cleaning up audio signals

[fibbingbear]

Given how much effort goes into cleaning up video signals, I noticed that I could not find nearly as much information on doom9 about audio signal cleaning (which is very important for the overall presentation of a video). Crawling the forums yielded some info on low-pass filters (which don't seem to be very effective) and a CoolEdit filter.

Given that there's such a variety of ways to clean up video, how come such a dearth for audio? Do people feel that ogg/mp3/aac/whatever do a good enough job of cleaning the signal while encoding?

[Southstorm]

Are you working on a specific audio project?
There are many ways to manipulate audio, i.e. highs, lows, mids, equalizing, pop & hiss removal, normalization, etc...
As far as the audio compression you mentioned, ogg/mp3/aac and so forth, these only compress the audio, they do no "cleaning" of any sort.
Myself, when I need to "clean" up some audio, it gets converted to a WAV file, uncompressed, then I put on my best pair of headphones and go to work.
So what kind of cleaning are you looking for?

[Yobbo]

Adobe Audition has an exceptionally good Noise Reduction facility. I myself would be interested if anyone can suggest anything better?

It seems some folk are pleased with how Audacity's noise reduction has progressed (latest version), but I've yet to try it. I always go straight to Audition for that sort of work!

[GrofLuigi]

I gave up on noise reduction filters - they either sound like tin can or don't clean enough.

Lately i touch VHS captures with audition's spectrum representation - there is always a horizontal line near 8-12 kHz (don't know if that's characteristic of VHS in general or just my VHS recorder - but looks right for VHS). I cut just below it (if the majority of the sound doesn't reach up to there), normalize and have clear conscience that I've done all I could with the sound without destroying it.

If you don't have audition it's probably hard to visualize, but it's simple enough - cut high frequencies that are mostly noise on VHS anyway. Like lowpass filter but with picture. :)

GL

[fibbingbear]

Thanks to everyone with the information!

To answer Southstorm's question: I capture sound/video off of my consoles and through my graphics card and sound card. The signal is fairly clean. On places of silence, there are some very minor fluctuations, which I presume is noise. So the type of cleaning I want to remove is light random noise. I care about capturing the signal, but not capturing the noise :-)

Also, to respond to Southstorm's comment that AAC/MP3/etc don't clean the sound, that's true, but sometimes saving at lower bitrates can mask out imperfections in the audio. I was wondering if saving the sound at a lower bitrate (like 128kbps OGG or AAC) could do some of the cleaning for me.

Out of curiosity, to clean light noise, couldn't one Fourier transform the signal, and then just remove all the frequencies that have small magnitudes?

[Southstorm]

With a frequency analyizer combined with a graphic EQ, you can locate the "noise" frequency, then eliminate it with little or no difference in sound.
Though you can "mask" out some imperfections by lowering the bitrate, essentially, you're removing detail. There's certainly a "sweet spot" between having too high bitrate that wastes space, and too low a bitrate that introduces sound artifacts.

[guada2]

I myself would be interested if anyone can suggest anything better?

Have you tested this:
IZotope RX Complete Audio Restoration v1.04

Knows that other solutions (softwares) exist.

Bye.