I am using Digital Performer 7 with Waves Plug-ins to fix up an interview that was recorded over the phone. I know that I won't be able to change the grainy voice, but I was wondering if anyone had any tips to make the sound a little nicer. I can't really subtract noise, because the problem is the voice itself.
Really, the best you can do is get rid of some of the noise. A telephone has a frequency response of 300Hz to 3400Hz (in North America, at least), so most of the frequency ranges you'd be EQing to affect voice tone are not even present in the signal. If you boost above 4kHz, you'll just be boosting line noise, as there was never any audio there to be boosted. I find it quite frustrating to work with phone audio.
What I normally do with such signals is try to eliminate as much noise as possible, first by EQing out the frequency ranges containing only noise, then by passing the result through a full-band noise reducer, like Z-Noise. I have to check myself not to go overboard at this point. Leaving a bit of noise in there smoothes the overall result a bit. The phone signal is already very compressed, so playing around with dynamics is not likely to get you anywhere. A bit of additional EQing will let you address the voice itself at this point, but the scope is very limited.
Basically, you'll be scratching your head, wondering what else you could possibly do to make it better.
I will agree with Jean Christophe, but will add that really anyone who records an interview in such a way really should not be surprised at the audio quality resulting. Dont waste time on it. Youre on a loser really.
You cant make a silk purse out of a sows ear.