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Hehe :]
Thanks!

Hi

The nesdev wiki is the definitive reference on this: http://wiki.nesdev.com/w/index.php/APU_DMC. It's also extremely technical, so I'll try to sum everything up.

If you know how regular PCM works, let's start from there. Imagine you've got a 7-bit PCM channel. Now, instead of being able to change to any other value each sample, the DPCM channel can only increase or decrease by one from the previous value (so it also acts as something reminiscent of a typical lowpass filter). That also means that if your sample contains silent parts, these are actually converted to a sequence of +1 / -1 / +1 / -1.
A picture can probably do way more to illustrate the difference (top: PCM, bottom: in DPCM)

(I've used a snare sample)

In theory, you can use bankswitching and just continually stream new sample data (you can verify that in FamiTracker btw). In practice, ROM chips were not free, so games usually had a few one-shot samples and since they didn't want to bankswitch during playback either, these had to fit in a specific memory range, $C000 - $FFF9, just about 16kB. At the standard rate (33143.9 Hz), that gave you about 2 seconds.
So to answer your question - there are no theoretical limitations, but if you'd like to maintain the feel of actual old game soundtracks, you'd use short samples.

The DPCM channel has a rudimentary way of playing the sample back at different rates that approximate some musical notes. I believe sunsoft bass used exactly that technique. I'd suggest you look at the pitch table in the nesdev document I've linked, especially at the note column, to see how dirty that actually was :].
Nowadays, it's also common to just have different samples for different notes and play them all at the maximum frequency. It all depends on what you're trying to achieve.

I'd say just load the samples to FamiTracker, have them all played once, export that to WAV and then load the results into chipsounds. It's a bit of extra work, but worth it if you'd like to sound authentic.

EDIT: Oh, and just a small clarification, it's actually the 2A03 chip (that's the NES CPU with integrated sound circuitry) that has the sample channel.

Hello and welcome!

I actually really like Midnight Brawl! Good job on that & more tracks like it, please! :]
Child's Lullaby is that kind of game cutscene music I'm not really a big fan of, but hey' that's me. Could maybe use some polishing - some more variance in instruments / melody?

Also if you could, .nsf downloads would be appreciated!

Hi,
what are you writing your tracks in? FamiTracker?

(all of these steps also have a "B" option - ask someone nicely to do them :])

I'm assuming you have a final selection of tracks at this point and are just looking to put them on a cart.

1. Determine what mapper to use. Basically your cart is gonna have a ROM chip with the music data + replayer, but depending on how complex your album will be (# of songs, do you use a lot of different samples, etc...), things can be very simple or very complicated (on the simple end you'll get along with the simplest SMB1-like cart with two ROM chips, on the complex you'll need banking, worse yet, you might have to bank the track itself during playback, if you rely heavily on samples). Nesdev wiki is an absolutely necessary reference (for me at least, I forget / look stuff up again all the time)! Here's their page on mappers. For all other steps, nesdev will be your friend too, they even have a forum if you need to ask some technical question.

2. Prepare a .nes file that works in one of those "as exact as possible" emulators. If you're doing this by yourself, you'll probably have a basic knowledge how to translate that into actual hardware at the end.

This is the step where all the acutal programming goes on and is very dependent on the software you're using to make your music. It's also complicated and would require a longer description than one forum post. If you're new to this, here you'll either have to do a lot of learning or ask someone for help. Basically with famitracker, you get the replayer source and you can also export the raw data it understands. Then you need to write some song selection interface and spend lots of time frustrated because @##$% won't work still.

The .nes file actually describes what a real world cartridge contains, so in most cases, it's a 1:1 .nes -> hardware process afterwards.

(optional but very recommended: test with a cart like PowerPak, just to confirm your project actually works on a NES before writing 50 carts and finding out they don't work. Also remember to later test the first actual cart you make!)

3. You could find a matching game to sacrifice, but I'd say don't ruin old cartridges and buy new carts instead.
Last time I wanted to do stuff like this, retrousb used to sell new cart boards and cases, for some reason I don't see these on their website, but apparently infinite nes lives does that now. I don't have actual experience with them, but I see no reason not to try their stuff!

Apparently they even provide a ROM chip programmer, so that sort of saves me the trouble of writing step 4, that would be "get a ROM writer, blank programmable ROM chips, program them, solder everything".

Also note that the selection of available boards further reduces your mapper options!

After that, you're done.

I don't know how experienced you are with any of these steps, or if I didn't explain something clearly, so feel free to ask more in-depth stuff about anything. This is just a basic outline of what to expect and how I'd do a project like this.

Good luck with your project!

A good place to start is checking out all the FamiCompo archives! :]

Oh and definitely check out Rushjet1, I'm currently listening to his Mega Man remakes and they're awesome!

Other than that there's too many to list.

EDIT: Added some awesome tracks:

No problem!
Cool, didn't know about this site. The note about voltages reminds me though - the rated voltage must be the same or bigger. Don't replace with smaller values, unless you're sure. They probably only warn you because they send some with bigger voltage rating (and that is OK).

If you by any chance run into a situation where the original caps are rated higher, it's better to double check with the schematic or ask someone to check for you. Generally, most of the C64's internals run on 5 V or 12 V, but the internal power circuit could require bigger values.