After much thought, I believe I have found a way to record audio through the link port! I'm doing this because I thought it would be a cool project and it might make song creation easier.
How it works:
User inputs the beats per minute for the song(until I find out how to make b.p.m. recognition software)and is saved as a variable that will tell the link port to receive any number of bytes for a specific period of time that's raised or lowered depending on the b.p.m. rate for accuracy.
For example, let's say the b.p.m. is 60 alright and so the link port will stay open and receive bytes for 1 second,store those bytes(as packets or something) it received every 1 second because the number of bytes it received should give us the frequency, and then when the song is done it will stop receiving bytes,have you unplug the jack of course and take each packet of bytes, count how many there are thus giving us our frequency and finally convert that into music note values which can be stored in a blank mt3 song using an on-calc compiler.

note: I actually haven't started programming this yet as the idea for it popped into head THIS morning and I am still researching it.

So feel free to leave any questions,comments and advice as I hope to know what you all think of this!

I don't understand what you're trying to do with the part "the number of bytes it received should give us the frequency". If you're reading audio data from the link port continually, the number of bytes is always going to be the same. The only thing that varies is if you get a 0 or 1 when you read the link port. It would be possible to record those 0s and 1s, but I don't know how fast you can do it, and I can't imagine that a 1-bit recording is going to sound good...

Also, converting audio data to an MT3 song (or another MIDI-like format) is not a trivial task, even on a PC.

By frequency, he means sample rate. For example if you were able to read from the serial port 8000 times during one second your sample rate would be 8000hz.