Resources for THEORY AND PRACTICE OF PIANO TUNING
In a double beat rate there is more than one distinct beat rate in a single beating partial, which can lead to confusion over the tempering of the interval. In this example of an isolated partial with a double beat, the beat rates are 5 Hz and 10 Hz.
Headphones are necessary for all these demonstrations.
Make sure your volume is turned down before you listen to these clips, and adjust up carefully to a comfortable level.