Monitoring the microphone level with a command line tool in Linux

This solution will avoid writing repeatedly to disk, and even though it in worst case takes a second instead of the desired less than half a second, I found it to be fast enough after trying it. So, here are the two scripts I use:

./detect:

while true; do
    arecord -d 1 /dev/shm/tmp_rec.wav ; sox -t .wav /dev/shm/tmp_rec.wav -n stat 2>\
    &1 | grep "Maximum amplitude" | cut -d ':' -f 2 | ./check.py
    if [ $? -eq 0 ] ; then
         amixer set Master 0
    else
         amixer set Master 80
    fi
done

./check.py:

#!/usr/bin/env python
import sys

number = 0.0
thing="NO"

line = sys.stdin.readline()
thing = line.strip()
number = float(thing)

if number < 0.15:
    raise Exception,"Below threshold"

Hardly elegant, but it works.

Note: If you want a more gradual thing, add something like this:

   for i in `seq 0 80 | tac`; do
      amixer set Master $i
   done

for muting and

   for i in `seq 0 80`; do
      amixer set Master $i
   done

for unmuting.

Just version without python script and TALKING_PERIOD, that sets up how many seconds will sound be on DOWN_SOUND_PERC level, then goes to UP_SOUND_PERC level.

#!/bin/bash
    
TALKING_PERIOD=16
UP_SOUND_PERC=65
DOWN_SOUND_PERC=45
counter=0

while true; do
    echo "counter: " $counter
    if [ "$counter" -eq 0 ]; then
        nmb=$(arecord -d 1 /dev/shm/tmp_rec.wav ; sox -t .wav /dev/shm/tmp_rec.wav -n stat 2>&1 | grep "Maximum amplitude" | cut -d ':' -f 2)

        echo "nmb: " $nmb

        if (( $(echo "$nmb > 0.3" |bc -l) )); then
            echo "ticho"
            amixer -D pulse sset Master 45%
            counter=$TALKING_PERIOD
        else
            echo "hlasno"
            amixer -D pulse sset Master 65%
        fi
    fi

    if [[ $counter -gt 0 ]]; then
        ((counter--))
    fi

    sleep 1

done