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Microphone Month 3

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Hiss Removal = Distorted Audio


I tried the hiss removal tool in Cool Edit pro to remove the hiss noise from some mp3s that I received. However, there is not a ugly distorted noise that sounds as if the audio was coming out of a long water pipe. The frequencies are just too much compressed. What is the best way to do hiss removal with minimum effect on other frequencies ?
February 8, 2007 @07:06pm

Some mp3s cannot be distinguished from their original uncompressed source (by listening) and some are very degraded relative to the original. It depends on the encoder, the particular processing parameters, and the amount of compression. One of the unavoidable characteristics of mp3 encoding is the addition of some broadband noise, which can be quite audible near the low quality end of the scale. This preliminary information is just to let you know that you might be facing a losing battle with decoding, changing, then re-encoding mp3s ... depending.
Noise Reduction is more effective and less destructive for removing hiss than is Hiss Reduction. I have written some extensive instructions on properly using CoolEdit's NR in earlier threads. See if a search can bring up something useful.
February 8, 2007 @09:24pm

You may be applying the processing to heavily. Noise removal is a compromise remember; if you try to completely eliminate the noise you may end up with more problems than you had to begin with.
Also, try finding the dominating frequency of the noise and use a high Q cut. Don't know if it'll work on the type of noise you have, but it may?
February 9, 2007 @02:02pm

I'm sure AndyH's previous posts have mentioned this, but you'd do better to use just the generic Noise Reduction effect, instead of Hiss Removal. I would zoom in as tightly as you can on just the noise you want to remove (find a quiet spot of the MP3, the very beginning or very end--that has this noise in it). Highlight a small sample of the noise (usually 112 milliseconds is the smallest sample that the NR effect will take), then you can pop open the NR window, and 'get noise profile.' Save the profile--then close the NR window (DO NOT HIT CANCEL, hit CLOSE), and zoom all the way out on your MP3, then make sure all of it is highlighted, pop open the NR window again, and make sure your 'noise profile' is loaded, and then let'er rip. You can play with the percentage slider to get a better end result. These guys are right though, NR removes noise from the whole recording, which means it's eliminating unwanted AND wanted frequencies to get at the noise. You have to compromise somewhere.
February 9, 2007 @04:00pm

'ya also gotta remember that 80% of the original information has been removed by the MP3 process to reduce the file size. It's like throwing out 8 out of every 10 pages of a book and then complaining that the story jumps around a bit.
......your just not gonna have pristine audio after that.....
February 9, 2007 @09:03pm

Just to reinforce my first post here, there is a BIG difference in results between uning NR and properly using NR, The basic program help instructions don't cut it.
February 9, 2007 @09:11pm

That is totally correct.
When I use Audition noise reduction, I find it helps to do two things. First, I sample the noise, then zoom in as close as I can to see the noisy waveform. I then do a combination of listening and watching while I apply different amounts of noise reduction.
Since a certain amount of noise is well below audible range, I don't always attempt to remove all the noise since as stated here, that also can remove some of the musical content.
Low level hiss may be masked by the program content and doesn't need to be totally removed if the removal has an adverse effect on the music itself.
Eyes and ears.
February 11, 2007 @07:11pm