Based on the previous results, we know we can reliably split an already-created file using SoX's trim command.
For a refresher: SoX supports ms accuracy as well as supporting two different measurement formats:
trim 2520 28meaning trim 28 seconds, starting from 2520 seconds intrim 2520 =2548meaning trim from 2520 seconds to 2548 seconds- I attempted to trick SoX in to being more precise with
trim 2520.0000 =2548.0000, but it turns out it wasn't neccessary. The MD5 hash oftrim 2520.0000 =2548.0000andtrim 2520 =2548were identical.
Following the same procotol as the FFMPEG tests, we start with the Matlab-generated FLAC file. This time, however, we load it in to an Audio player (QuickTime Player, why not), then play it back while recording with SoX.
In the previous test, a mathematecally generated file was used with tones every 7 seconds, then the file was split in to 7-second segments and each was tested for precision.
In this experiment, the mathematecally generated file is played while SoX records it with /usr/local/bin/sox -V6 -d -c 1 ~/Sox/20160101_000000-0400.n.mp3 trim 0 7 : newfile : restart
-V6set the verbosity to level 6 (all messages including debug)-duse the default audio input (set by OSX)-c 1one channel recording (mono)trim 0 7trim the input from the beginning to 7 seconds: newfilegenerate a new file (adds an incremented number to the filename): restartafter the file is generated, restart the sox command
We come up with two disturbing points from a precision perspective:
- Each segment is not 7 seconds, but is in fact 7.000816 seconds
- When looking at the timing of the recording of tones, it's obvious that SoX regularly fumbles.
- For example: 25 segments will be correct, then #26 will have the tone slightly early. #26-#110 will be the same, then #111 will have the tone earlier still.
- Suspiciously, this is not consistant. Sometimes it will be >100 segments between shifts, sometimes it will be <5.
There are some times where this error shows in Sox: sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
Suspecting that it's related to CPU usage, I switched to wav with the same flags.
sox -V6 -d 20160101_000000-0400.n.wav trim 0 7 : newfile : restart
During the test, the same errors occurred. To be fair, these errors come up most of the time while recording. Here are some examples:
Output File : '20160101_000000-0400.n070.wav'
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Comment : 'Processed by SoX'
sox DBUG trim: position 1 at 0
sox DBUG trim: position 2 at 308700
sox INFO sox: effects chain: input 44100Hz 2 channels (multi) 32 bits unknown length
sox INFO sox: effects chain: trim 44100Hz 2 channels (multi) 32 bits 00:00:07.00
sox INFO sox: effects chain: output 44100Hz 2 channels (multi) 32 bits 00:00:07.00
In:0.00% 00:08:08.20 [00:00:00.00] Out:21.5M [ ====|==== ] Clip:145 sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
In:0.00% 00:08:10.01 [00:00:00.00] Out:21.6M [ | ] Clip:145
sox DBUG wav: Finished writing Wave file, 2469600 data bytes 308700 samples
Output File : '20160101_000000-0400.n097.wav'
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Comment : 'Processed by SoX'
sox DBUG trim: position 1 at 0
sox DBUG trim: position 2 at 308700
sox INFO sox: effects chain: input 44100Hz 2 channels (multi) 32 bits unknown length
sox INFO sox: effects chain: trim 44100Hz 2 channels (multi) 32 bits 00:00:07.00
sox INFO sox: effects chain: output 44100Hz 2 channels (multi) 32 bits 00:00:07.00
In:0.00% 00:11:16.09 [00:00:00.00] Out:29.8M [ | ] Clip:454 sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
In:0.00% 00:11:19.02 [00:00:00.00] Out:29.9M [ | ] Hd:4.7 Clip:454
sox DBUG wav: Finished writing Wave file, 2469600 data bytes 308700 samples
Output File : '20160101_000000-0400.n243.wav'
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Comment : 'Processed by SoX'
sox DBUG trim: position 1 at 0
sox DBUG trim: position 2 at 308700
sox INFO sox: effects chain: input 44100Hz 2 channels (multi) 32 bits unknown length
sox INFO sox: effects chain: trim 44100Hz 2 channels (multi) 32 bits 00:00:07.00
sox INFO sox: effects chain: output 44100Hz 2 channels (multi) 32 bits 00:00:07.00
In:0.00% 00:28:15.57 [00:00:00.00] Out:74.8M [-=====|======] Hd:1.6 Clip:1.65ksox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
In:0.00% 00:28:20.16 [00:00:00.00] Out:75.0M [ | ] Clip:1.65ksox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
The segments are now exactly 7 seconds long, so we know there was some imprecision introduced in the conversion to mp3. Unfortunately, changing this has not solved the underlying problem. Looking in to the timings of the segments, the same pattern occurs: at seemingly random intervals, the tone is earlier than it should be, and earlier than the segment before it.
For the sake of thoroughness, we took local playback out of the picture. The WAV file was loaded on an iPad Air 2 and played through Vox with no other applications running and airplane mode turned on.
Recordings are made with sox -V6 -d 20160101_000000-0400.n.wav trim 0 7 : newfile : restart
With playback on the other device, SoX is still not working in a precise way.
