Audio Cleanup - Noise Reduction

Special Interest Groups Audio Processing
1

Hi,

Just after any advice anybody has.

I’ve been experimenting with Noise Reduction on a 15 second audio clip. I’m trying to extract a voice in the background of a webcam recording, but amplifying the audio results in a lot of noise.

After playing with each of the settings, I’m trying to understand the following:

  1. If your audio input is low volume (background audio), when you amplify it the noise is much more noticeable. Should you perform noise reduction before amplifying the audio, or after? Does the noise reduction tool detect the noise better if the waveform is amplified?

  2. Is it better to try and get the result you’re after from one use of noise reduction? Or should you perform a low dB noise reduction across the clip, then amplify what’s left, and do the noise reduction again?

  3. I like the Residue setting for checking if anything important is removed. What I tend to notice is that in the Residue output, wherever the target sound is you get this kind of “dimmed” effect on the noise. I assume this is a healthy indication that I am not impacting the target sound?

  4. Why would you have a reduced Sensitivity value? As far as I can tell, maxed Sensitivity with a Frequency Smoothing of 1 should always be the ideal setting?

  5. Are there any tutorials or examples with images of the effects that these settings have on the waveform? I find it easier to visualise the result than read it.

  6. Would you ever use Frequency Smoothing at zero?

  7. Quite often the Noise Reduction will reduce the volume of the actual audio to be captured, and a straight forward amplify tends not to fully amplify the whole waveform because somewhere in the waveform part of the wave would be clipped if it amplified the audio any further. I’ve yet to play with the Compressor options but is there a recommended approach to restoring volume after noise reduction has reduced it?

Regards,
Rob.

2

Noise reduction works best when you have a constant low-level background noise… It works best when you don’t really need it. If the noise is bad, “The cure can be worse than the disease.”

…Pros still record in soundproof studios with good equipment and good-close microphone placement, etc… On-location movie dialog is re-recorded in the studio. Even with the latest professional software there is only so-much you can do .

There are no simple answers or simple presets. Generally, you just have to experiment and often you have to compromise and sometimes it’s better to do nothing.

when you amplify it the noise is much more noticeable.

True, but it’s no different from turning-up or turning-down the volume control. (It doesn’t change the signal-to-noise ratio).

Should you perform noise reduction before amplifying the audio, or after?

It’s a good idea to amplify/normalize first It’s usually a good idea to amplify/normalize again as the last step after all other processing/editing.

  1. Quite often the Noise Reduction will reduce the volume of the actual audio to be captured

If that’s happening, I guess your noise is very bad…

and a straight forward amplify tends not to fully amplify the whole waveform because somewhere in the waveform part of the wave would be clipped if it amplified the audio any further. I’ve yet to play with the Compressor options but is there a recommended approach to restoring volume after noise reduction has reduced it?

The “best” solution is to “manually” fade-up and fade-down the volume with the [u]Envelope Tool[/u] because you have complete control, but that’s tedious.

Compression can help but there are several settings to “play with” and it’s easy to mess-up the sound. The [u]Limiter[/u] is a kind of fast-compression and it’s a little easier to use and possibly more effective than regular compression.

You can also try the [u]Leveller effect[/u]. (It’s classified as a “distortion effect” but it doesn’t necessarily sound like distortion.)

3

There’s a fuzzy rule of thumb that if you can’t understand words before cleaning up, you won’t be able to understand them after, either.

Also beware of Audio Pareidolia, where three different people listen to a noisy voice and hear three different things.

I think you just experienced one of the reasons Audacity doesn’t make a very good surveillance recorder.

Koz

4

It’s a good idea to amplify/normalize first

Cool, I wasn’t certain.

The “best” solution is to “manually” fade-up and fade-down the volume with the Envelope Tool

Wow, hadn’t even known this existed! This helped massively once I actually got my head around it.

Thanks for the responses, my end result was more usable than what I started with.

Regards,
Rob.