Body: <p>I'm merging together a bunch of videos (30 so far) into a &quot;Brady Bunch&quot; style amalgam using ffmpeg, and I've got that working reasonably well.  The last big problem is the background noise.  Everybody recorded at different locations, and some of those locations had computer fans in the background and some had air conditioners, and when you add them all together, the summed background noise is really noticeable.</p>
  <p>I'm doing everything with complex filters, here's a rough idea what I've got going on:</p>
  <pre><code>color=size=1920x1080:c=0x000080 [base]
  [0:a]volume=0.90,aresample=async=1:first_pts=0[aud0]
  [1:a]volume=2.08,aresample=async=1:first_pts=0[aud1]
  [2:a]volume=1.48,aresample=async=1:first_pts=0[aud2]
  [3:a]volume=2.53,aresample=async=1:first_pts=0[aud3]
  [4:a]volume=1.34,aresample=async=1:first_pts=0[aud4]
  [5:a]volume=1.81,aresample=async=1:first_pts=0[aud5]
  (and a bunch more adjusting the volume of each input video)
  [28:a]volume=1.06,aresample=async=1:first_pts=0[aud28]
  (and then we start the videos, at first only a subset are visible and then the large group
  joins in, so I &quot;zoom in&quot; on the small group and then expand to bring in everyone else
  when it's their turn)
  [0:v] scale=w=if(lte(n\,1200.00)\,576\,if(lte(n\,1410.00)\,576.0-288.00*(n-1200.00)/210.00\,288)):h=if(lte(n\,1200.00)\,324\,if(lte(n\,1410.00)\,324.0-162.00*(n-1200.00)/210.00\,162)):eval=frame [clip0]
  [base][clip0] overlay=shortest=1:x=if(lte(n\,1000.00)\,-608\,if(lte(n\,1175.00)\,-608.0+624.00*(n-1000.00)/175.00\,16)):y=if(lte(n\,1000.00)\,-342\,if(lte(n\,1175.00)\,-342.0+369.00*(n-1000.00)/175.00\,27)) [over0]
  [1:v] crop=870:917:553:163,scale=w=if(lte(n\,1198.80)\,307\,if(lte(n\,1408.59)\,307.0-123.00*(n-1198.80)/209.79\,184)):h=if(lte(n\,1198.80)\,324\,if(lte(n\,1408.59)\,324.0-130.00*(n-1198.80)/209.79\,194)):eval=frame [clip1]
  [over0][clip1] overlay=shortest=1:x=if(lte(n\,1000.00)\,166\,if(lte(n\,1175.00)\,166.0+222.00*(n-1000.00)/175.00\,388)):y=if(lte(n\,1000.00)\,-342\,if(lte(n\,1175.00)\,-342.0+353.00*(n-1000.00)/175.00\,11)) [over1]
  (you get the idea)
  (and then I merge all the audio together)
  [aud0][aud1][aud2][aud3][aud4][aud5][aud6][aud7][aud8][aud9][aud10][aud11][aud12][aud13][aud14][aud15][aud16][aud17][aud18][aud19][aud20][aud21][aud22][aud23][aud24][aud25][aud26][aud27][aud28]amix=inputs=29[a]
  [a]adelay=delays=200:all=1[b]
  (I've run a first pass of loudnorm to measure the output levels, and I send them back in)
  [b]loudnorm=linear=true:I=-14:LRA=11:tp=-2:measured_I=-30.18:measured_LRA=17.80:measured_tp=-15.23:measured_thresh=-41.39:offset=-0.77:print_format=summary[level]
  </code></pre>
  <p>What I'm thinking, is that most everybody starts out with a few seconds of silence.  It seems like I should be able to measure the audio in that segment, and then use it to filter out the background per stream.</p>
  <p>It seems like <a href="http://underpop.online.fr/f/ffmpeg/help/afftdn.htm.gz" rel="nofollow noreferrer">afftdn</a> will do that, but I cannot for the life of me figure out how to use it.  Apparently I need to <a href="http://underpop.online.fr/f/ffmpeg/help/sendcmd_002c-asendcmd.htm.gz" rel="nofollow noreferrer">send commands to it</a>, as I have read <a href="https://video.stackexchange.com/questions/29274/how-can-you-use-ffmpegs-afftdn-sn-flag-to-sample-noise-from-a-reference-noise">here</a>, but it's not at all clear how I make that work inside my complex filter.  Something to do with ZMQ?  Is ZMQ what's happening with all those &quot;@n&quot;s?</p>
