File:Audio passthrough.png

This flowgraph takes audio from the audio source, squares it, to get something proportional to the instantaneous power, then low-pass filters it to approximate an averaged-out power, applies a Threshold to it. The latter starts outputting 1s as soon as the smoothed power crosses 10% of the maximum power, and turns back to generating 0s when it falls below 5%.

The resulting stream of 1s and 0s is multiplied with a 440 Hz tone and then fed into an Audio Sink, allowing the user to hear a tone for as long as there's enough sound at the input.