Saskrotch
Offline
Chicago IL

so this started off as me trying to split up some of the tracks in one of the mega man zero games so i could get a better idea of whats going on in each channel. I knew there were 6 channels, because of the m4g demos, but i was surprised when i opened up the channel list in AudioOverload, which is as follows:

GSF DirectSound Left
GSF DirectSound Right
GSF Gameboy Channel 1
GSF Gameboy Channel 2
GSF Gameboy Channel 3
GSF Gameboy Channel 4

So, i'm guessing those 4 channels are from the original GB, to work with the backwards compatibility options. I thought games might use those in addition to the "DirectSound" channels. But in soloing out channels to isolate tracks, i found that the entire soundtrack is coming through the DirectSound Left channel. Basically at the end of this i have no idea about what's going on with the GBA soundchip. So here's some questions i've got:

Is the GBA basically playing back a super lossy audio format?
does the minigsf format bounce tracks down? (the ones i've got are minigsf, i dunno what the difference in formats is)
do some games use all 6 channels, or were the 4 gameboy channels ONLY for playing GB carts in the GBA?

i'm sure i'll edit this as soon as i think of new questions

Beware
Offline

From what I gather, the GBA doesn't have real channels like a regular APU.  All the sounds are created via software other than the 4 GB/C channels instead of the sounds being explicitly restricted by the APU.  The reason there are 2 other channels are for stereo sound.  Most of your GSFs are mono with no use of the GB/C channels as that's what most GBA games were in general.

The Z80 does all the audio work for GBA and GB/C audio.  I also believe that any "channel" limit is strictly the result of the Z80s power, so anything other than the normal GB/C 4 are all lumped together into L and R.  More channels could be possible, but it would result in a significant hit to quality and   require far more effort to program than most are willing to do.

Of course, I could be WAY off base, but that is what I have inferred from your observations, my knowledge of the hardware and my experience with writing GBA music.

ne7
Offline
UK

On the gba, depending on the replay used, when you were creating game audio you could use both sample playback -as well as- the original 4 mgb gameboy audio channels for your audio  ingame...

sometimes you would use the mgb chans for sound effects for example but certain games did use the original gameboy channels as well as sample playback for full music which was rather impressive...

hope that helps :-)

Subway Sonicbeat
Offline
Brazil

I had the same question! This actually helps to understand it.