End sox recording once silence is detected

Question

I'm writing a script that uses sox to record me talking. Now I need sox to wait until it detects sound before it begins recording, and I do have that figured out. But I also need sox to exit once there has been silence for at least 3 seconds. As it is now, I have to manually kill sox once I finish talking, otherwise sox just waits again until I talk some more, appending to the output file (That's not what I want). Here is the command for recording I am using now:

rec /tmp/recording.flac rate 32k silence 1 0.1 3% -1 3.0 3%

Again, just to be clear, Sox should wait until I start talking, and then record until I stop talking, then the sox program should quit.

Answer 1

Remove the negative sign from your original command:

rec /tmp/recording.flac rate 32k silence 1 0.1 3% 1 3.0 3%

When the "below count" is negative, the silence command will trim all silences from the middle of the file. When it's positive, it trims silence from the end of the file.

Answer 2

I found a kind of shaky way that sort of solves this problem.

I noticed that when silence is detected, sox naturally won't append anything more to the file until it hears more sound. So I decided I could try and take advantage of this fact.

First of all, I start up sox's sound recorder in the background:

rec /tmp/recording.flac rate 32k silence 1 0.1 3% -1 3.0 3% &

Next I get the PID of the recording process with: p=$!

Then I give the recording process a second to finish starting up, and then wait until the file starts to grow.

sleep 1
until [ "$var1" != "$var2" ]; do
    var1=`du "/tmp/recording.flac"`
    sleep 1
    var2=`du "/tmp/recording.flac"`
done

After this loop breaks, that means that sound has been detected. So now I create another loop to wait until data stops being appended to the file (This will happen once sox detects silence again).

echo "Sound Detected"
until [ "$var1" == "$var2" ]; do
    var1=`du "/tmp/recording.flac"`
    sleep 0.5
    var2=`du "/tmp/recording.flac"`
done

Now I just need to quit rec:

echo "Silence Detected"
kill $p

And that's it. Here is the completed script:

rec /tmp/recording.flac rate 32k silence 1 0.1 3% -1 3.0 3% &
p=$!
sleep 1
until [ "$var1" != "$var2" ]; do
    var1=`du "/tmp/recording.flac"`
    sleep 1
    var2=`du "/tmp/recording.flac"`
done
echo "Sound Detected"
until [ "$var1" == "$var2" ]; do
    var1=`du "/tmp/recording.flac"`
    sleep 0.5
    var2=`du "/tmp/recording.flac"`
done
echo "Silence Detected"
kill $p

Now I would prefer a better, more stable way to do this, but this will have to work for now.

Answer 3

I tweaked the above ideas some more. It records forever, records all noise until (roughly) a second of silence is encountered. Then:

• Ensures two subdirectories are created
• Calculates two spectrographs of the recording - one before normalisation, and one after, and writes to datestamped folders.
• Writes the normalised one to a file to a datestamped folder.
• Plays the normalised file back, with two chirp .ogg files (back through voice operated CB Radio)

(Makes for a very handly little UHF / 2 metre echo repeater)

#!/bin/bash
while true; do
  rec buffer.ogg silence 1 0.1 5% 1 1.0 5%
  DATE=`date +%Y%m%d%H%M%S`
  DPATH=`date +%Y/%m/%d/`
  mkdir -p ./spectro/$DPATH
  mkdir -p ./voice/$DPATH
  echo Renaming buffer file to $DATE
  sox buffer.ogg -n spectrogram -x 300 -y 200 -z 100 -t $DATE.ogg -o ./spectro/$DPATH/$DATE.png
  sox buffer.ogg normbuffer.ogg gain -n -2
  sox normbuffer.ogg -n spectrogram -x 300 -y 200 -z 100 -t $DATE.norm.ogg -o ./spectro/$DPATH/$DATE.norm.png
  mv normbuffer.ogg ./voice/$DPATH/$DATE.ogg
  play pre.ogg ./voice/$DPATH/$DATE.ogg post.ogg 
done

Answer 4

This listens forever, records only the last sounds until it hears one second of silence, then writes the file, timestamps it, and restarts:

#!/bin/bash
/usr/bin/sox -t alsa default /home/default/working/recording.wav silence 1 0.1 5% 1 1.0 5%
DATE=$(date +%Y%m%d%H%M%S)
mv /home/default/working/recording.wav /home/default/waiting/$DATE.recording.wav
/home/default/startrecord.sh