Re: [stella] Announcing "webTune2600"

Subject: Re: [stella] Announcing "webTune2600"
From: "B. Watson" <atari@xxxxxxxxxxxxxx>
Date: Sat, 13 Aug 2005 12:05:23 -0400
On Fri, 12 Aug 2005, Doug Dingus wrote:

> I did this long ago on the 8bitters. It's true @ 60Hz you will hear it. You
> hear it up to fairly high frequencies. What happens is the ear translates
> these into extra notes or it's heard as a pitch shift happening rapidly if
> the frequency is low enough.

I was afraid of something like that...

However... if I'm shifting at 60Hz, what's the extra note being heard? A
60Hz tone? What if I use a tuning where 60Hz is an in-tune note (it's
between a B flat and a B... I used to know a guy who tuned the B on
his guitar to the 60Hz hum coming out of his crappy amp, and the rest
of the guitar to that... it was the only way to make music instead of
noise come out of that amp).

Bleah. Even if that works, I wouldn't be able to play a normal
bassline. The 60Hz B's would clash with anything else in the bass.

> One thing that does work fairly well is to alternate the pitches every
> cycle. --with some pattern, 112112112, 121212121, etc... Let each tone run
> for exactly one cycle, then start the other one. I'm not sure the 2600 has
> the muscle to actually get this done however.

Not every CPU cycle... could use a hard-coded string of STA/STX and do
it every other cycle. Of course, that's *all* the 2600 would be doing
(no graphics, no game...)

Hmm, Manuel was talking about volume-only sound for playing 4-bit samples.
How often do you have to update the volume register to make anything sound
halfway decent? If every other scanline is enough (60 frames * 262 lines,
divide by 2 = 7860 samples/sec), I could imagine doing a simple game
with sampled audio using a 2LK and LOTS of ROM banks for sound samples.

...time passes...

Ugh, I just tried converting a song to 4-bit samples. Either I'm doing
the conversion wrong, or 4-bit samples sound like everything's going
through a distortion pedal.

What I did was convert a song to 8-bit unsigned samples, then write
a little C program that strips off the bottom 4 bits of each sample
(PC sound cards don't support 4-bit samples natively, so I'm trying to
simulate them that way). The 8-bit version sounds OK, and my stripped
version sounds like utter crap.

I know next to nothing about digital audio sampling... is there a smarter
way to convert than just removing the bottom 4 bits?

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