[sdiy] Formant filters, yay!

rsdio at audiobanshee.com rsdio at audiobanshee.com
Sun Mar 12 03:05:14 CET 2017

On Mar 11, 2017, at 1:23 AM, Tony K <weplar at gmail.com> wrote:
> All this talk of vocal filters made me nostalgic for S.A.M. in the Apple ][+ playing through a 1408 DAC board.
> I don't have have Chamberlain's MAM anymore but I believe there was  a good coverage of the topic in there . I seem to recall VOSIM software.
> Would have loved to know who wrote that original Apple program.
> The later Atari version of SAM was also good but never quite sounded as impressive or 'demented' as the Apple version. Used that as my first drum machine in phoneme mode.
> Sorry if this is completely irrelevant.

It seems quite relevant for DIY Synthesis - at least it was for my experience. It even seems relevant, still, in terms of today's embedded audio synthesis platforms.

The Apple ][+ community seemed to be 99% piracy. People had no qualms about photocopying the manual and duplicating the disks. I never actually did this for myself, because I never actually saw any original software packages, and yet people often volunteered to give me copies when I was young. The strangest was when someone copied the S.A.M. manual and disk for me, because I realized that the software was useless without the hardware.

Fortunately, the last few pages of the S.A.M. (Software Automatic Mouth) software has the schematic for their hardware. I hand-etched a double-sided Apple ][ peripheral card with the DAC and op-amps and managed to get the thing working!

The S.A.M. vocal synthesis was reasonably interesting, but I quickly found that I preferred writing non-vocal audio synthesis algorithms for myself. I ended up with a linear FM program that was quite impressive (but only one voice of two operators). The analog output was a couple of watts, so it could directly drive a large speaker without an amp.

I would also like to know who wrote the original Apple S.A.M. software. Perhaps I can find the ancient photocopy of the manual and look for the author's name, if it's even mentioned in addition to the software company name.

You are correct that Chamberlain's "Musical Applications of Microprocessors" includes a chapter that covers VOSIM. It's Chapter 13, Digital Tone Generation Techniques, in the final section for "other," and it literally stands for VOcal SIMulation. I never realized that VOSIM is related to FM - not in exact technique so much as similar processing complexity.

Later voice simulators seemed to be based on dedicated chips where there was no direct access to the DAC. By being exposed to S.A.M. and building the DAC board, I was able to learn a lot more about digital audio synthesis on my own (I didn't read MAM until decades later). Of course, several years later computers like the Amiga had 8-bit DAC features built in, and the Apple //gs actually included the Ensoniq ESP chip, but by that time I had moved on.

Brian Willoughby
Sound Consulting

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