Hiss after amplifying

Using a Macbook Pro running Yosemite 10.10.3
Audacity 2.1.0 that was installed from the DMG
I’m editing a 2 hour music choral group recording that was done with one mic in the center of the fairly large room. The performance recording is adequate but the conductor spoke very softly, which is reflected in the recording. Recording is a WAV file and in one stereo track.
My problem is when I amplify the conductor’s voice enough to hear I get a hiss in the background. Audacity is set up to NOT CLIP when amplifying and to amplify to the max it indicates 38.8 db amplification. If I amplify to 19.4 (1/2 of max) I don’t get a hiss. Seems like there is some point where the hiss shows up but I’m not sure where that is exactly and I would like to amplify to 34.4 to make this work.

Anyone know about this?

Thanks in advance,

34 dB of amplification is a lot.
If you want to record the conductor and hear him clearly without hiss, you will need to put a microphone near to him - perhaps a lapel mic - enable it when he is talking and turn it off when he isn’t, or if you have a multi-channel recording set-up, record him on a separate channel. You can’t expect to be able to amplify by over 30 dB and have a hiss-free recording.

If you need to salvage the best that you can get from your existing recording, try amplifying first, then apply the Noise Reduction effect. Don’t expect to be able to completely remove the hiss. You may be able to reduce the hiss to an acceptable level. http://manual.audacityteam.org/o/man/noise_reduction.html

Thanks, Steve. Since I’ve come in after the recording was done I can’t change that.
Do you think I can amplify to 30 dB without hiss or is that a calculated guess. It would be nice to know where the hiss comes in without running a bunch of tests.
As always, thanks for the help.


The hiss is almost certainly already in the recording, but at a low enough level to not be noticeable. As you amplify the voice, the background hiss is amplified by the same amount and becomes increasing noticeable. All audio equipment produces some amount of hiss. One of the recording engineers tasks is to keep the amount of hiss as low as possible, and to do that you need to record the signal as loud as possible without clipping. Ideally you would be aiming to record with a peak level of around -6 dB so that only a minimal amount of amplification is required in post-production.