0723-1 sound (3.3s, 26 kb mp3).
Time vs. frequency plot. Pitch lines are clearly visible,
as well as the main resonance near 3800 hz (audio).
This corresponds (x16) to an ultrasound resonnance of 60.8 khz.
The pitch lines are spaced about 200 hz apart (10 per 2 khz) in the audio plot,
so they are actually spaced 3.2 khz apart.
The pitch frequency is the vibration frequency of the bat's vocal cords.
This is evidence that bats selectively amplify higher harmonics of their basic
pitch to produce ultrasounds. The basic pitch, if indeed at 3.2 khz,
is in the audible range but is very much suppressed.
Picture 5 -- Time axis in audio samples, 32000 samples = 1 sec
At a sample rate of 32000, 50 samples last 50/32000 = .0015625 seconds.
Between samples 80 and 130 there are approx. 6 cycles,
so the dominant audio frequency in that region is 6/.0015625 = 3840 hz.
The bat is actually emitting at 16*3840 = 61440 hz.