Sorry guys, please let me clarify.
Researching how to program GameBoy, I came across software that appears to allow you to take WAV files and convert them for use in a ROM project.
EXAMPLE:
MM_X's GameBoy Wave Convertor - Posted by: Jeff Frohwein
One program allows you to convert raw 8-bit audio files to GB format wave files that can be played on the GB by dynamically updating GB wave RAM memory ($ff30-$ff3f). Two programs are included in this freeware DOS package. RAW soundfile to GameBoy 4-bit (also "packs" nibbles together), GameBoy 4-bit to RAW soundfile ("unpacks" nibbles). It runs fine in a Win95 DOS box.
Source: http://devrs.com/gb/software.php#misc
Here is a link explaining how to install it:
http://cratel.wichita.edu/cratel/ECE238
dioSamples
There's also another program:
Graham's Tool - Posted by: Jeff Frohwein
Here's windows software to convert .wav files to 4-bit GB format & Visual Basic source code. Other info can be found here as well.
Now is there something that these sites are not explaining about the sound files? It sounds like you can take a WAV file and then convert it for use in programming.