Intentional PPU hum...

Discuss NSF files, FamiTracker, MML tools, or anything else related to NES music.

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hap
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Post by hap » Fri Apr 03, 2009 11:43 pm

How about an audio recording of nesdev_anthem.zip B00daW? :)

yay, the same concept on TMS9918 family graphics chip, as you can see, amplitude can be changed by changing brightness.
http://www.youtube.com/watch?v=rGA_fVegAb4
I spent most of the time creating note- and lengthtables. :(

sourcecode here if anyone's interested: http://samor.nl/hap/crap/vdpmusic.zip (the .com is not for PC)

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tokumaru
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Post by tokumaru » Sat Apr 04, 2009 6:47 pm

This is all very nice, but is it also possible to make some video out of audio signals?

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Dwedit
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Post by Dwedit » Sat Apr 04, 2009 7:28 pm

Probably not, seeing as you'd need HBLANK and VBLANK in order to have video frames.
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Post by tokumaru » Sun Apr 05, 2009 4:46 pm

Dwedit wrote:Probably not, seeing as you'd need HBLANK and VBLANK in order to have video frames.
And there's no way to simulate those with audio? I'm just curious, I know nothing about audio and video signals.

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Post by lidnariq » Sun Apr 05, 2009 8:22 pm

tokumaru wrote:And there's no way to simulate those with audio? I'm just curious, I know nothing about audio and video signals.
Sure you could. You just need a ~60/50Hz pulse wave and a ~15723/15625Hz pulse wave. Only problem is that the NES has a maximum pulse wave frequency of 14kHz, which most TVs won't sync to. Depending on the television, you might be able to drive at the first undertone (~8kHz) and have it sync.

Drawing things in addition to generating sync will be nontrivial, however.

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tokumaru
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Post by tokumaru » Sun Apr 05, 2009 8:58 pm

lidnariq wrote:Drawing things in addition to generating sync will be nontrivial, however.
I was just curious as to what kind of things would be possible. The resolution of whatever was generated would probably be laughable.

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Dwedit
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Post by Dwedit » Sun Apr 05, 2009 11:46 pm

You might be able to generate something like a TI83+ can if you're lucky, but a TI83+ has a 6MHz Z80. Is the NES fast enough for generating anything visible through PCM output?
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blargg
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Post by blargg » Mon Apr 06, 2009 1:28 am

lidnariq wrote:
tokumaru wrote:And there's no way to simulate those with audio? I'm just curious, I know nothing about audio and video signals.
Sure you could. You just need a ~60/50Hz pulse wave and a ~15723/15625Hz pulse wave. Only problem is that the NES has a maximum pulse wave frequency of 14kHz, which most TVs won't sync to. Depending on the television, you might be able to drive at the first undertone (~8kHz) and have it sync.
$4011 can be used to generate frequencies of up to ~447 kHz.

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B00daW
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Post by B00daW » Mon Apr 06, 2009 8:25 am

nesdev anthem is a cover of that really annoying mouser.nes song. ;P

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Post by tepples » Mon Apr 06, 2009 11:41 am

B00daW wrote:nesdev anthem is a cover of that really annoying mouser.nes song. ;P
Which in turn is a cover of E2M3.

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Re: Intentional PPU hum...

Post by rainwarrior » Sun May 12, 2013 12:09 pm

Since emulators aren't very good at showing this off, I made a video of nesdev_anthem.nes:

Image
http://www.youtube.com/watch?v=xjrFJbN5iCc

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Re: Intentional PPU hum...

Post by tepples » Sun May 12, 2013 12:59 pm

I think I know how to get more bit depth. Vertical mirroring, black nametable 0, white nametable 1, use $2005 as if it were $4011. What this ends up doing is using the scroll to create pulse width modulation.

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Re: Intentional PPU hum...

Post by blargg » Sun May 12, 2013 4:42 pm

I thought you just outputted the 1-bit waveform to $2007. I take it this approach is to have the PPU hardware output a continuous tone without CPU assistance.

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Re:

Post by zzo38 » Sun May 12, 2013 7:54 pm

hap wrote:On another note, it shouldn't be too hard to add this PPU noise as simulation to emulators...
Yes, if it actually makes the NTSC signals (rather than RGB mode), it will work.

Can you make music through the tape output? Can you make a music combining the video out, 2A03 audio out, mapper audio, and tape?
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B00daW
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Re: Intentional PPU hum...

Post by B00daW » Tue May 14, 2013 8:05 am

When I was experimenting with it, I noticed using other color and brightness values it made louder or softer waveforms. If someone were to experiment, they could create a look-up table of the loudest to softest or softest to loudest to create PCM waveforms.

...It would also be prettier.

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