  <p>EDIT</p>
  <p>The answer that Gyan refers to is this:</p>
  <pre><code>ffmpeg -i in -i profile -filter_complex &quot;[1][0]concat=n=2:v=0:a=1,asendcmd=c='0.0 afftdn@n sn start; 1.0 afftdn@n sn stop',afftdn@n,atrim=1,asetpts=PTS-STARTPTS&quot; noiseout.wav
  </code></pre>
  <p>Let me see if I can break this down and understand it.</p>
  <p>In that question, [1] is the noise profile and [0] is the input audio.</p>
  <pre><code>[1][0]concat=n=2:v=0:a=1
  </code></pre>
  <p>Means concatenate the two audio streams, noise profile first, and generate as an output only an audio stream.</p>
  <p>Then we get ready to send commands to afftdn, using the ZMQ syntax:</p>
  <pre><code>asendcmd=c='0.0 afftdn@n sn start; 1.0 afftdn@n sn stop'
  </code></pre>
  <p>In ZMQ, you have to give a filter an id so it knows which filter you are sending the command to.  In this case, we've assigned the one and only afftdn the id 'n', and we are telling it to start measuring the noise profile at time 0 (the default so not specified) and stop measuring at time 1.</p>
  <p>So now we actually invoke the afftdn filter:</p>
  <pre><code>afftdn@n
  </code></pre>
  <p>Then we trim off that first second of the audio stream (which is just the noise profile):</p>
  <pre><code>atrim=1
  </code></pre>
  <p>And finally, we want to reset the timestamp of the audio stream so that 'zero' is the new position (after the noise profile):</p>
  <pre><code>asetpts=PTS-STARTPTS
  </code></pre>
  <p>SO</p>
  <p>For now at least, I'm going to always use the first second of the audio as my noise profile.  Since it's already at the start of the audio, I don't need to isolate it, reset its timestamp, and concatenate it at the start of the audio (right?).  So taking audio stream [aud0], I can do this:</p>
  <pre><code>[aud0]asendcmd=c='0.0 afftdn@n sn start; 1.0 afftdn@n sn stop',afftdn@n[faud0]
  </code></pre>
  <p>and then send [faud0] into the 'amix' instead of [aud0]</p>
  <p>Yes?</p>
  <p>SECOND EDIT</p>
  <p>I'm now duplicating the first second of each audio stream and appending it on the front, just like in Gyan's answer.  Here is one such audio stream:</p>
  <pre><code>[19:a]volume=31.59,aresample=async=1:first_pts=0[aud19]
  [aud19]asplit[aud19a][aud19b]
  [aud19a]atrim=0:1[aud19c]
  [aud19c][aud19b]concat=n=2:v=0:a=1,asendcmd=c='0.0 afftdn@t sn start; 1.0 afftdn@t sn stop',afftdn@t=nr=90,atrim=1,asetpts=PTS-STARTPTS[aud19d]
  </code></pre>
  <p>Notice that since I've got so many audio streams, and each one has its own afftdn filter, I've given them all separate ids.</p>
  <p>And still, the output audio does not sound significantly different from when I started!</p>
  <p>THIRD EDIT</p>
  <p>So I grabbed one of the videos that has a lot of noise at the front, kind of sounds like lots of air moving, maybe some 60 Hz fan noise too.  I extracted the first 9 seconds into a file I cleverly named &quot;<a href="https://drive.google.com/file/d/1CUj00QIF0iR_AgYZ_I2I_aVmYqJX5aHM/view?usp=sharing" rel="nofollow noreferrer">trim.wav</a>&quot;.  I then ran ffmpeg twice, once normally, and once to output just the noise.  The &quot;<a href="https://drive.google.com/file/d/1HLP9tL4Y20rbTKuJA8yWJK-4BQS_Z901/view?usp=sharing" rel="nofollow noreferrer">just noise</a>&quot; file is totally devoid of sound, as if it didn't find any noise to work with.  And as expected, the (supposedly) <a href="https://drive.google.com/file/d/1vuK1F2tH1m4NWYuzOxtbnMeG1VU9UH8G/view?usp=sharing" rel="nofollow noreferrer">processed file</a> sounds identical to the input.</p>