The resulting segments are 7 seconds exactly, but again show the same issue with timing.
Here's a deeper dig in to an example:
- Files 58-81 have the tone in the exact same spot.
20160101_000000-0400.n082.wavhas the tone 600ms early, and20160101_000000-0400.n083.wavhas the tone a little more than 100ms earlier than #82. #83-86 have the tone in the same place, and20160101_000000-0400.n087.wavhas the tone ~70ms earlier than #86.
Output File : '20160101_000000-0400.n081.wav'
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Comment : 'Processed by SoX'
sox DBUG trim: position 1 at 0
sox DBUG trim: position 2 at 308700
sox INFO sox: effects chain: input 44100Hz 2 channels (multi) 32 bits unknown length
sox INFO sox: effects chain: trim 44100Hz 2 channels (multi) 32 bits 00:00:07.00
sox INFO sox: effects chain: output 44100Hz 2 channels (multi) 32 bits 00:00:07.00
In:0.00% 00:09:27.01 [00:00:00.00] Out:25.0M [ | ] Clip:65.1k
sox DBUG wav: Finished writing Wave file, 2469600 data bytes 308700 samples
Input File : 'default' (coreaudio)
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Level adjust : 1 (linear gain)
sox DBUG wav: Writing Wave file: Microsoft PCM format, 2 channels, 44100 samp/sec
sox DBUG wav: 352800 byte/sec, 8 block align, 32 bits/samp
Output File : '20160101_000000-0400.n082.wav'
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Comment : 'Processed by SoX'
sox DBUG trim: position 1 at 0
sox DBUG trim: position 2 at 308700
sox INFO sox: effects chain: input 44100Hz 2 channels (multi) 32 bits unknown length
sox INFO sox: effects chain: trim 44100Hz 2 channels (multi) 32 bits 00:00:07.00
sox INFO sox: effects chain: output 44100Hz 2 channels (multi) 32 bits 00:00:07.00
In:0.00% 00:09:28.17 [00:00:00.00] Out:25.1M [ | ] Clip:65.1ksox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
In:0.00% 00:09:28.28 [00:00:00.00] Out:25.1M [ | ] Clip:65.1ksox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
In:0.00% 00:09:28.56 [00:00:00.00] Out:25.1M [ | ] Clip:65.1ksox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
In:0.00% 00:09:29.10 [00:00:00.00] Out:25.1M [!=====|=====!] Hd:0.0 Clip:66.8ksox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
In:0.00% 00:09:29.38 [00:00:00.00] Out:25.1M [ | ] Hd:0.0 Clip:66.8ksox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
In:0.00% 00:09:34.02 [00:00:00.00] Out:25.3M [ | ] Hd:2.7 Clip:66.8k
sox DBUG wav: Finished writing Wave file, 2469600 data bytes 308700 samples
Input File : 'default' (coreaudio)
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Level adjust : 1 (linear gain)
sox DBUG wav: Writing Wave file: Microsoft PCM format, 2 channels, 44100 samp/sec
sox DBUG wav: 352800 byte/sec, 8 block align, 32 bits/samp
Output File : '20160101_000000-0400.n083.wav'
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Comment : 'Processed by SoX'
sox DBUG trim: position 1 at 0
sox DBUG trim: position 2 at 308700
sox INFO sox: effects chain: input 44100Hz 2 channels (multi) 32 bits unknown length
sox INFO sox: effects chain: trim 44100Hz 2 channels (multi) 32 bits 00:00:07.00
sox INFO sox: effects chain: output 44100Hz 2 channels (multi) 32 bits 00:00:07.00
In:0.00% 00:09:41.01 [00:00:00.00] Out:25.6M [ | ] Clip:68.5k
sox DBUG wav: Finished writing Wave file, 2469600 data bytes 308700 samples
Input File : 'default' (coreaudio)
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Level adjust : 1 (linear gain)
sox DBUG wav: Writing Wave file: Microsoft PCM format, 2 channels, 44100 samp/sec
sox DBUG wav: 352800 byte/sec, 8 block align, 32 bits/samp
Output File : '20160101_000000-0400.n084.wav'
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Comment : 'Processed by SoX'
sox DBUG trim: position 1 at 0
sox DBUG trim: position 2 at 308700
sox INFO sox: effects chain: input 44100Hz 2 channels (multi) 32 bits unknown length
sox INFO sox: effects chain: trim 44100Hz 2 channels (multi) 32 bits 00:00:07.00
sox INFO sox: effects chain: output 44100Hz 2 channels (multi) 32 bits 00:00:07.00
In:0.00% 00:09:48.02 [00:00:00.00] Out:25.9M [ | ] Clip:69.4k
sox DBUG wav: Finished writing Wave file, 2469600 data bytes 308700 samples
Input File : 'default' (coreaudio)
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Level adjust : 1 (linear gain)
sox DBUG wav: Writing Wave file: Microsoft PCM format, 2 channels, 44100 samp/sec
