[FFmpeg-trac] #2759(undetermined:closed): Audio equalizer filter problem - clipping with negative gain

[FFmpeg]

#2759: Audio equalizer filter problem  - clipping with negative gain
-------------------------------------+-------------------------------------
             Reporter:  Ajaja        |                    Owner:
                 Type:  defect       |                   Status:  closed
             Priority:  normal       |                Component:
              Version:  git-master   |  undetermined
             Keywords:               |               Resolution:  invalid
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
-------------------------------------+-------------------------------------

Comment (by Ajaja):

 Yes, it not normalaized (-0.989990...0.989990).  But problem is not in
 source. With +0.1dB gain there is no any messages:
 {{{
 % ffmpeg -i noise.wav -af equalizer=2000:q:1:0.1  noise3.wav
 ...
 Guessed Channel Layout for  Input Stream #0.0 : mono
 Input #0, wav, from 'noise.wav':
   Metadata:
     encoder         : Lavf55.11.100
   Duration: 00:01:00.00, bitrate: 705 kb/s
     Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, mono,
 s16, 705 kb/s
 Output #0, wav, to 'noise2.wav':
   Metadata:
     ISFT            : Lavf55.11.100
     Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, mono,
 s16, 705 kb/s
 Stream mapping:
   Stream #0:0 -> #0:0 (pcm_s16le -> pcm_s16le)
 Press [q] to stop, [?] for help
 size=    5168kB time=00:01:00.00 bitrate= 705.6kbits/s
 video:0kB audio:5168kB subtitle:0 global headers:0kB muxing overhead
 0.001512%
 }}}

 Stats after +0.1dB:
 {{{
 % ffmpeg -i noise3.wav -filter:a "astats" -vn -f null NUL
 ...
 [Parsed_astats_0 @ 00000000026486c0] Overall
 [Parsed_astats_0 @ 00000000026486c0] DC offset: 0.000367
 [Parsed_astats_0 @ 00000000026486c0] Min level: -0.997406
 [Parsed_astats_0 @ 00000000026486c0] Max level: 0.997650
 }}}

 All OK. It's -0.997406..0.997650 now, little gain and no clipping
 messages.

 Let's test normilized sourse:
 {{{
 % sox noise.wav noise4.wav norm
 ...
 % ffmpeg -i noise4.wav -filter:a "astats" -vn -f null NUL
 ...
 [Parsed_astats_0 @ 00000000024e86c0] Overall
 [Parsed_astats_0 @ 00000000024e86c0] DC offset: 0.000371
 [Parsed_astats_0 @ 00000000024e86c0] Min level: -1.000000
 [Parsed_astats_0 @ 00000000024e86c0] Max level: 0.999969

 % ffmpeg -i noise4.wav -af equalizer=2000:q:1:-5 -y noise5.wav
 ....
 Guessed Channel Layout for  Input Stream #0.0 : mono
 Input #0, wav, from 'noise4.wav':
   Duration: 00:01:00.00, bitrate: 705 kb/s
     Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, mono,
 s16, 705 kb/s
 Output #0, wav, to 'noise5.wav':
   Metadata:
     ISFT            : Lavf55.11.100
     Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, mono,
 s16, 705 kb/s
 Stream mapping:
   Stream #0:0 -> #0:0 (pcm_s16le -> pcm_s16le)
 Press [q] to stop, [?] for help
 clipping
     Last message repeated 679 times
 clipping  100kB time=00:00:01.16 bitrate= 706.2kbits/s
     Last message repeated 643 times
 clipping  196kB time=00:00:02.27 bitrate= 705.9kbits/s
     Last message repeated 651 times
 ....
 }}}
 clipping again.

-- 
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2759#comment:5>
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