  <p>Here are my command lines:</p>
  <pre><code>c:ffmpeg -y -i trim.wav -filter_complex &quot;[0:a]asplit[aud0a][aud0b];[aud0a]atrim=0:1[aud0c];[aud0c][aud0b]concat=n=2:v=0:a=1,asendcmd=c='0.0 afftdn@aa sn start; 1.0 afftdn@aa sn stop',afftdn@aa,atrim=1,asetpts=PTS-STARTPTS[aud0d]&quot; -map &quot;[aud0d]&quot; processed.wav
  c:ffmpeg -y -i trim.wav -filter_complex &quot;[0:a]asplit[aud0a][aud0b];[aud0a]atrim=0:1[aud0c];[aud0c][aud0b]concat=n=2:v=0:a=1,asendcmd=c='0.0 afftdn@aa sn start; 1.0 afftdn@aa sn stop',afftdn@aa=om=n,atrim=1,asetpts=PTS-STARTPTS[aud0d]&quot; -map &quot;[aud0d]&quot; noise.wav
  </code></pre>
  <p>Here's what ffmpeg had to say:</p>
  <pre><code>ffmpeg version git-2020-08-07-fab00b0 Copyright (c) 2000-2020 the FFmpeg developers
   built with gcc 10.2.1 (GCC) 20200805
   configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libsrt --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-libgsm --enable-librav1e --disable-w32threads --enable-libmfx --enable-ffnvcodec --enable-cuda-llvm --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf
   libavutil      56. 58.100 / 56. 58.100
   libavcodec     58. 99.100 / 58. 99.100
   libavformat    58. 49.100 / 58. 49.100
   libavdevice    58. 11.101 / 58. 11.101
   libavfilter     7. 87.100 /  7. 87.100
   libswscale      5.  8.100 /  5.  8.100
   libswresample   3.  8.100 /  3.  8.100
   libpostproc    55.  8.100 / 55.  8.100
  Guessed Channel Layout for Input Stream #0.0 : stereo
  Input #0, wav, from 'trim.wav':
   Metadata:
   encoder         : Lavf58.49.100
   Duration: 00:00:09.00, bitrate: 1411 kb/s
   Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, stereo, s16, 1411 kb/s
  Stream mapping:
  Stream #0:0 (pcm_s16le) -&gt; asplit
   asetpts -&gt; Stream #0:0 (pcm_s16le)
  Output #0, wav, to 'processed.wav':
   Metadata:
    ISFT            : Lavf58.49.100
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, stereo, s16, 1411 kb/s
    Metadata:
     encoder         : Lavc58.99.100 pcm_s16le
       [afftdn @ 00000261c3b81400] bn=4 -6 -10 -12 -12 -14 -17 -23 -24 -24 -24 -24 -24 -24 -15
       [afftdn @ 00000261c3b81400] bn=5 -4 -8 -10 -11 -14 -18 -23 -24 -24 -24 -24 -24 -24 -15
    size=    1545kB time=00:00:08.97 bitrate=1411.3kbits/s speed= 150x
  video:0kB audio:1545kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.004929%
  </code></pre>
  <p>FOURTH EDIT</p>
  <p>Based on comments, I tried adjusting the noise floor and also using just a single audio track.  I ran these commands:</p>
  <pre><code>c:ffmpeg -y -i trim.wav -filter_complex &quot;[0:a]asendcmd=c='0.0 afftdn@aa sn start; 1.0 afftdn@aa sn stop',afftdn@aa=nr=90[aud0d]&quot; -map &quot;[aud0d]&quot; output-nr90.wav
  c:ffmpeg -y -i trim.wav -filter_complex &quot;[0:a]asendcmd=c='0.0 afftdn@aa sn start; 1.0 afftdn@aa sn stop',afftdn@aa=nr=1[aud0d]&quot; -map &quot;[aud0d]&quot; output-nr1.wav
  c:ffmpeg -y -i trim.wav -filter_complex &quot;[0:a]asendcmd=c='0.0 afftdn@aa sn start; 1.0 afftdn@aa sn stop',afftdn@aa=nr=90:nf=-20[aud0d]&quot; -map &quot;[aud0d]&quot; output-nr90-nf20.wav
  c:ffmpeg -y -i trim.wav -filter_complex &quot;[0:a]asendcmd=c='0.0 afftdn@aa sn start; 1.0 afftdn@aa sn stop',afftdn@aa=nr=1:nf=-20[aud0d]&quot; -map &quot;[aud0d]&quot; output-nr1-nf20.wav
