Dealing with spoken voices, they sometimes come spoken in telephone, walkie-talkie etc., other times they are clouded by out of breath, anger or other strains. These have in common a high volume of background noise. Can anyone explain me how to turn up background noise volume without turning up spoken volume?
You can try some dynamic compression (Effect → Compressor).
Dynamic compression reduces the dynamic range (or “dynamic contrast”) by reducing loud sounds and/or boosting quiet sounds. So, everything trends toward the same volume. i.e. Compression is used in modern musical releases to make them “constantly loud”.
You’ll probably have to experiment with the settings. From what you are saying, you’ll probably want a fairly high compression ratio, and you’ll probably want a low (high negative value) noise floor. The nose floor setting is designed to prevent the boosting of unwanted background noise.
Also, click Make-up gain, so that you boost quiet sounds rather than reduce loud sounds.
You can also apply compression more than once in increase the effect, and there are LOTs of other compression plug-ins on the Internet.
Don’t expect miracles… If are trying to hear a background conversation and you can’t hear it now, it’s unlikely that you’ll be able to fix that. But if you can clearly hear the background noise, compression should boost it.
Another thing you can try is the Hard Limiter effect. (The Hard Limiter may be one of the optional downloads. I’m not sure.) A limiter limits (or reduces) the loud parts. So, you can apply a limiter (which only affects the loud parts) and then boost everything with the amplify effect. Again, you can apply this effect again after re-boosting the volume. (The limiter will tend to distort loud parts if you over-do it.)