I also had to look at the source occasionally too. I investigated this, mainly though the debug logs in /var/log/messages produced by PulseAudio after starting it with pulseaudio -start -log-target=syslog -log-level=4. When module-suspend-on-idle was enabled, there was the popping sound but when module-suspend-on-idle was disabled, there was no sound output. However, when I tried this approach, the work-around didn’t work. Daniel Bader describes this work-around and how to configure MPD, in a blog post. This is achieved by disabling the module-suspend-on-idle PulseAudio module, then configuring applications to use PulseAudio rather than ALSA. Until there’s a driver modification, the work-around suggested (other than using the HDMI sound output or an external USB sound card) is to run PulseAudio on top of ALSA and keep the driver active even when no sound is being output. When the PWM function is activated, there’s a jump in output voltage which results in the popping sound. This is because a PWM output of the BCM2835 CPU is being used, rather than a standard DAC. The problem manifests itself as a loud pop or click, just before sound is output and just after sound output is stopped. I’ve managed to work around this, so thought it might be helpful the share my experiences with others in the same situation. I’m working on a security-related project with the Raspberry Pi and have encountered an annoying problem with the on-board sound output.
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March 2023
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