  c:ffmpeg -y -i trim.wav -filter_complex &quot;[0:a]asendcmd=c='0.0 afftdn@aa sn start; 1.0 afftdn@aa sn stop',afftdn@aa=nr=90:nf=-80[aud0d]&quot; -map &quot;[aud0d]&quot; output-nr90-nf80.wav
  c:ffmpeg -y -i trim.wav -filter_complex &quot;[0:a]asendcmd=c='0.0 afftdn@aa sn start; 1.0 afftdn@aa sn stop',afftdn@aa=nr=1:nf=-80[aud0d]&quot; -map &quot;[aud0d]&quot; output-nr1-nf80.wav
  </code></pre>
  <p>and for the most part I don't hear any noticeable difference.  However, with the filter 'afftdn@aa=nr=90:nf=-20' I hear what sounds like a 1-second reprieve from the noise at the very beginning of <a href="https://drive.google.com/file/d/1VbcEuPaQ8NtB0WphG2fceDlM2kBse1kY/view?usp=sharing" rel="nofollow noreferrer">the audio</a>, as if that noise was being filtered out while leaving all of the noise in the rest of the track.  Am I just using the wrong filter?  Is my noise not the type of noise that afftdn is effective on?  Or am I somehow misusing the filter so it's only filtering the first second?  For reference, here is the <a href="https://drive.google.com/file/d/1CUj00QIF0iR_AgYZ_I2I_aVmYqJX5aHM/view?usp=sharing" rel="nofollow noreferrer">input track</a>.</p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-12-01T13:03:05.767Z
Comments.Text: You would use the 2nd method in my answer. Instead of a separate profile input, you would split each audio stream into two. From one copy, use atrim to isolate a portion useful for profiling, then reset its timestamps using asetpts. Then concat it with the 2nd full copy. Execute commands using asendcmd as shown in the answer, then afftdn. Then use atrim to discard that segment and restore timestamps.
Comments.UserDisplayName: Gyan
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-12-01T20:10:52.723Z
Comments.Text: Something doesn't seem quite right.  If I change the final afftdn filter to afftdn@n=om=n (to just hear the noise) it works exactly as expected (gives me just the noise) but I'm not noticing a big difference in audio output even when I use afftdn@n=nr=30
Comments.UserDisplayName: Betty Crokker
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-12-01T20:25:14.433Z
Comments.Text: No difference in output even with afftdn@n=nr=80
Comments.UserDisplayName: Betty Crokker
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-12-02T05:14:01.420Z
Comments.Text: Try with a minimal command (say, 2 audio streams) and check. Add full command and full logs if it doesn't work.
Comments.UserDisplayName: Gyan
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-12-03T01:53:50.473Z
Comments.Text: @Gyan Thanks for your help with this!  I've edited my original question, and uploaded some smaller WAV files to my Google Drive so you have everything that I'm working with.
Comments.UserDisplayName: Betty Crokker
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2021-01-23T23:52:36.547Z
Comments.Text: @PaulB.Mahol I agree that the split/concat seems like extra work in this case, unfortunately the syntax here is so tricky that I have no idea how to make afftdn work without splitting the stream.  Can you help provide the syntax I would need?  Thanks!
Comments.UserDisplayName: Betty Crokker
Tags: <ffmpeg><filter><noise>
Title: Sampling and using afftdn with ffmpeg - how with complex filters?
UserDisplayName: Betty Crokker
ThreadText: # Sampling and using afftdn with ffmpeg - how with complex filters?
  
