Re: [LAU] Cubase64

2010/10/6 Robin Gareus <robin@email-addr-hidden>:
> On 10/06/10 13:57, Andrew C wrote:
>> Actually, I could've sworn that the SID had 3 voices with independent
>> oscillators and a 4th sort of 'audio' channel due to some sort of
>> memory glitch or such? I'm not sure of the specifics.
>> Andrew.
>>
>
> The trick was/is to output noise through one of the voices and use the
> master-output gain to 'fake' PCM. I guess that's how "Cubase64" works.

From the white paper:
"The Commodore 64 has a sound chip that wasn't designed for
playing samples. Since there's not much available memory,
they did not intend the SID chip to play samples - 64kB with
8kHz sample rate will give you a some 8 seconds of sound to
play. There was no need for sample playback.

So, we have to fool the SID chip to play samples, even
though it only has the means of playing either a continuous
triangle waveform, sawtooth waveform, pulse-width waveform
or noise waveform. This is done by using the triangle
waveform, resetting the oscillator with an undocumented testbit
originally implemented for factory testing, setting the
accumulator frequency to change the increment speed of the
accumulator, and then after an exact number of clock cycles
enable the triangle waveform output just briefly, practically
emulating a sample-and-hold filter that will keep the analog
output fixed at a certain voltage."

/Robert
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Received on Wed, 6 Oct 2010 14:59:10 +0200