We have SFX boards in both 2MB and 16MB versions. You may be thinking "Wow, that is nothing, I send emails bigger than that on a daily basis!" But you'd be surprised! For sound effects and small embedded audio devices, you need a surprisingly small amount of space.
Depending on whether or not you compress the audio, have stereo or mono, CD quality or 'every day' quality, you can store anywhere up to approx an hour of compressed music (mono 22KHz Ogg Vorbis on the 16MB version)
First up, remember you can always have compressed audio which saves you a ton of space. The Sound Board can handle Ogg Vorbis (a sort of royalty-free MP3 format) in any bit rate
Most projects do not need true stereo, if you are only using one speaker or if you don't need two distinct channels, record/convert your audio as Mono! You'll get the same audio from both left and right channels and fit 2x as much music.
CD quality audio is 44.1KHz 16Bit, thats 44100 2-byte samples per second. While you can decode audio on the Sound Boards at that rate, often times your speakers or headphones aren't that good anyways.
We suggest sticking with 16 bits, but reducing the sample rate to 22KHz unless you are piping the audio into a quality stereo system or expect users to have fancy headphones plugged in. If you're doing 'voice' type effects, you may be able to go down to 11KHz. Every time you reduce the sample rate, you can double or triple the length of audio.
The absolute biggest files you can generate and play are CD quality uncompressed stereo WAV files, at 44.KHz/16 bit.
Stereo WAV 44.1 KHz 16 Bit - (2 bytes * 2 channels * 44100) = ~175 KB per second, so 2MB can hold 12 seconds, 16MB can hold 90 seconds
Mono WAV 44.1 KHz 16 Bit - (2 bytes * 1 channels * 44100) = ~88 KB per second, so 2MB can hold 23 seconds, 16MB can hold 180 seconds (3 minutes)
Stereo WAV 22 KHz 16 Bit - (2 bytes * 2 channels * 22050) = ~88 KB per second, so 2MB can hold 23 seconds, 16MB can hold 180 seconds (3 minutes)
Mono WAV 22 KHz 16 Bit - (2 bytes * 1 channels * 22050) = ~44 KB per second, so 2MB can hold 45 seconds, 16MB can hold 6 minutes
Stereo WAV 11 KHz 16 Bit - (2 bytes * 2 channels * 11025) = ~44 KB per second, so 2MB can hold 45 seconds, 16MB can hold 6 minutes
Mono WAV 11 KHz 16 Bit - (2 bytes * 1 channels * 11025) = ~22 KB per second, so 2MB can hold 90 seconds, 16MB can hold 12 minutes
You can compress or convert any kind of file (like MP3) to Ogg Vorbis and its royalty free!
Since it's compressed, Ogg Vorbis does lose a little quality but its very unlikely that you will notice. The only real tradeoff for Ogg files is that the Codec is a little slower so it takes longer to play files, on the order of 50 milliseconds or so. In general this is not noticable, but if you are looping audio with a TnnHOLDL.ogg file, you'll notice a small gap.
Ogg Vorbis is about 1:5 to 1:10 compression over WAV files, so you can store 5-10x as long audio if you compress it to Ogg, compared to the numbers above