[sdiy] Fwd: DX7 chip die photos

[Anthony]

I just found this mailing list through a comment left on Ken Shiriff's article. I corresponded with Ken to provide a little bit of background technical information on the DX7. I wrote an article with some technical details that he links to in his article: https://ajxs.me/blog/Yamaha_DX7_Technical_Analysis.html
I can try to answer some of the questions raised in the thread.
> So with a bit more “oomph” in the support processors, the DX7 could have been multitimbral? Interesting possibility!

I wish this was the case! Unfortunately as far as we know, the OPS chip only has a single register specifying the algorithm, and oscillator sync settings for all voices. I've been going through the firmware looking for any hidden features, and unfortunately I don't think the synth can be changed in any significant way via the software.

> Or maybe they designed into the chip but it didn't work for some reason ?

My guess is that the design evolved over time from Yamaha's early FM synthesisers. They may have intended to add multitimbrality to them at one point, and then abandoned it because of the cost, or complexity.

> The algorithm yes, but what about all the other parameters? Could these have different values for the 16 notes too?

Most of the synth's parameters are 'global', unfortunately. The only per-voice setting the EGS chip supports is operator volume. Being able to alter the operator pitch on a per-voice basis would be required for any kind of useful multitimbrality.

> how is it that any of the Yamaha FM operators close their envelopes off to zero amplitude?

For at least some of the amplitude parameters, a value of 0xFF indicates zero. I distinctly recall that the operator volume value sent to the EGS chip uses 0xFF to indicate a zero amplitude.

Incase anyone was wondering, the parts of the synthesis process performed on the CPU are portamento/glissando, LFO, pitch, and amplitude modulation. These modulation inputs are aggregated and sent to the EGS chip's global amplitude, and pitch modulation registers. Portamento/Glissando just alters the voice pitch, which is sent to the EGS' per-voice pitch registers.

Kind regards,
Anthony
‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Thursday, November 18th, 2021 at 10:16 PM, Ben Stuyts <ben at stuyts.nl> wrote:

>> Begin forwarded message:
>>
>> From: Mike Beauchamp <list at mikebeauchamp.com>
>> Subject: [sdiy] DX7 chip die photos
>>
>> Date: 13 November 2021 at 19:00:20 CET
>> To: "synth-diy at synth-diy.org" <synth-diy at synth-diy.org>
>>
>> I just saw this on the internets:
>>
>> https://www.righto.com/2021/11/reverse-engineering-yamaha-dx7.html
>>
>> full res pic: https://static.righto.com/images/dx7/die-labeled.jpg
>>
>> Mike
>>
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