Re: [AH] digital oscillators & clocks

From Brian Willoughby
Sent Thu, Jun 7th 2018, 06:51

On Jun 4, 2018, at 2:57 PM, Kenny Balys <xxxxx@xxxxxxxx.xxx> wrote:
> Perhaps one could say the transition to interpolation happened with =
the release of the Ensoniq Mirage in 1984. It was probably cheaper to =
let the CPU do the work than have a cascade of logic dividing down clock =
frequencies.

It=E2=80=99s a little misleading to describe the Mirage this way, but =
you=E2=80=99re probably correct that the Mirage changed everything.

The Mirage operating system runs on a 6809, which is a fairly standard =
8-bit processor. But that little processor hardly processes samples on =
its own. Ensoniq also designed custom ASIC chips, although I=E2=80=99m =
not sure about the names. The Mirage FAQ mentions the Q-Chip while the =
Wikipedia page mentions the Digital Oscillator Chip (Ensoniq ES5503 DOC) =
that later appeared in the Apple //gs. These custom chips have way more =
than "a cascade of logic dividing down clock frequencies,=E2=80=9D and =
they=E2=80=99re the real reason that the Mirage was so affordable.=20

The DOC was designed by Robert Yannes, who had designed the SID chip. =
Ensoniq followed up with the ESP (Ensoniq Signal Processor). At one =
point, IBM was in discussions with Ensoniq about licensing the ESP as a =
future IBM DSP, but the deal fell through. These were separate from the =
required DAC chips.

Basically, the experience of making affordable home computers like the =
Commodore-64 are what allowed us to enjoy a serious advancement in =
sampling sound.

I=E2=80=99m a bit more familiar with the ESP, because it is available on =
the Ensoniq Soundscape cards and was fairly well documented. Some =
sources refer to it as having an instruction set, but I don=E2=80=99t =
know whether that was ever exposed to customers. The Soundscape allowed =
access to registers that controlled various aspects of sampled voices, =
but I don=E2=80=99t recall an assembler or compiler. I have the =
documentation around here somewhere, but I=E2=80=99m going from memory =
on this.

The modern equivalent of the Mirage would probably be based on an FPGA =
plus a general purpose CPU for the main operating system. The FPGA would =
be able to handle the dense logic that used to require an ASIC.

Brian Willoughby
Sound Consulting