I have received a voice note over WhatsApp from someone, and I have noticed there is another person speaking on the background. The background voice is much quieter than the person recording the voice note. Is it possible to separate the foreground voice from the background, so that I can amplify the latter to hear it more clearly?
~~You could potentially silence the background voice only when the primary voice isn't speaking using a cleverly calibrated Gate. Another suggestion would be iZotope RX type tools, which I believe you can try on demo before buying.~~
*edit: my mistake! read too quickly and thought they were trying to eliminate the bg voice.
To amplify the bg voice, one could use the opposite of a gate - an expander. set the threshold just below the volume of the low/bg speaking voice, and set it to increase in db by the amount that is the difference of the main speaking voice. then, to keep the main speaking voice from blowing the doors off the place (it will also trip the expander, naturally), set a compressor with a high ratio and quick attack or better, a limiter, to even out the voices. This won't take away the primary voice, however. Besides some clever automation or editing depending on what DAW you're using (assuming you're using one), this won't be easily achievable.
If you are able to use a DAW, and the conversation isn't terribly long, the best course of action is likely to chop out the primary speaker's voice then raise the gain of the remaining recording overall.