Reduce low volume to silence

I’ve used noise reduction on a book reading to get rid of hiss, and the spoken parts sound fine. But the parts in between, that were hiss, now have a weird warbling; though very low volume.
So I’d like to just make all those parts silent.
Is there a way to do that --i.e. select all sections below a given volume and make them really silent?

Please tell us your version of Audacity and Windows (see the pink panel at the top of the page).

Have you tried increasing Sensitivity to stop the warbling?

You can use Noise Gate to silence the parts in-between your words, but that may not sound very natural. To counter that you could record room noise only and then mix that room noise into the recording.

To install Noise Gate, see http://wiki.audacityteam.org/wiki/Download_Nyquist_Plug-ins#install.


Gale

Win XP, Audacity 2.12

Have you tried increasing Sensitivity to stop the warbling?

I had thought decreasing sensitivity would do that, by reducing the amount removed?
The parameters for Noise Reduction aren’t explained at all really in the wiki. Missing features - Audacity Support
What does “sensitivity” refer to?

You can use > Noise Gate > to silence the parts in-between your words, but that may not sound very natural. To counter that you could record room noise only and then mix that room noise into the recording.

Yes thanks, that seems to be what I wanted.

If 2.12 is not a typo, please obtain 2.1.2 from Audacity ® | Download for Windows.

See Noise Reduction - Audacity Manual.


Gale

If you think of the “gaps” between words and sentences as being the “noise floor”, then as sounds from spoken words trail to silence, the vocal sounds will sink below the noise floor.

The “Sensitivity” control is where the Noise reduction effects sets its “threshold” to determine what is noise and what is sound, relative to the level of the Noise Profile. In most cases, best results are achieved by leaving this at the default setting of “6”.

Setting the Sensitivity a little lower tells the effect to ignore some of the noise, whereas setting it higher tells the effect to assume that the noise is actually a bit higher than the Noise Profile suggests. If the noise floor is not constant through the recording, then increasing the “Sensitivity” can help because it tells the effect to allow for the noise going a bit higher than expected. The down side is that if the Sensitivity is set too high, then the effect is more likely to remove low level sounds that you want to keep.