Need help with Philips SAA1099 sound chip.

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Submitted by madaxe on Wed, 02/19/2020 - 18:08

 

Hi everyone!

I'm making some tests with the SAA1099 and I can produce lots of sounds but I can't set the envelope duration. I have tried different values for frequency and octave of the channel 2 (I assume a 0-5 channel number) and in fact the length of the envelope varies but it's always very short. There is any way to produce long length envelopes like we do in AY-3-8912?

By the way, what is the meaning of the bit 5 (external/internal clock) and bit 4 (16/8 bit resolution) on the envelope registers?

Note: I am using SimCoupe and DOSBox with the Game Blaster option.

Thanks in advance,
José Mário aka Madaxe.

 

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ascii Mon, 02/24/2020 - 13:45

The speed of the envelope on channel 2 is controlled by the frequency generator of channel 1 - the two channels operate in conjunction. To get a purely sawtooth waveform this means you want to use zero volume in channel 1, but you can experiment getting some interesting sounds if you let them play together and interact.

Bit 4 controls how many wave edges on channel 1 will complete a wave in channel 2. Mainly the audible effect of this is to double or halve the frequency (that is, if it's in a note range, change it up or down by one octave).

Not sure about bit 5, it's probably not useful in the Sam (I guess it's for compatibility with systems which wire the chip up differently.) I've always left it at 0.

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madaxe Tue, 02/25/2020 - 12:59

Thanks for your great explanation, it really helped :)

By the way, can you provide me two or three examples of envelope generator, something simple like REG,DATA?

Best regards.