CGB MP3 players

Discussion of programming and development for the original Game Boy and Game Boy Color.
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pikachu64
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Location: Upstate NY, USA

CGB MP3 players

Post by pikachu64 » Sun Mar 03, 2019 7:27 am

So i've been looking into driving high quality audio with the Gameboy Color. I did some searching and stumbled upon the SongPro™ MP3 player for CGB. I was surprised that such a thing exists as I did not expect CGB to be capable of audio output approaching 44.1kHz * 16-bit * 2. The SongPro is akin to the official Nintendo PLAY-YAN for Gameboy Advance/SP and PLAY-YAN Micro for Game Boy Micro, also known as Nintendo MP3 Player.

Unlike the Play-Yan, the SongPro seems virtually impossible to get a hold of. Here are some articles I found on it:

https://www.ign.com/articles/2001/01/10 ... -the-beats
https://www.retrothing.com/2006/04/songpro_mp3_pla.html (Includes picture)
https://www.myce.com/news/Songpro-makes ... ayer-4095/

Without getting a hold of the cartridge or seeing footage it's impossible to say what its capabilities really are. Does anyone have one or have any thoughts on how it's implemented?

tepples
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Re: CGB MP3 players

Post by tepples » Sun Mar 03, 2019 10:07 am

All the decoding is done on the cartridge.

nocash
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Re: CGB MP3 players

Post by nocash » Sun Mar 03, 2019 12:18 pm

I think so, too. The gameboy hardware is probably mostly used as "power supply" for the mp3 player, and apparently also for button input and screen output. It doesn't look so useful, the main motivation might be that "it is for the gameboy", if that is a priority when buying things.
For the audio, the cartridge slot has an external audio input, but it's mono, and I don't know if GBA is supporting that, too. Anyways, it might work for passing audio to the internal speaker. And I would expect that the cartridge has its own headphone socket for external stereo audio output.

pikachu64
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Joined: Tue Feb 06, 2018 5:32 pm
Location: Upstate NY, USA

Re: CGB MP3 players

Post by pikachu64 » Tue Mar 19, 2019 5:58 pm

Thanks for the replies. I read the following on GB/C sound hardware:

- http://gbdev.gg8.se/wiki/articles/Gameb ... d_hardware
- https://problemkaputt.de/pandocs.htm

Are there any different resources that talk specifically about driving stereo audio (headphone jack output)? I'm interested in seeing what can be produced with the standard 4 (2 x 4?) channels and also Vin, without any microprocessor on-cartridge.

tepples
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Re: CGB MP3 players

Post by tepples » Tue Mar 19, 2019 8:12 pm

By turning on all DACs and bit-banging the volume register, you can achieve 3-bit-per-channel stereo audio output. But you need some way to generate those 3 bits at an acceptable speed on a 2.1 MHz CPU with no multiply. It's not like GBA where you have 16.8 MHz and a fast multiply with which to decompress transform or linear predictive codecs.

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