How do I make a machine “blank screen” for a period of time (as a penalty) if certain noise levels are reached?

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My kids (4 and 5) yell a lot when playing games on the computer. I found an effective cure for this. When I hear loud noises, I ssh into the game computer and do:

chvt 3;  sleep 15;  chvt 7

This will turn off the screen for 15 seconds on Linux. I’ve told them that the computer doesn’t like loud noises. They totally believe this and beg the computer for forgiveness. They became much quieter, but not to the level that I would be happy, and so I need to continue this educational process. However, I am not always around to do this manually.

Is it possible to automate this? A microphone is attached to the box. If the level of loudness passes some threshold then I want to run a command.

Answer

Use sox from SoX to analyze a short audio sample:

sox -t .wav "|arecord -d 2" -n stat

With -t .wav we specify we process the wav type, "|arecord -d 2" executes the arecord program for two seconds, -n outputs to the null file and with stat we specify we want statistics.

The output of this command, on my system with some background speech, is:

Recording WAVE 'stdin' : Unsigned 8 bit, Rate 8000 Hz, Mono
Samples read:             16000
Length (seconds):      2.000000
Scaled by:         2147483647.0
Maximum amplitude:     0.312500
Minimum amplitude:    -0.421875
Midline amplitude:    -0.054688
Mean    norm:          0.046831
Mean    amplitude:    -0.000044
RMS     amplitude:     0.068383
Maximum delta:         0.414063
Minimum delta:         0.000000
Mean    delta:         0.021912
RMS     delta:         0.036752
Rough   frequency:          684
Volume adjustment:        2.370

The maximum amplitude can then be extracted via:

grep -e "RMS.*amplitude" | tr -d ' ' | cut -d ':' -f 2

We grep for the line we want, use tr to trim away the space characters and then cut it by the : character and take the second part which gives us 0.068383 in this example. As suggested by comments, RMS is a better measure of energy than maximum amplitude.

You can finally use bc on the result to compare floating-point values from the command-line:

if (( $(echo "$value > $threshold" | bc -l) )) ; # ...

If you build a loop (see Bash examples) that calls sleep for 1 minute, tests the volume, and then repeats, you can leave it running in the background. The last step is to add it to the init scripts or service files (depending on your OS / distro), such that you do not even have to launch it manually.

Attribution
Source : Link , Question Author : Leonid Volnitsky , Answer Author : tucuxi

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