DAC+ADC pro annoying crack on output when starting to record from input


I am using a bunch of raspis with various Hifiberry Boards on them. My architecture is to use plain Raspbian and some Ansible Roles to configure the audio setup. We just use alsa and everything is set to use a sample rate 44100 (CD format).

My main raspi is connected twice to my main amp:
* The DAC output goes to the "Tuner" Cinch Input of the amp, this is selected as output to the loudspeakers.
* The ADC Input is connected to the "Rec Out" of my amp. The amp has a separate REC selector (this is important to make my use case happen).

In order to listen to my vinyl records in all rooms, the audio path on my main raspi is as follows:

* The record player plays a record.
* The rec out selector on the amp is on phono
* The vinyl sound exits the amp and enters the ADC
* I have a permanent `acable` ( a `arec | aplay` pipe) process copying the dsnoop input from the ADC to the dmix input of a virtual alsa audio card (snd_aloop).
* The snapserver takes the audio from the snd_aloop output dsnoop device and feeds it (FLAC/CD-format) to all snapclients on the network, including the local one.
* The local snapclient plays the audio to the ADC dmix output
* The audio signal goes to the "tuner" input cinch connectors
* and is played on the local loudspeakers (with a local delay of about 1 sec, but in sync with all other rooms).

When I stop the `arec` on the ADC-dsnoop device, nothing happens (except that I have no analog sound any more).

But when I start the `arec`, a very loud crack is heard on my loudspeakers. The crack has neither delay nor can it be heard in the other rooms. So I am sure that the crack is NOT transported via snapcast, but there must be hardware (or driver?) issue.

I own a DAC+ADC (without pro) too, and I believe it has exactly the same issue.


Please sign in to leave a comment.