  (Asked by: username_0 on 2020-12-01)
  
  I'm merging together a bunch of videos (30 so far) into a "Brady Bunch" style amalgam using ffmpeg, and I've got that working reasonably well. The last big problem is the background noise. Everybody recorded at different locations, and some of those locations had computer fans in the background and some had air conditioners, and when you add them all together, the summed background noise is really noticeable.
  
  I'm doing everything with complex filters, here's a rough idea what I've got going on:
  
  ```
  color=size=1920x1080:c=0x000080 [base]
  [0:a]volume=0.90,aresample=async=1:first_pts=0[aud0]
  [1:a]volume=2.08,aresample=async=1:first_pts=0[aud1]
  [2:a]volume=1.48,aresample=async=1:first_pts=0[aud2]
  [3:a]volume=2.53,aresample=async=1:first_pts=0[aud3]
  [4:a]volume=1.34,aresample=async=1:first_pts=0[aud4]
  [5:a]volume=1.81,aresample=async=1:first_pts=0[aud5]
  (and a bunch more adjusting the volume of each input video)
  [28:a]volume=1.06,aresample=async=1:first_pts=0[aud28]
  (and then we start the videos, at first only a subset are visible and then the large group
  joins in, so I "zoom in" on the small group and then expand to bring in everyone else
  when it's their turn)
  [0:v] scale=w=if(lte(n\,1200.00)\,576\,if(lte(n\,1410.00)\,576.0-288.00*(n-1200.00)/210.00\,288)):h=if(lte(n\,1200.00)\,324\,if(lte(n\,1410.00)\,324.0-162.00*(n-1200.00)/210.00\,162)):eval=frame [clip0]
  [base][clip0] overlay=shortest=1:x=if(lte(n\,1000.00)\,-608\,if(lte(n\,1175.00)\,-608.0+624.00*(n-1000.00)/175.00\,16)):y=if(lte(n\,1000.00)\,-342\,if(lte(n\,1175.00)\,-342.0+369.00*(n-1000.00)/175.00\,27)) [over0]
  [1:v] crop=870:917:553:163,scale=w=if(lte(n\,1198.80)\,307\,if(lte(n\,1408.59)\,307.0-123.00*(n-1198.80)/209.79\,184)):h=if(lte(n\,1198.80)\,324\,if(lte(n\,1408.59)\,324.0-130.00*(n-1198.80)/209.79\,194)):eval=frame [clip1]
  [over0][clip1] overlay=shortest=1:x=if(lte(n\,1000.00)\,166\,if(lte(n\,1175.00)\,166.0+222.00*(n-1000.00)/175.00\,388)):y=if(lte(n\,1000.00)\,-342\,if(lte(n\,1175.00)\,-342.0+353.00*(n-1000.00)/175.00\,11)) [over1]
  (you get the idea)
  (and then I merge all the audio together)
  [aud0][aud1][aud2][aud3][aud4][aud5][aud6][aud7][aud8][aud9][aud10][aud11][aud12][aud13][aud14][aud15][aud16][aud17][aud18][aud19][aud20][aud21][aud22][aud23][aud24][aud25][aud26][aud27][aud28]amix=inputs=29[a]
  [a]adelay=delays=200:all=1[b]
  (I've run a first pass of loudnorm to measure the output levels, and I send them back in)
  [b]loudnorm=linear=true:I=-14:LRA=11:tp=-2:measured_I=-30.18:measured_LRA=17.80:measured_tp=-15.23:measured_thresh=-41.39:offset=-0.77:print_format=summary[level]
  
  ```
  
  What I'm thinking, is that most everybody starts out with a few seconds of silence. It seems like I should be able to measure the audio in that segment, and then use it to filter out the background per stream.
  
