Audacity Forum

I'm trying to remove hiss & low level background noise from a mic track to which I've applied a profile. After I run Noise Removal, the gain profile is at max throughout the window that was selected for the operation. Am I doing something wrong?

You're not doing anything wrong. Without knowing details of the internals, it appears that effects replace the selection with the affected audio, thus removing the envelope.

AFAIK, the envelope is applied during playback and mixdown. The audio sent to the effect does not have the audio applied.

Applying the envelope before doing Noise Removal is probably not a good idea anyway, as the noise level will vary with the envelope level.

If you want to retain the envelope, select the track and do Tracks > Mix and Render. This will create a new track with the envelope permanently applied.

-- Bill

Very useful info, Bill! It would make quite a difference to e.g., reverb if the envelope is ignored in the signal passed to the effect.

DickN wrote:It would make quite a difference to e.g., reverb if the envelope is ignored in the signal passed to the effect.

True.
The way that I think of it is that the volume "Envelope" is like a "Layer" on top of the sound.
Any processing that you do to the sound occurs in the "sound layer". The "envelope" then adjusts the volume of whatever is playing in the "sound layer".

The slightly unfortunate limitation is that some effects do not just alter the "sound layer", they replace the entire track contents, which means that Envelope Control Points are destroyed. Effects that are known to do this include "Noise Removal" and "Sliding Time Scale/Pitch Shift".
This could perhaps be considered to be a bug - I'll raise the issue with the Audacity QA people and see what they think.

The workaround is to Render the track so that the envelope is physically applied to the waveform. If you want to maintain the ability to "Undo", the best option is probably to make a duplicate of the track before rendering the track envelope, then mute the track and collapse (minimize) it. It's not a perfect workaround, but better than nothing.

Noise Removal should be done before applying any effects that alter the dynamics - so before applying envelopes, dynamic compression, or similar effects. The Noise Removal effect works best on constant noise, so you don't want to make the sound (and noise) level go up and down before you have applied the Noise Removal.

Thanks for the report DickN, it will be looked into.



Gale