Expert: Rob Evans - 9/5/2005

Question
Mr. Evans:

I've been ripping audio from cassette tapes and LP's through my Line-In on my sound card. I have used Audacity to adjust speed, Normalize, remove DC offset, edit the amplitude and equalization. What I've done on most cassettes is to fade-out to silence and generate silence between the tracks. I've found that using the noise-removal tool to attempt elimination of hiss and hum creates a "digital" noise in the background -- not acceptable. I've tried using SoundPad to remove background noise. The trouble is that the hiss/hum is occasionally louder than the music on some Classical cassettes, thus in removing the background I lose some foreground. I am not very familiar with the different filters available in Audacity, but I've tried some with limited success. Running it through a low-pass filter to eliminate hiss, then through a high-pass filter to eliminate the low hum results in a "wimpy" sound in the middle. I tried the hard-limiter, whatever that does. I set my wet-level very low and that seemed to get rid of some noise, but got rid of some volume. When amped, some of the noise comes back. I don't really know what I'm doing, but would love to learn. If I get some help from you with cassettes, I'll write you again concerning the LP's!
Thanks!
Matthew

Answer
This is difficult as because, as you say, the frequencies in the music are also found in the noise you want to remove. Firstly, in order to clean up hiss and hum in spaces where there is no music, you need to edit the wave for it's self and remove those areas. The only way to attack the hum and his is to firstly put the track through a graphic equaliser. If you run recording software such as Cubase and Sonar 3, there are VST plug-ins available up to 50 band. This will allow you to take control of the individual frequencies more effectively. You then need to grab the frequencies that are predominant in the sounds you want to remove and reduce them. You will only be able to go so far before it affects the overall sound dramatically. Once, you have removed the sounds that you don’t want. Re-record the track and then enhance that track to bring up the bass and treble again. If you’ve removed the correct frequencies, you should be able to put back some of the umph you have lost.
Hope this helps
Rob