  It seems like [afftdn](http://underpop.online.fr/f/ffmpeg/help/afftdn.htm.gz) will do that, but I cannot for the life of me figure out how to use it. Apparently I need to [send commands to it](http://underpop.online.fr/f/ffmpeg/help/sendcmd_002c-asendcmd.htm.gz), as I have read [here](https://video.stackexchange.com/questions/29274/how-can-you-use-ffmpegs-afftdn-sn-flag-to-sample-noise-from-a-reference-noise), but it's not at all clear how I make that work inside my complex filter. Something to do with ZMQ? Is ZMQ what's happening with all those "@n"s?
  
  EDIT
  
  The answer that username_1 refers to is this:
  
  ```
  ffmpeg -i in -i profile -filter_complex "[1][0]concat=n=2:v=0:a=1,asendcmd=c='0.0 afftdn@n sn start; 1.0 afftdn@n sn stop',afftdn@n,atrim=1,asetpts=PTS-STARTPTS" noiseout.wav
  
  ```
  
  Let me see if I can break this down and understand it.
  
  In that question, [1] is the noise profile and [0] is the input audio.
  
  ```
  [1][0]concat=n=2:v=0:a=1
  
  ```
  
  Means concatenate the two audio streams, noise profile first, and generate as an output only an audio stream.
  
  Then we get ready to send commands to afftdn, using the ZMQ syntax:
  
  ```
  asendcmd=c='0.0 afftdn@n sn start; 1.0 afftdn@n sn stop'
  
  ```
  
  In ZMQ, you have to give a filter an id so it knows which filter you are sending the command to. In this case, we've assigned the one and only afftdn the id 'n', and we are telling it to start measuring the noise profile at time 0 (the default so not specified) and stop measuring at time 1.
  
  So now we actually invoke the afftdn filter:
  
  ```
  afftdn@n
  
  ```
  
  Then we trim off that first second of the audio stream (which is just the noise profile):
  
  ```
  atrim=1
  
  ```
  
  And finally, we want to reset the timestamp of the audio stream so that 'zero' is the new position (after the noise profile):
  
  ```
  asetpts=PTS-STARTPTS
  
  ```
  
  SO
  
  For now at least, I'm going to always use the first second of the audio as my noise profile. Since it's already at the start of the audio, I don't need to isolate it, reset its timestamp, and concatenate it at the start of the audio (right?). So taking audio stream [aud0], I can do this:
  
  ```
  [aud0]asendcmd=c='0.0 afftdn@n sn start; 1.0 afftdn@n sn stop',afftdn@n[faud0]
  
  ```
  
  and then send [faud0] into the 'amix' instead of [aud0]
  
  Yes?
  
  SECOND EDIT
  
  I'm now duplicating the first second of each audio stream and appending it on the front, just like in username_1's answer. Here is one such audio stream:
  
  ```
  [19:a]volume=31.59,aresample=async=1:first_pts=0[aud19]
  [aud19]asplit[aud19a][aud19b]
  [aud19a]atrim=0:1[aud19c]
  [aud19c][aud19b]concat=n=2:v=0:a=1,asendcmd=c='0.0 afftdn@t sn start; 1.0 afftdn@t sn stop',afftdn@t=nr=90,atrim=1,asetpts=PTS-STARTPTS[aud19d]
  
  ```
  
  Notice that since I've got so many audio streams, and each one has its own afftdn filter, I've given them all separate ids.
  
