What's the best way I can do this? I know that NSFs are very small & don't take up much space. Plus, they're 22.05 kHz sampling rate or lower. What should I do to get these to WAVs, bing that each file isn't just one track, but rather a collection of tracks (like SIDs)? NSF is the NES Sound Format.

I'd also like to get some GYMs turned into WAVs (&, in turn MP3s). These are a bit higher quality & are what's used in the SEGA Genesis. Each file is a track. I'd also like to add a 3-second fade-out to any track which loops, as usually only one or two loops is present, and the song ends abruptly.

Thanks...

I don't know about GYM, but there's Foobar2000 plugin for playing NSF files, with diskwriter you can conver them to WAV, then (if needed) with some audio editor (like Audacity) split a collection of tracks to separate tracks, add fade-outs, etc.

I probably should've thought of this. Does Foobar2000 deal with modules? If so, is performance & sound quality better than BASS?

Yes it can play modules, and it uses BASS.

Foobar uses exactly BASS 2.0 dll.

foo_mod uses bass.dll, but the recommended plug for module playback are now foo_dumb. Both can be found at Kode54's page. Plugins for NSF and GYM, SID and others can also be found on this page. Another GYM plugin and more can be found here. And here's a plugin for DMF modules.
There's possibly more foobar2000 "game music" plugs around, but I don't know where...
With foo_diskwriter and foo_clienc you can directly encode your module into any format you've got a console encoder for, without going via wav file, but if you want to edit the wav files before compressing them, just diskwrite to wav.

[EDIT]
And here's a page with more plugins.
Readers of this thread should also look at the parallel thread.
[/EDIT]

I fed mine into winamp with diskwriter set as the output, and you can compress the resulting wavs with whatever you want.

What decoder did you use? The default one?

ymamp for gym, nosefart (!) for nsf

both available from winamp.com with a plugin search

Ah, sorry, I was distracted by adam917's post about modules…
Winamp's default module decoder is obsolete, that's why I asked.

Sorry to revive an old thread, but I'm wondering if anybody can help me with NES sound emulation...

For starters...
1) What, if any, would be the best sampling rate to reproduce the NES sound?
2) At what frequency, if any, should I apply a lowpass filter?

Bumpety bump-bump

I would recommend 44100Hz, and stick with the default lowpass options, unless you want the chip sounds to further murder the quality/bitrate.

For the actual rendering, I recommend either foo_gep or foo_festalon. Or, if you can't use foobar2000, and know how to code your own front-end, I recommend the respective libraries, Game_Music_Emu or Festalon. They are more likely to produce output free of aliasing, which should also improve the encoding over something which synthesized the signal without any supersampling or other band-limiting.

PS. Bumping is bad, mmkay?