Before you do anything else on this site, you should read TheUsualDisclaimer.

* No sound at all? You should fix that first! Read about NoSound.

* Noise in a consumer-grade soundcard (soundblaster, etc.)?
  This can often be improved. Read about CheapNoise.

* ACHum is a very common problem in any kind of studio.

* You should definitely learn some PrinciplesOfAudio.
  These don't have anything to do with Linux directly, but
  you'll find that the same issues come up again and again in     every studio.

* ReliableLinuxAudio ... everything having to do with avoiding glitches, dropouts, latency problems... a big section.

* What soundcard should you get? LinuxSoundcards is the section to read. A good professional-quality soundcard can be a big improvement.

* It may be worth TestingYourSoundcard to see what it's
really capable of.

* Reading and Writing AudioCDs on Linux

* Tips for working with AudioFiles ... conversion, clean-up...

* All about DigitalAudio (ADAT, S/PDIF, iec958, toslink, etc)