gripes and more on cheap sampling

Mikko Helin MHELIN at tne01.tele.nokia.fi
Fri Jan 30 11:22:46 CET 1998


Hello.

I checked the data sheets on www.isd.com, these voice chips are
actually multi-level analog eeproms, no A/D conversion is used.
Sampling rate seems to be 8 kB/sec maximum, so this limits
the frequency range to 4 kHz, not good for those break beats.

I've got an extra 486DX4-120 motherboard, and I've been thinking 
how it could be used for something useful. I know how to set it so
that all the extended memory could be accessed in  real mode
with 32-bit pointers, without any DOS extenders. It would
make a really nice sampler with some decent quality sound card -
maybe it would be even possible to synthesize some virtual analog
voices at the same time. There seems to be quite a many sound
cards with CS4237B codec, which got also the S/PDIF output,
so that would be a good choice for sound card, and you get the
MIDI for free, as well as a joystick port (the S/PDIF output
port takes the other game controller out of use). If you stick
in a multi i/o adapter you get an IDE and a floppy controller, 
couple of RS-232 ports and a printer port. You don't need the keyboard
or monitor if you make the programs to use the RS-232 port for 
input and output (this can be made with DOS MODE -command) - just
connect the thing to your other computer and use the Windows
Terminal program to access it. You can cope with a 1.44 MB floppy
disk, or install a HD (nice for samples). This thing doesn't take
that much space, and can be installed on the rack if some 19"
industrial PC case is used. A +/- 12V linear PSU would be nice
for the sound card (for a better SNR), of course an external
S/PDIF DAC would be better.  

The software is the hard part, a real multi-tasking DOS would be 
better as you could run multiple apps at the same time, like a DCO 
in one session, a DCF in other and a DCA in the third. This would be 
really nice if you later replace the 486 with Pentium, which got 
much more processing power. With 486 the usual real mode DOS is
better, but limits the use somehow - every function must be
programmed into the same program, and even if you can use
several MB's for data, the program must fit in 640 kB.

---
Mikko Helin


>
>Although it's not strictly synthesizer-related, I remember a while ago
>people asking me about the project I was working on involving cheap little
>toy samplers... I've moved on a bit and found a little chip at radio shack
>called the ISD1000A. Really nifty, and it's triggered by a momentary +5V
>connection, which means you can use trigger outs or a gate signal to play
>samples. (ah! finally a sign that it might be useful!) The only drawback
>is you have to have some sort of battery-backed system lest you loose your
>samples... so at best it's a plaything or studio item. It does however
>have 20 seconds of sample time, and you can choose the sampling address
>pretty easily with an 8 position DIP switch. (I'm just using 8 SPDT
>switches probably for easy of twiddling) It also has a looping option...
>hmmm... maybe the latest DJ-hyped-wassamajigger toy? 
>
>I plan on putting a filter of some type at the output of mine. There are
>no schematics needed for the sampler really, since a full spec packet
>comes with the chip. (BTW i think it's regularly 17.99, i think i got it
>on sale for 14.99 or somesuch, which means you can have a little sk-1 type
>sampler up and running for at most $25 if you toss in the cost of a spiffy
>plastic box) And one last thing... you can hook 'em together in parallel
>for more sampling time... heh, I kinda hope somebody goes to buy a lot of
>a dozen to hook together just to prove it can be done, although I'm sure
>the sound quality is nothing to go nuts about. 
>
>Andrew
>NP: Autechre, "Chichlisuite"
>



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