Subject: Re: [stella] Announcing "webTune2600" From: Doug Dingus <opengeek@xxxxxxxxx> Date: Sat, 13 Aug 2005 17:17:17 -0400 |
On 8/13/05, B. Watson <atari@xxxxxxxxxxxxxx> wrote: > > > > 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? Actually you hear a coupla things. You get the 60Hz note, plus this wierd updownupdownupdownupdown pitch. 60 isn't fast enough to blend, so you hear both rapidly next to one another. (It's a cool effect, but not really musical.) 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). LOL!! If it's all in key, it works! 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...) I don't think that would get it done either. The cycle time varies with pitch. I pasted one cycle of one frequency in with another into an audio editor, then copied that to build up a second or two of audio. Too many timing problems at the 2600 speed. When I wrote cycle, I meant one audio cycle, followed by the other one. CPU cycles just don't match up. 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? The other posts have this exactly right. I would trim the audio a bit farther below the limit however, but that's just me. You should be able to get AM Radio quality sound (a good AM radio that is) out of a 2600 that way. 4 bits can sound fairly good actually. I've a question along these lines. The 2600 has two 4bit audio channels right? Using them both together could get more than 4 bits of sound. What's the maximum audio output without distortion? When they add together, is there room in the rest of the circut to handle both channels? I remember the 8bitters having some limit on the 4 channels. If the sum of the 4 was too high, distortion would result. -- > B. > Archives (includes files) at http://www.biglist.com/lists/stella/archives/ > Unsub & more at http://stella.biglist.com > > Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://stella.biglist.com
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