  And still, the output audio does not sound significantly different from when I started!
  
  THIRD EDIT
  
  So I grabbed one of the videos that has a lot of noise at the front, kind of sounds like lots of air moving, maybe some 60 Hz fan noise too. I extracted the first 9 seconds into a file I cleverly named "[trim.wav](https://drive.google.com/file/d/1CUj00QIF0iR_AgYZ_I2I_aVmYqJX5aHM/view?usp=sharing)". I then ran ffmpeg twice, once normally, and once to output just the noise. The "[just noise](https://drive.google.com/file/d/1HLP9tL4Y20rbTKuJA8yWJK-4BQS_Z901/view?usp=sharing)" file is totally devoid of sound, as if it didn't find any noise to work with. And as expected, the (supposedly) [processed file](https://drive.google.com/file/d/1vuK1F2tH1m4NWYuzOxtbnMeG1VU9UH8G/view?usp=sharing) sounds identical to the input.
  
  Here are my command lines:
  
  ```
  c:ffmpeg -y -i trim.wav -filter_complex "[0:a]asplit[aud0a][aud0b];[aud0a]atrim=0:1[aud0c];[aud0c][aud0b]concat=n=2:v=0:a=1,asendcmd=c='0.0 afftdn@aa sn start; 1.0 afftdn@aa sn stop',afftdn@aa,atrim=1,asetpts=PTS-STARTPTS[aud0d]" -map "[aud0d]" processed.wav
  c:ffmpeg -y -i trim.wav -filter_complex "[0:a]asplit[aud0a][aud0b];[aud0a]atrim=0:1[aud0c];[aud0c][aud0b]concat=n=2:v=0:a=1,asendcmd=c='0.0 afftdn@aa sn start; 1.0 afftdn@aa sn stop',afftdn@aa=om=n,atrim=1,asetpts=PTS-STARTPTS[aud0d]" -map "[aud0d]" noise.wav
  
  ```
  
  Here's what ffmpeg had to say:
  
  ```
  ffmpeg version git-2020-08-07-fab00b0 Copyright (c) 2000-2020 the FFmpeg developers
   built with gcc 10.2.1 (GCC) 20200805
   configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libsrt --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-libgsm --enable-librav1e --disable-w32threads --enable-libmfx --enable-ffnvcodec --enable-cuda-llvm --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf
   libavutil      56. 58.100 / 56. 58.100
   libavcodec     58. 99.100 / 58. 99.100
   libavformat    58. 49.100 / 58. 49.100
   libavdevice    58. 11.101 / 58. 11.101
   libavfilter     7. 87.100 /  7. 87.100
   libswscale      5.  8.100 /  5.  8.100
   libswresample   3.  8.100 /  3.  8.100
   libpostproc    55.  8.100 / 55.  8.100
  Guessed Channel Layout for Input Stream #0.0 : stereo
  Input #0, wav, from 'trim.wav':
   Metadata:
   encoder         : Lavf58.49.100
   Duration: 00:00:09.00, bitrate: 1411 kb/s
   Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, stereo, s16, 1411 kb/s
  Stream mapping:
  Stream #0:0 (pcm_s16le) -> asplit
   asetpts -> Stream #0:0 (pcm_s16le)
  Output #0, wav, to 'processed.wav':
   Metadata:
    ISFT            : Lavf58.49.100
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, stereo, s16, 1411 kb/s
    Metadata:
     encoder         : Lavc58.99.100 pcm_s16le
       [afftdn @ 00000261c3b81400] bn=4 -6 -10 -12 -12 -14 -17 -23 -24 -24 -24 -24 -24 -24 -15
       [afftdn @ 00000261c3b81400] bn=5 -4 -8 -10 -11 -14 -18 -23 -24 -24 -24 -24 -24 -24 -15
    size=    1545kB time=00:00:08.97 bitrate=1411.3kbits/s speed= 150x
  video:0kB audio:1545kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.004929%
  
  ```
  