sox DBUG wav: 352800 byte/sec, 8 block align, 32 bits/samp
Output File : '20160101_000000-0400.n085.wav'
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Comment : 'Processed by SoX'
sox DBUG trim: position 1 at 0
sox DBUG trim: position 2 at 308700
sox INFO sox: effects chain: input 44100Hz 2 channels (multi) 32 bits unknown length
sox INFO sox: effects chain: trim 44100Hz 2 channels (multi) 32 bits 00:00:07.00
sox INFO sox: effects chain: output 44100Hz 2 channels (multi) 32 bits 00:00:07.00
In:0.00% 00:09:55.01 [00:00:00.00] Out:26.2M [ | ] Clip:71.2k
sox DBUG wav: Finished writing Wave file, 2469600 data bytes 308700 samples
Input File : 'default' (coreaudio)
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Level adjust : 1 (linear gain)
sox DBUG wav: Writing Wave file: Microsoft PCM format, 2 channels, 44100 samp/sec
sox DBUG wav: 352800 byte/sec, 8 block align, 32 bits/samp
Output File : '20160101_000000-0400.n086.wav'
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Comment : 'Processed by SoX'
sox DBUG trim: position 1 at 0
sox DBUG trim: position 2 at 308700
sox INFO sox: effects chain: input 44100Hz 2 channels (multi) 32 bits unknown length
sox INFO sox: effects chain: trim 44100Hz 2 channels (multi) 32 bits 00:00:07.00
sox INFO sox: effects chain: output 44100Hz 2 channels (multi) 32 bits 00:00:07.00
In:0.00% 00:10:02.00 [00:00:00.00] Out:26.5M [ | ] Clip:73.0k
sox DBUG wav: Finished writing Wave file, 2469600 data bytes 308700 samples
Input File : 'default' (coreaudio)
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Level adjust : 1 (linear gain)
sox DBUG wav: Writing Wave file: Microsoft PCM format, 2 channels, 44100 samp/sec
sox DBUG wav: 352800 byte/sec, 8 block align, 32 bits/samp
Output File : '20160101_000000-0400.n087.wav'
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Comment : 'Processed by SoX'
sox DBUG trim: position 1 at 0
sox DBUG trim: position 2 at 308700
sox INFO sox: effects chain: input 44100Hz 2 channels (multi) 32 bits unknown length
sox INFO sox: effects chain: trim 44100Hz 2 channels (multi) 32 bits 00:00:07.00
sox INFO sox: effects chain: output 44100Hz 2 channels (multi) 32 bits 00:00:07.00
In:0.00% 00:10:02.49 [00:00:00.00] Out:26.6M [ | ] Clip:73.0ksox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
sox WARN coreaudio: coreaudio: unhandled buffer overrun. Data discarded.
In:0.00% 00:10:09.01 [00:00:00.00] Out:26.9M [ | ] Hd:4.3 Clip:74.8k
sox DBUG wav: Finished writing Wave file, 2469600 data bytes 308700 samples
Input File : 'default' (coreaudio)
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Level adjust : 1 (linear gain)
sox DBUG wav: Writing Wave file: Microsoft PCM format, 2 channels, 44100 samp/sec
sox DBUG wav: 352800 byte/sec, 8 block align, 32 bits/samp
Output File : '20160101_000000-0400.n088.wav'
Channels : 2
Sample Rate : 44100
Precision : 32-bit
Sample Encoding: 32-bit Signed Integer PCM
Endian Type : little
Reverse Nibbles: no
Reverse Bits : no
Comment : 'Processed by SoX'
sox DBUG trim: position 1 at 0
sox DBUG trim: position 2 at 308700
sox INFO sox: effects chain: input 44100Hz 2 channels (multi) 32 bits unknown length
sox INFO sox: effects chain: trim 44100Hz 2 channels (multi) 32 bits 00:00:07.00
sox INFO sox: effects chain: output 44100Hz 2 channels (multi) 32 bits 00:00:07.00
In:0.00% 00:10:16.00 [00:00:00.00] Out:27.2M [ ===|=== ] Clip:74.8k
sox DBUG wav: Finished writing Wave file, 2469600 data bytes 308700 samples
The most obvious red flag file is #82, so here are the stats:
$ sox 20160101_000000-0400.n082.wav -n stat
Samples read: 617400
Length (seconds): 7.000000
Scaled by: 2147483647.0
Maximum amplitude: 1.000000
Minimum amplitude: -1.000000
Midline amplitude: -0.000000
Mean norm: 0.011100
Mean amplitude: 0.000007
RMS amplitude: 0.081444
Maximum delta: 1.024212
Minimum delta: 0.000000
Mean delta: 0.001581
RMS delta: 0.019782
Rough frequency: 1704
Volume adjustment: 1.000
For comparison, here's #85
$ sox 20160101_000000-0400.n085.wav -n stat
Samples read: 617400
Length (seconds): 7.000000
Scaled by: 2147483647.0
Maximum amplitude: 1.000000
Minimum amplitude: -1.000000
Midline amplitude: -0.000000
Mean norm: 0.011643
Mean amplitude: 0.000006
RMS amplitude: 0.083079
Maximum delta: 0.992008
Minimum delta: 0.000000
Mean delta: 0.001879
RMS delta: 0.020434
Rough frequency: 1726
Volume adjustment: 1.000