[sdiy] Wavetable info

[Rainer Buchty]

> I forgot to mention the ESQ-1 waves originally at 1024 bytes / 8 bits.

They're usually only 512 bytes, IIRC. With the SQ80 (ESQ1's big brother)
you find a variety of wave sizes. Theoretically, size can be anything
between 256 and 32768 bytes as the sound chip supports discrete wave sizes
of 256, 512, 1024, ..., 32768 bytes.

The interesting part here is that samples *must not* contain the value
0x00, i.e. they are absolutely symmetrical from -127 to +127. 0x00 is used
as an "end of sample" tag. If the DOC (Mirage, ESQ1, and SQ80 sound chip)
finds the value 0x00 in the sample stream (the data sheet suggests at
least 8 consecutive 0x00) it stops playing back (and might restart or
trigger the sibling oscillator, see below, in case of looped or chained
mode). Doing so, it can play back any wave size up to 32768 bytes (which
is the maximum length for a single wave). For bigger waves, two "sibling"
oscillators can be daisy-chained allowing a maximum wave length of 64kB.

Rainer