Source (2017/09) https://www.hifiberry.com/build/documentation/libreelec-installation-and-configuration/

In some cases the volume mixer level is set to 100% by default. This can result in distortions of the music output. Therefore you should set this to around 80%. Login via SSH and use the following command:

amixer -c 0 set Digital 80%

You may want to experiment with the percentage volume in order to tune it to your desired preference.

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