[FFmpeg-user] delay time in live ultrasound converter

Michael Koch astroelectronic at t-online.de
Sat Apr 18 19:48:05 EEST 2020

Am 18.04.2020 um 18:25 schrieb Ted Park:
> I don't know where I can find bats nearby so I couldn't try it but how
> does it work? The book makes it sound like you can use any mic, even
> one built into a laptop for this? I suppose that's plausible looking
> at a typical mic's frequency response graph, they are just cut off at
> 20khz, and don't roll off after 20khz like I thought they would, but
> what about the sample rate? At 44.1kHz doesn't that mean anything over
> 22khz is more aliasing or harmonic distortion than an actual recording
> of bat sounds?

The sounds of those bats that I did record were in the 12kHz to 15kHz 
range. 44.1kHz sample rate is sufficient. I did use two Rode NT1 
microphones, connected to a Tascam DR-70D recorder. If I record the 
ultrasound in the recorder, I use 48kHz sample rate. If live processing 
is required, I connect the Tascam's output to my notebook's audio input, 
which has only 44.1kHz sample rate. That works as well. It is important 
that you disable the low pass filter in the Windows control panel 
(properties of the microphone).


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