MIDI-CV converters (was: Building my first synth...)

[gstopp at fibermux.com]

     Well I wuz thinkin' about this some more...
     
     See we gots too many PCs lying around at home. My wife is a serious PC 
     head (she writes token ring drivers fer chrissake's) and she HATES the 
     fact that I have an old XT with a CGA monitor WASTING space on the 
     shelf. She wants me to donate it to a school for the tax writeoff or 
     put bulbs (the plant kind) in it or something. Give her a Pentium or 
     give her death. Even my Mac's in storage right now (what THAT 
     glorified video game?).
     
     But I look at the old XT with fond memories of Texture and Personal 
     Composer and hacking out my own MIDI datascope programs and random 
     MIDI message generators and all that fun stuff from my pre-marital 
     party days. It has a perfectly good first-generation MPU-401 in it and 
     hey - it's in good running condition. So I thinks - perfect MIDI to CV 
     development platform! All I need is some D/A output hardware.
     
     Here's my list of potential approaches:
     
     * D/A card in PC slot - minimized throughput bottlenecks
     
     * Sample/hold updated single D/A converter - cuts D/A cost
     
     * No sample/holds, one D/A per CV - more D/A cost, simpler
     
     * D/A card on parallel port - some reduction in throughput
     
     * D/A card on serial port - even more reduction in throughput
     
     * CPU-updated sample/holds - no shared RAM required
     
     * Sampled/holds updated by shared RAM - offloads CPU
     
     I do have some concerns about D/A accuracy. I have had a lot of 
     success with driving an R-2R ladder with a CMOS-output latch, and less 
     success with single chip D/A's, at least for CV generation. However 
     this was years ago and things may be a lot better these days as far as 
     the chip solution goes. Time to pound the databooks I guess.
     
     If the hardware were to use the serial port for computer control, then 
     it would be cross-platform compatible (Atari, Amiga, Mac, etc.) at 
     least from the hardware angle.
     
     Anybody recommend a good book on IBM PC bus architecture, address and 
     databuss access, and parallel port signalling?
     
     Hey maybe I can get my wife to write the driver.
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: Re: MIDI-CV converters (was: Building my first synth...)
Author:  Christopher List <Christopher_List at sonymusic.com> at ccrelayout
Date:    2/6/96 7:30 AM
     
Sounds brilliant, Gene! I don't know why, with all these companies (OK, so 
there's only 1 or 2 of 'em) making MIDI to CV converters, someone hasn't already
done this! In fact (total brain storm here) a sound card with an amplifier could
be used as a one-channel midi-CV converter - Left for the gate, right for the 
CV... - Sorry, I'm getting crazy... 
     
Back to the original topic. The cool thing would be to have a utility type 
program that could run on your PC or Mac which commandeers the parallel port and
one of your MIDI output ports. The utility would have a little patch-bay kinda 
setup thing, like all device drivers, and could route the midi data from one (or
more?) midi out ports to the various CV channels. - Then you could just route 
your sequencing software to the out-port assigned to the converter - or use midi
mapper to route an input port to the converter output port. I bet the software 
would be totally easy to write and could have all kinds of features that would 
be a real drag to put into a hardware-based Midi-CV converter. 
     
Now THIS is a seriously marketable product! 
     
Unfortunately, I've never done any device driver or serial / parallel port 
coding. Although I've seen some decent books on the subject.
     
I gotta go on some kind of "Unlimited Power" wheat-grass juice diet plan or 
something so that I can get by on only 3 hours of sleep a night and work on all 
these projects (sigh)...