Intentional PPU hum...

[Karatorian]

I don't know much about the signal levels on RCA cables, but what would happen if you took a Y cable (I've got one I use to split the mono audio to left and right), and used it to mix the audio out and video out together? Would this be safe? Would the levels be such that you could usefully combine PPU and APU audio output?

Even if that didn't work, you could use a Y cable to send the video out to both the audio and video, so that you can see and hear this hack at the same time. I wonder if it'd be possible add some more interesting content to the video signal without compromising the sound quality too much. If so, it might make for some unusual demos. (Or even games?)

[rainwarrior]

Yes, I used a Y cable to split the video signal to make the video I posted. I wouldn't suggest that this will work in all cases (probably depends a lot on the video and audio inputs you connect to), but it was good enough in my particular case to make that recording. If you were doing it properly you'd want an active splitter that can buffer the two outputs, not just a passive Y cable.

[blargg]

I think the video would overpower the audio if you connected them. For one, it has 68-ohm impedance, while audio has 150 ohms. And the video signal is mostly a full-modulation pulse wave at low frequency, very loud.

[darkhog]

Could you put some custom code into say SMB that would play what is actually on screen instead of standard Mario tunes in similar way this does? Would like to hear how SMB playthrough sounds like.

[rainwarrior]

Why would you need code? Just connect the video out to your audio in and you will hear what's on the screen.

For the most part it's just going to be some kinda 60hz buzz with a timbre that varies as the visuals change. (Maybe I'll try making a video of this to demonstrate once I've got some other stuff finished.)

[lidnariq]

You're basically not going to be able to hear any difference as to where things are on the left or right side of the screen; your ears can't hear at those frequencies. All-in-all, it'll sound like a bunch of overtones of 60.1Hz, at varying strengths, and there will a strong correlation with total screen brightness and loudness.

[rainwarrior]

It ended up sounding even less interesting than I'd expected, and my expectations were low.

[darkhog]

Why would you need code? Just connect the video out to your audio in and you will hear what's on the screen.

For the most part it's just going to be some kinda 60hz buzz with a timbre that varies as the visuals change. (Maybe I'll try making a video of this to demonstrate once I've got some other stuff finished.)

My idea was to add code that interprets pattern/name/attribute table data as sounds and send those into APU instead of playing standard music. Not something silly like connecting video out into speaker.

[rainwarrior]

Oh, well I guess you could do something like that, but this thread is about using the PPU for sound!

[darkhog]

Well, it'll still use PPU for sound, just differently .

[lidnariq]

"Music that has something to do with what you see" has a long standing history in game use, but the specific bit about using the PPU implies using the one thing the PPU can do well: be a 4 bit DAC at 5MHz.

Playing (optionally transformed) level data as sound is about as relevant to the PPU as it is to a beverage one might drink while playing.