[FFmpeg-user] Multiply audio samples

[Michael Koch]

> Filter inputs will be auto-converted from any non-float formats to 
> float or double one. Float/double formats are in [-1 .. +1] interval. 

Thank you very much for the amultiply filter, it works great!

Here is an example for an ultrasonic converter which downconverts the 
15kHz - 25kHz band to the 0 - 10kHz band.

First make an input file for testing. This is a 2 second 19kHz tone 
followed by 2 seconds silence:

c://ffmpeg/ffmpeg -f lavfi -i 
"sine=frequency=19000:sample_rate=48000:duration=2" -af apad -t 4 
ultrasonic.wav

Then use the downconverter:

c://ffmpeg/ffmpeg -i ultrasonic.wav -f lavfi -i 
"sine=frequency=15000:sample_rate=48000" -filter_complex 
"[0]highpass=f=15000,highpass=f=15000,highpass=f=15000,highpass=f=15000[sound];[1]volume=8[sine];[sound][sine]amultiply[mixed];[mixed]lowpass=f=10000,lowpass=f=10000,lowpass=f=10000,lowpass=f=10000" 
out.wav

Michael