[FFmpeg-user] silenceremove use

[Paul B Mahol]

On 2/19/20, Ted Park <kumowoon1025 at gmail.com> wrote:
>> Is there anyone who has experience with the silenceremove filter? I'm
>> trying to remove long silences from recordings i made on my phone. The
>> silences are actually a constant noise because of the microphone gain is
>> set to 5.0x. (The playback meter in Audacity says the noise is around -48
>> to 42 dB). It is around 9 hours in duration. 1,1 GB large, signed 16 bit
>> little endian mono 16 kHz wave file. Audacity says it's 32 bit float wave
>> file though.
>
> Hey there,
> As you’ve noticed you pretty much need to know the basic “profile,” I guess,
> of the silence in your audio for best results. You could use the show volume
> filter with ffplay,
> % ffplay -f lavfi -i “amovie=$INPUT,showvolume"
> To get a general idea of what the noise is like, and apply the options
> accordingly.
> e.g. 	Use the levels of the silence/noise sections for the level options,
> setting -20db would cut out a lot more than noise, I think; see if there are
> short periods of noise, other than background noise, but still noise, and
> see how long those are to set a value for the duration options; also see if
> using peak and a window of 10 seconds makes sense (It might not, even if you
> set a more sensible value for the threshold, basically I think that would
> make it treat anything as silence if in a 10 second window it rises above
> the threshold even once)

If audio was in any way processed prior to silence removal, like in
this case with gain, you will certainly get poor results.