[sdiy] Old Computers

[Scott Gravenhorst]

=?ISO-8859-1?Q?Johannes_=D6berg?= <johannes.oberg at gmail.com> wrote:
>I (who wrote a couple of months ago about my semi-on-going project of
>building a sampler/groovebox out of a industrial PC-on-a-card and an
>AWE32 or GUS) am still interessted in some sort of collaboration; of
>making an opensource modular "os" for this type of synth. If anybody
>out there is interessted.
>
>Anyway, from experience, if you are using an old computer like a 486,
>you'll want DMA for the sound. LPT DAC won't sound very good, 

Why?  

This is essentially what the AVRSYN does.  I plan to do something very
similar, but I will add double buffering to eliminate the data skew.  I
may go the AD660 route if I can get free samples, otherwise, I'll build
it from four 8 bit latches and an R2R like Jarek's.

>but
>still, if you want something simple and mono, you can crank out 12
>bits with just a simple R2R network at a reasonable rate IIRC.
>However, too much processing power will go to the DAC service, so
>your synth engine will suffer. Also, you can get a pretty good
>multichannel MIDI interface via the LPT, which IMHO it is better
>suited for.

I don't see loading 2 ports and toggling a "load DAC" line as very much
processing at all.  But I will find out.  I plan a DAC update rate of
44KHz using the built in programmable interrupt timer.  This is a bit
faster than the 31.25 KHz of the AVRSYN.

The first cut will be very simple, certainly a mono-synth.  I will
build it on a 5x86-133 which would seem to have between 2 and 4 times
the power of the AVR used for AVRSYN.

I also have boxes running up to and including 500 MHz which I may use
when I try to play with polyphony.

My OS will be DOS (I know, I know, but I ain't changing), it's
something I have and I also have both C and assembler tools for DOS
based programs.

All I need for this is to make a DAC dongle - and it will plug into ANY
computer I have.

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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