VW e-Golf & ID.4 Pro S
It means the audio output from the head-unit is compressed to reduce the high and low-frequency outputs. Think of MP3 music, the audio is compressed which results in a loss of up 40% of the depth of sound. You miss an amazing amount of detail if you are able to listen to the original music source with high quality audio kit. Automakers do this is to avoid warranty claims from speaker damage when folks play their music at high volume. Most folks don't care or even notice unless you are really into audio or an audiophile.