Re: Crystal's new chip

At 01:55 PM 7/7/97 -0500, you wrote:

<snip talk of using a synthesizer chip as a sound board>

> This would work for anything which uses periodic waves (most sounds.)
>The Cinematronics stuff is a pain, most specifically the Background noise
in >Star Castle, etc. It has a different motherboard interface, which
basically
>sets the frequency of the background noise, rather than just being a "Loud
>Explosion Enable," etc like all the other sounds are.
>
> This remains to be seen, though, and by just increasing the rate that
> you step through the wave table, as a function of those motherboard inputs to
> the soundboard, I might be able to even get the background sound this way.
>This would probably involve using a PLL as the off-chip oscillator.

I don't have a schematic in front of me, but I thought Star Castle used one
of those "4 pin" shift registers. I don't remember them having an adjustable
clock speed. I thought it was done internal to the chip.

There is an adjustable frequency, on Star Castle, it changes the frequency
of the background drone. I think it's done with a simple resistor DAC going
into a VCO, though I know some games used a digital divider (Boxing Bugs).
Either way you *could* just sample the 16 (or so) different frequencies.

The beauty of a synthesizer chip, is that it can play a sample at different
"note" values, not to mention the MIDI "Pitch Bend". I believe you could
get by with one sample of either noise or oscillator. Through note changes
and pitch bends you should have nearly unlimited control of the
"frequencies". All the PLL stuff is built into the synthesizer, along with
all the wavetable control. There's nothing left for the PIC but "Play this
sound, at this note, with this pitch bend, with this ADSR envolope". Very
cool, very simple.

<snip>

-Zonn
Received on Mon Jul 7 13:05:53 1997