I do not normally post on these boards but as a computer scientist and audio engineer by trade and a pilot by choice I think I may also be able to help.
Assuming you're actually looking for higher quality audio, recording transmissions at a higher bit rate will not increase the quality. As has been stated, the real quality issues show up when the data (ATC audio in this case) is being transmitted via analog radio waves through a noisy medium (the air). Attaching a high quality medium on one end will not change or increase the quality. It would be like attaching a fire hose to your kitchen sink. Pretty pointless.
The only "real" way to get high quality transmissions is cut out the low quality medium. For example: You could fork a pilot's headset as well as a controller's headset directly into two recorders and splice the files together later. Or, for even better quality, you could get a real pilot and a real controller into a studio and record them there.
Even if you had the means to accomplish this, what would all this trouble really give you? Thanks to movies and television most everyone knows what radio transmissions are "supposed" to sound like. High quality radio chatter would sound exactly like what it would be. Fake.
On the other hand, If you're simply looking to change the bit rate to make it compatible with whatever application you're working on this is easy. Find a freeware audio converter and switch the bitrate of one of the files you find on this site.
Finally, I can tell you that the audio you find in the archives on this site is of comparable quality to the audio I hear over my headset when cruising the skies.
If there is anything I can do to help you, feel free to leave me a PM. For example, if you want some audio as if you were in the plane (high quality pilot, low quality ATC) I'm willing plug in a recorder to the copilot headset jack on one of my flights.
Best of luck!
- Wolf