  FOURTH EDIT
  
  Based on comments, I tried adjusting the noise floor and also using just a single audio track. I ran these commands:
  
  ```
  c:ffmpeg -y -i trim.wav -filter_complex "[0:a]asendcmd=c='0.0 afftdn@aa sn start; 1.0 afftdn@aa sn stop',afftdn@aa=nr=90[aud0d]" -map "[aud0d]" output-nr90.wav
  c:ffmpeg -y -i trim.wav -filter_complex "[0:a]asendcmd=c='0.0 afftdn@aa sn start; 1.0 afftdn@aa sn stop',afftdn@aa=nr=1[aud0d]" -map "[aud0d]" output-nr1.wav
  c:ffmpeg -y -i trim.wav -filter_complex "[0:a]asendcmd=c='0.0 afftdn@aa sn start; 1.0 afftdn@aa sn stop',afftdn@aa=nr=90:nf=-20[aud0d]" -map "[aud0d]" output-nr90-nf20.wav
  c:ffmpeg -y -i trim.wav -filter_complex "[0:a]asendcmd=c='0.0 afftdn@aa sn start; 1.0 afftdn@aa sn stop',afftdn@aa=nr=1:nf=-20[aud0d]" -map "[aud0d]" output-nr1-nf20.wav
  c:ffmpeg -y -i trim.wav -filter_complex "[0:a]asendcmd=c='0.0 afftdn@aa sn start; 1.0 afftdn@aa sn stop',afftdn@aa=nr=90:nf=-80[aud0d]" -map "[aud0d]" output-nr90-nf80.wav
  c:ffmpeg -y -i trim.wav -filter_complex "[0:a]asendcmd=c='0.0 afftdn@aa sn start; 1.0 afftdn@aa sn stop',afftdn@aa=nr=1:nf=-80[aud0d]" -map "[aud0d]" output-nr1-nf80.wav
  
  ```
  
  and for the most part I don't hear any noticeable difference. However, with the filter 'afftdn@aa=nr=90:nf=-20' I hear what sounds like a 1-second reprieve from the noise at the very beginning of [the audio](https://drive.google.com/file/d/1VbcEuPaQ8NtB0WphG2fceDlM2kBse1kY/view?usp=sharing), as if that noise was being filtered out while leaving all of the noise in the rest of the track. Am I just using the wrong filter? Is my noise not the type of noise that afftdn is effective on? Or am I somehow misusing the filter so it's only filtering the first second? For reference, here is the [input track](https://drive.google.com/file/d/1CUj00QIF0iR_AgYZ_I2I_aVmYqJX5aHM/view?usp=sharing).
  
  **Tags:** ffmpeg, filter, noise
  
  > **Comments:**
  > **username_1**: You would use the 2nd method in my answer. Instead of a separate profile input, you would split each audio stream into two. From one copy, use atrim to isolate a portion useful for profiling, then reset its timestamps using asetpts. Then concat it with the 2nd full copy. Execute commands using asendcmd as shown in the answer, then afftdn. Then use atrim to discard that segment and restore timestamps.  
  > **username_0**: Something doesn't seem quite right.  If I change the final afftdn filter to afftdn@n=om=n (to just hear the noise) it works exactly as expected (gives me just the noise) but I'm not noticing a big difference in audio output even when I use afftdn@n=nr=30  
  > **username_0**: No difference in output even with afftdn@n=nr=80  
  > **username_1**: Try with a minimal command (say, 2 audio streams) and check. Add full command and full logs if it doesn't work.  
  > **username_0**: @username_1 Thanks for your help with this!  I've edited my original question, and uploaded some smaller WAV files to my Google Drive so you have everything that I'm working with.  
  > **username_0**: @PaulB.Mahol I agree that the split/concat seems like extra work in this case, unfortunately the syntax here is so tricky that I have no idea how to make afftdn work without splitting the stream.  Can you help provide the syntax I would need?  Thanks!  
  
  ---
  
  ## 0 answers
  
  