80186 and now AMY chip

From: John Foust <jfoust_at_threedee.com>
Date: Thu Nov 16 08:31:39 2000

At 04:54 PM 11/10/00 +0000, John Honniball wrote:
>Absolutely. It was just like an 8086, as far as the
>programmer was concerned, but it had a few on-chip
>peripherals.

The threat of being asked to program the 80186 in assembler
all day long played a major part in my decision to quit a
job back in 1985 or so. I knew my brain would melt, so I
became a freelance writer in the Amiga market.

If I'd stayed, I would've been doing low-level programming for
a box the company was developing - a digital additive
synthesizer MIDI rack-mount based on the Atari AMY chip we'd
bought from the Tramiels. Previously my work had been in C
on sound analysis and MIDI software.

The AMY chip was one of the pieces of flotsam that was
sold as Atari Games crashed and burned. The AMY chip
produced a digital audio stream by digitally summing sine
waves from its ROM look-up table. It had 64 digital
oscillators, essentially. Each was programmed with
slope and destination: get to this amplitude in this
amount of time. As such, it was an extremely low bit-rate
device, in sharp contrast to other dedicated audio chip sets
that needed either large amounts of RAM for samples or
more frequent attention from a processor or coprocessor.

I'm still struck by the similarities of this method and
today's MP3 encoders, which have at their core of tricks
the same sort of frequency analysis on short segments of sound.

In one experiment I remember being able to recreate
telephone-quality voice audio at a bit rate that could be
pushed through a 2400 baud modem. We could analyze and store
a sound such as a sampled piano key strike in just a few K,
and it was pitch independent. (Of course, for a very
faithful piano sound, we'd sample a key in each octave or so.)

- John
Received on Thu Nov 16 2000 - 08:31:39 GMT