Noise Reduction / Stereo to Mono / Volume

I am working on a conference recording in order to make a radio broadcast.
The sound was recorded with a Zoom H1 (internal microphone).
The original recording is in stereo. The sound is very low, so there is too much souffle. I must proceed a Noise Reduction.

A few questions:

  • I am wondering if I should change the sound from stereo to mono before proceeding the noise reduction. Or not… What do you think is better? (No need Stereo for Radio)

  • I guess the Noise Reduction must be done before amplifying the sound or changing the envelope. Am I right?

  • What is better in this situation: changing the envelope or using the Amplify effect? (The change must be applied to the whole file).

Doesn’t really matter.

Doesn’t really matter, but it could be confusing to use a non-constant envelope before Noise Reduction.
For low level sound recording, amplifying first has the benefit that it’s easier to hear the effect of Noise Reduction.

For constant amplification, it’s simpler to use the Amplify effect.

The way I would do it is:
Stereo to Mono → Amplify → Noise Reduction

Listen to the track after each step to ensure nothing unexpected occurs.


After many tries and long researches on audacity manuel & wiki, that’s basically what I’m doing now!

To be more precise, this is what I am doing in order:

  • Stereo to Mono
  • Limit (to get rid of some irrelevant peaks, otherwise I cannot Amplifie)
  • Amplify
  • Notch Filters & Low Cut (I’ve noticed the Noise Reduction will be better if I first get rid of some frequencies that are constant in the back noise - I had to learn how to use the spectrum view for this)
  • Noise Reduction
  • Compressor (to get more constant volume - and to amplify again since I’ve lost volume in all the previous steps)

Long work but learning a lot!

As a general rule, it’s better to use Noise Reduction before effects that change the dynamics (such as compressors, expanders and limiters).
The reason for this is that Noise Reduction works best when reducing a constant level of noise. Effects such as compressors and limiters apply a varying amount of amplification / attenuation to the audio, which causes the noise floor to vary, thus reducing the effectiveness of Noise Reduction.

If it is clicks and bumps that prevent amplification, then by all means edit them out (delete those bad bits) before applying Noise Reduction. If it is “normal” high peaks (that you wish to keep), then do Noise Reduction first (before the limiter / amplification).

Yes, that’s what I understood…

But since I needed to Amplifie before working on the Noise Reduction (to hear good…), I made the choice to apply a Limiter before.
It is the default Limiter of Audacity, set up to Hard, and the db level I choosed is only affecting a very few peaks. Then I could Amplify and hear better my Noise sample to make sure that only the constant back sound was taken.

I think it is not the perfect way: I could have amplified only the sound sample, then go back to unamplify it once choosed… But since the result is not bad, well, I keep it.

The constant back sound I have to deal with is a PSSSSHHHHHH produced by the sound system in use during the conference I was recording. I was too closed from it, for sure! (because I was afraid to get too many sounds from the room)
My original sound level is really weak. I managed now to get a quite good result for voices spoken through the microphone.

But since sometimes people were asking questions without speaking in the microphone, it makes it extremely difficult to get an acceptable result for these parts! Really weak voice… very strong back pssshhh… with sometimes another noise from the room covering the voice…

For this, I guess there is no magical way to sort it out…

Next time, I must stay far away from the output of the sound system!
And set up my recorder to a higher recording level…