ADPCM

[Christuserloeser]

So, Dreamcast's AICA supports hardware ADPCM. - Are there free codecs available that actually use this feature ?

I thought Beats of Rage did, but appearently it's a software codec.


Edit - Interesting post by BlueCrab:

viewtopic.php?p=1004962#p1004962

ADPCM files are just .wav files that have been encoded a different way, and KOS' built-in sound functions can play them (see the sfxmgr.h file in KOS for how to use them).

- Could this codec be used to stream BGM too ?

[Ex-Cyber]

I don't know about the KOS/Dreamcast side of things, but in general it can be used for music. It's lossy, but if the bitrate is high enough it's pretty listenable anyway. Lots of console games use ADPCM for music.

[Guaripolo]

there's a wav2adpcm utility in kos (directory "utils"), i haven't tested enough, but seems to work. It converts a 16 bits RIFF wave to the specific Yamaha ADPCM that Dreamcast uses.

[BlueCrab]

Edit - Interesting post by BlueCrab:

viewtopic.php?p=1004962#p1004962

ADPCM files are just .wav files that have been encoded a different way, and KOS' built-in sound functions can play them (see the sfxmgr.h file in KOS for how to use them).

- Could this codec be used to stream BGM too ?

You could use the built-in ADPCM support for Background music, but in general something more suitable to background music, like Ogg Vorbis will take up a lot less space. Also, the support in KOS for ADPCM files is more based around doing one-off things, like sound effects, but it could be hacked up to doing full background music if one really wanted to (but as I said, you'd be much better off using Ogg Vorbis for background music anyway).

[BlackAura]

If space is a bigger concern that CPU time, something like MP3 or Ogg Vorbis is better. If CPU time is a bigger concern than space, you might has well just use CD-quality .WAV files and stream those - at least they'll sound better.

There is an ADPCM encoder in KOS. It works reasonably well (nxDoom used it to cram all of Doom's sound effects into the 2MB of available SRAM), but I'm not entirely convinced that it's correct - the sounds it generates sound noticeably poorer on a Dreamcast than they do with the included software decoder.

[OneThirty8]

I would go with Ogg like the others said, but if you want to use ADPCM for background music, you could just make a modified version of kos/kernel/arch/dreamcast/sound/snd_stream.c to do the job. It wouldn't be hard at all--the biggest things to change would be in:

Code: Select all

int snd_stream_poll(snd_stream_hnd_t hnd)

The number of bytes it looks for is wrong if you're using ADPCM. Other than that, as long as the sound hardware knows the correct format, you should be able to just feed samples to the sound hardware and have it play.

In response to BlackAura's comment on whether the ADPCM wav files generated by wav2adpcm are totally correct... is this the same ADPCM format as ADX audio? If so, the code that does the conversion in bero's wav2adx/adx2wav is similar but different.

[BlackAura]

In response to BlackAura's comment on whether the ADPCM wav files generated by wav2adpcm are totally correct... is this the same ADPCM format as ADX audio? If so, the code that does the conversion in bero's wav2adx/adx2wav is similar but different.

I've no idea. If you run it through a round-trip (encode, then decode), the result sounds fine, but the encoded file doesn't sound quite right on a Dreamcast.