Playing a Sound at a Specific Volume Every 15 Minutes: A Comprehensive Guide

This guide addresses the challenge of playing a sound file at a precise volume level at regular intervals, irrespective of the system’s overall volume settings, using a Linux system (specifically Pop!_OS 22.04 in this example) and a USB audio interface (like the Focusrite Scarlett 2i2). We will explore methods to achieve this without intrusive pop-up windows, ensuring background operation. The context is maintaining active speaker status to prevent sleep mode activation in KRK Rokit 5 monitors.

Understanding the Problem: System Volume Dependency

The issue stems from the play command’s reliance on the system’s master volume. Using the -v option for volume control creates a relative adjustment, thus requiring a compromise between system volume and application volume. To circumvent this, we need a solution that directly sets the output level, bypassing system volume settings.

Solutions Using Different Tools and Techniques

Several approaches can achieve precise volume control independent of the system volume, ensuring a consistent playback level every 15 minutes without user intervention.

Method 1: Utilizing pactl for Precise Volume Control

PulseAudio (pactl) offers granular control over audio output, allowing precise volume adjustments at the application level. This bypasses system-wide volume management.

Setting up a custom script:

This method involves creating a shell script that leverages pactl to set the volume to a specific percentage before playing the audio file. The script then plays the 10Hz.wav file, using the pactl command. It then returns to its previous level and returns.

#!/bin/bash

# Get the current sink volume.
current_volume=$(pactl get-sink-volume @DEFAULT_SINK | awk -F'[' '{print $2}' | awk -F'%' '{print $1}')

# Set the sink volume to 100%.
pactl set-sink-volume @DEFAULT_SINK 100%

# Play the audio file.
play -v 1.0 /home/USER/rmas/10Hz.wav

#Restore the volume to its original state.
pactl set-sink-volume @DEFAULT_SINK $current_volume%

exit 0

Save this script (e.g., as play_audio.sh) and make it executable (chmod +x play_audio.sh). The @DEFAULT_SINK may require adjusting to point to your correct audio device, particularly with multiple audio devices present. Remember to replace /home/USER/rmas/10Hz.wav with the actual path to your file.

Scheduling with Cron:

Schedule this script to run every 15 minutes using crontab:

*/15 * * * * /path/to/play_audio.sh

Replace /path/to/ with the actual path to your play_audio.sh script. This ensures background execution without user interaction. Error handling within the script is essential for robustness; consider adding error checks and logging to ensure reliable operation.

Method 2: Employing ffmpeg for Advanced Audio Manipulation

FFmpeg provides extensive audio processing capabilities. We can use it to create a new audio file with the exact volume level needed. This removes the need for runtime volume adjustments, simplifying the process.

Pre-processing the Audio File:

This involves using ffmpeg to create a new 10Hz audio file with the desired volume level embedded. The original file will be untouched.

ffmpeg -i /home/USER/rmas/10Hz.wav -filter:a "volume=1" /home/USER/rmas/10Hz_100percent.wav

This command creates /home/USER/rmas/10Hz_100percent.wav, ensuring consistent 100% volume independent of system settings. The -filter:a "volume=1" applies the volume filter. Modify 1 for different percentage of volume (e.g., 0.5 for 50%).

Simplified Cron Job:

Once the pre-processed audio file is created, the cron job becomes much simpler:

*/15 * * * * play /home/USER/rmas/10Hz_100percent.wav

This directly plays the file at the predetermined volume. No volume adjustments are needed during runtime. This approach significantly reduces the script’s complexity and potential error points.

Method 3: A Python-based solution for more flexibility

Python, with its extensive libraries, offers increased control and flexibility. We can leverage the pyaudio library for precise audio output management.

Python Script Development: 

import pyaudio
import wave
import time

CHUNK = 1024
RATE = 44100  # Adjust according to your wave file's sample rate
VOLUME = 1.0  # 0.0 to 1.0 for 0 to 100% volume.

wave_file = "/home/USER/rmas/10Hz.wav"

p = pyaudio.PyAudio()

wf = wave.open(wave_file, 'rb')

stream = p.open(format=p.get_format_from_width(wf.getsampwidth()),
                channels=wf.getnchannels(),
                rate=RATE,
                output=True)

while True:
    data = wf.readframes(CHUNK)
    if not data:
        break
    stream.write(data)

stream.stop_stream()
stream.close()

wf.close()

p.terminate()

This script plays the file using pyaudio, allowing direct volume control. You can adjust the VOLUME variable to your needs. You would adapt the crontab entry to this python script. This approach enhances customization and allows for more complex audio management functionalities if needed.

Troubleshooting and Considerations

  • Audio Device Selection: Verify that play, pactl or pyaudio are targeting the correct audio output device (your Scarlett 2i2). Use appropriate commands to confirm the correct device is selected before attempting to play the file.
  • Wave File Format: Ensure your 10Hz.wav file is in a compatible format. Use sox to convert it if necessary.
  • Error Handling: Include robust error handling in your scripts (check for file existence, audio device availability, etc.). This ensures the reliability of your automated process.
  • Resource Usage: Monitor system resource usage, especially for the Python solution, to prevent potential performance issues. Adjust the CHUNK size accordingly if needed.

Choosing the Best Approach:

The best method depends on your comfort level with scripting and the level of control needed. The pactl method offers a balance of simplicity and control. The ffmpeg method is ideal for a simple, efficient, pre-processed solution. The Python approach provides the most flexibility for advanced control and error handling. Select the method that aligns best with your skill set and requirements. Remember to adapt the paths to match your file system. Proper testing is essential to ensure your selected method functions correctly in your environment.