Re: [stella] New idea for 6 channel music on the 2600

Subject: Re: [stella] New idea for 6 channel music on the 2600
From: "Thomas Jentzsch" <tjentzsch@xxxxxx>
Date: Wed, 19 Sep 2001 12:48:16 +0200
Kevin wrote:
> I have an interesting idea for generating 6 channel music using nothing but 
> a stock 2600.  The basic idea is to use the two volume registers on the 
> chip to generate 3 channels each.

What's the reason for the 6 channels? Is it due to hardware restrictions, or don't you just have enough cycles to do more? 

> It appears that I can generate square waves, ramps, and triangle waves in 
> this fashion, mix them in software, and then output their values to the 
> volume registers with just enough time to spare.  The only downside is 
> there can be no video while this is occurring (except for maybe flashing 
> the screen or some other relatively static display).

How do you mix 3 channels into only 1 register? I'm sure there must be some info in the web how this works, could you provide some links, please?

> The basic idea for this is to increment a phase accumulator for each 
> channel every scanline and use the upper bits of it to select bytes from a 
> waveform table; then add them to an accumulator, and finally output the 
> results to the sound volume registers.

That does also mean, that you are generating the frequency too, right?
Hey, then we would be able to play REAL notes with correct frequencies on the 2600!

> I already have some basic code written for this, and should post more about 
> it in a couple days.  Unfortunately, due to cycle constraints, this thing 
> will only work for linear note/length/instrument data, and cannot use a 
> track/pattern/note setup (which I originally wanted to use).  There's just 
> not enough cycles otherwise.

If you post it, unless the code is to simple, I'm quite sure, the members of the list will be able to find cycles :) 

> Would such a piece of code be at all useful?  I was thinking maybe a 
> power-on tune, in between level tunes, etc.  It may be possible to 
> "multiplex" the sound updating every couple scanlines with some TIA 
> updating, but I dunno yet if this will be possible to do.  This code as it 
> stands is very very cycle-intensive.

Of course it's useful! 

> Thoughts? Comments?

Cool, I can't wait to see this! 
Maybe by reducing the number of channels, we could also be able to mix graphics and sound. 

I hope, at least one of the emulators (z26?) will procude that music...

Have fun!
Thomas Jentzsch         | *** Every bit is sacred ! ***
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