SuperNSF NSFs do tend to work on a PowerPak, though you can't change tracks or quit because it hogs the CPU.
The limit I think is actually 252k. I think 4k is reserved for the NSF wrapper (haven't checked on this, but every time I've tried a 256k NSF it's crashed).
SuperNSFs work on the HFC3, but it's super buggy. The NSF will restart randomly, and sometimes hang in random locations for no apparent reason. I've only successfully played Heim This! once so far...
Of course that's an issue with the HFC3, not the NSFs themselves.
Tried them out on my PowerPak, and only 2 of these seem to work (but if even one did, then they all do). The only problem seems to be the files being too large for the powerpak to load them properly. After reading the nesdev thread and trying to comprehend what's being said, these NSFs are using only the 7-bit PCM mode, and as such should also work on an unmodified NES, though I haven't tried these on my stock one yet.
EDIT: Oh, look there's an automatic reset.
AGAINEDIT: That's probably caused by the fact that I use batteries to power tat NES. Also, I'm uploading a video of this to youtube for those unfortunate enough to not experience this audible glory...
Yeah they are mixing 4 virtual channels in software.
I'm not sure about the bit-depth. Apparently the more "channels" you use the lower the bit-depth goes to stay within the 7-bit limit of $4011
I don't get why this couldn't have any practical uses though...in a simple puzzle game or a visual novel or something that doesn't have too much going on this would be quite usable, imagine 3-4 30-40 second PCM loops as the soundtrack for the game. Even if the text would lag it would be fine as long as the music doesn't get interrupted.
There are several Atari ST games that have MOD music played via similar PCM means on a static title screen, and then regular PSG stuff during gameplay. I guess Action 52 is in this category as well.
The main problem with it is PCM data eats up ROM space very, very quickly. A 40 second PCM loop at 8kHz requires ~320kb (most large NES games have 256kb PRG data total). Even if it's MOD style samples like with SuperNSF, it's still very space intensive.
I did some reverse engineering of Big Bird's Hide and Speak a while back, and discovered a complex PCM compression scheme, and they even crammed a bunch of PCM sound onto the CHR graphics chip so they could pack in more sound. I think it had the most PCM data of any NES game, and it was a total of 44 seconds of samples compressed down to about 232k of data.
Anyhow, yes of course it's possible, but it doesn't come easily at all unless you want to make some big sacrifices.
There are some really weird mappers made by chinese developers who still make pirated games for the NES, or for clones really, that can handle 2MB PRG rom and stuff like that. Of course developing for something like that would make real cart production very difficult but still, it would be for a better cause, and most of those games only need that amount of space because they are very badly optimized.
