was a bit
vague.  For instance, it would help if you told us which chip you have
in mind -- that is, give us the part number (BB makes quite a few
ADCs :-).  I'm assuming you're talking about the chip that was featured
on the cover of a recent electronics trade journal.

>How difficult a proposition would it be to use this BB ADC to build a
>multi-channel digital mixer? I haven't read the specs on it yet (I will
>today at the Tech library) but if it's dual 200Khz ADC then it should
>be possible to sample 8 audio channels at CD (44.1 Khz) or DAT (48 Khz)
>quality. So how feasible is something like this:
>
> [ diagram showing ADC->DSP->DAC deleted ]

It depends on what you mean by "difficult" -- i.e. how are you with digital
prototyping?  The circuit you describe would require a lot of work to get
together, debugged, and running.  (I think I can generalize that way and
say that almost anyone would consider it "a lot" of work, even if they
worked for Fairlight or some place like that.) 

As far as using the ADC for 8 channels, from skimming the aforementioned
article, it seemed to me the chip was best suited for just doing two
channels.  It could be set up with a multiplexer, but since it's pretty
cheap (under $30 in lots of $1000, so probably under $50 to you and me), 
you would probably save yourself time and frustration (and hence money) by 
using several chips instead of a multiplexer.
>
>With the output being either high quality audio or DAT compatable digital.
>The DSP would handle all mixing, EQ, effects, etc.
>
You'd probably end up using several DSPs.  It demands most of the processing
power of one current DSP chip (say the Motorola 56000) to implement a
fairly complex reverb, OR a graphic EQ, so if you wanted EQ, effects, etc.
for each channel, I think you'd end up using at least one DSP per channel.

>If samples can be obtained for ~$50 then a box for between $200 to $300
>could be realized. If the DSP is fast enough then another ADC could
>easily be added for a grand total of 16 channels.
>
Um, I think you're underestimating a bit.  The socket for a 56000 costs about
$20, and it looks like you'll need at least 8 of those.  That's $160.  Etc...
Don't forget to throw in your own personal cost in design, labor, debugging,
etc.
>Any comments?
>
There they are.  I don't mean to be discouraging, but it sounds like a pretty
big project (albeit very interesting -- I wish I had the time to tackle 
something like it).
--Adam                    *  *  *  KILL YOUR TELEVISION  *  *  *      
schabtac@stout.ucar.edu      

ivan@megatest.UUCP (Ivan Batinic) (09/29/89)

	I like your idea...  I am not an expert in this area, however
I feel the problem would be in post-processing; i.e. the DSP
processing rate would have to be very high.  May I suggest that you
repost (again) to the newsgroup 'comp.dsp' (recently introduced) They
are talking up a storm about audio dsp applications.

	Good luck, and please email me any responses -- I am
interested.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Ivan

ivan@megatest.UUCP (Ivan Batinic) (09/29/89)

	Had I bothered to notice the distribution list, I would have
realized that you DID infact post this (as did I) to the newsgroup
'comp.dsp'  -- My sincere apologies you and this newsgroup!

	Ivan

rahardj@ccu.umanitoba.ca (Budi Rahardjo) (09/29/89)

>From alberta!ubc-cs!uw-beaver!cornell!mailrus!cwjcc!gatech!gitpyr!byron Fri Sep 29 00:29:20 CDT 1989
>[This is a repost. I got absolutly no response to the first posting.]
>How difficult a proposition would it be to use this BB ADC to build a
>multi-channel digital mixer? I haven't read the specs on it yet (I will
>today at the Tech library) but if it's dual 200Khz ADC then it should
>be possible to sample 8 audio channels at CD (44.1 Khz) or DAT (48 Khz)
>quality. So how feasible is something like this:

-----------  ---------  ---------  --------   --------  --------  --------
|8        |--|Analog |--|Filters|--|      |   |      |  |      |  |      |
|Audio    |--|Multi- |  |  and  |  | ADC  |---| DSP  |--| DAC  |--|Filter|
|channels |--|plexors|--|  S/H  |--|      |   |      |  |      |  |      |
-----------  ---------  ---------  --------   --------  --------  --------

Any comments?

I've questions :
What type of Analog Multiplexors ,Filters, S/H are you going to use ?
Are they fast enough ?
How do you control the mixer ? By modifying parameters of the DSP ?
Can you control each channels ?
Are you going to store /buffer the data in RAM before process them
with the DSP or just pass them thru ?
Well your design is possible, but I don't think that's an easy job..

Budi

byron@pyr.gatech.EDU (Byron A Jeff) (09/30/89)

In article <1989Sep29.054029.1605@ccu.umanitoba.ca> rahardj@ccu.UManitoba.CA (Budi Rahardjo) writes:
>> [This is my diagram]
>>-----------  ---------  ---------  --------   --------  --------  --------
>>|8        |--|Analog |--|Filters|--|      |   |      |  |      |  |      |
>>|Audio    |--|Multi- |  |  and  |  | ADC  |---| DSP  |--| DAC  |--|Filter|
>>|channels |--|plexors|--|  S/H  |--|      |   |      |  |      |  |      |
>>-----------  ---------  ---------  --------   --------  --------  --------
>
>Any comments?
>
>I've questions :
>What type of Analog Multiplexors ,Filters, S/H are you going to use ?

My understanding from a previous message is that the S/H is built in.
As for analog multipexors and filters I'm an ingnorant novice looking
for reccomendations. Any suggestions?

>Are they fast enough ?

I don't know.

>How do you control the mixer ? By modifying parameters of the DSP ?
>Can you control each channels ?
Through MIDI for me. I'm in the process of building the ultimate Midi-Merger,
sequencer, drum machine and adding mixer control is no problem. I'm am a
novice to DSP (that's why I read the newsgroup with great interest) but
with a M.S. in C.S. I think I can handle the programming and the math.
Modifying the DSP parameters through MIDI is the plan. How much control
over each channel I get depends on the processing power (I figure I'll get
this in a bit when I get to comp.dsp) but having individual channel control
would be desirable.

>Are you going to store /buffer the data in RAM before process them
>with the DSP or just pass them thru ?

Again it depends on the speed of the processor and the types of effects
I'm trying to get. I figure I may have to buffer a bit (up to 16K x 24 bits)
but I don't perceive that as a real big problem.

>Well your design is possible, but I don't think that's an easy job..
That's the kind of data points I'm trying to gather. If I can put it together
in a handful of weekend for $250-$300 (simplified by the fact I have
access to a DSP evaluation board) then I'll do it. Otherwise I'll leave
it to some genius to do. I'm looking at it just as a hobby project.

>Budi

Thanks for the comments. Keep 'em coming!
BAJ
-- 
Another random extraction from the mental bit stream of...
Byron A. Jeff
Georgia Tech, Atlanta GA 30332
Internet:	byron@pyr.gatech.edu  uucp:	...!gatech!pyr!byron