Two generated tones creates a side tone - how to avoid the side tone
I have tried the following:


Launch Audacity.
Generate a 15000 Hz tone in the track created by default.
Add a new track.
Generate a 15400 Hz tone in the new track.


A lower frequency tone appears during playback.

The reason is that both tracks have high levels, so their sum exceeds 1.0; and Audacity applies clipping or limiting. This non-linear operation is what creates the overtone.

Simply decrease the level of both tracks to -6dB (or use an amplitude of 0.5 during signal generation) to make the overtone disappear.