Input clipping happening at -8.0 dBFS

I’ve bought Behringer Uphoria UMC 404HD.
It works out of the box on my Ubuntu 21.10.
I’m using Ardour 6.9.0 with Jack.

I plugged in a Roland RD800 stage piano to Input 1 (L) and 2 (R).
The sound of the piano gets correctly to Ardour and the meters react properly.

However I noticed one thing is probably not quite right.
When I play loudly, the clipping LEDs on the interface light red and the sound gets distorted, but the input meters in Ardour mixer peak at exactly -8.0 dBFS and I can’t make them go up to 0 dBFS. I thought clippin should happen when the meters go up (or above) 0 dBFS. The meters are set to meter the input.

I’m very new to Ardour - can somebody direct me how to fix metering? Or can it be something else that’s wrong?

edit: I tested the exact same thing happens on Inputs 3 and 4.

Does the device have a software controlled mixer?

In a terminal run alsamixer, then <F6> to select the device and <F5> to show all controls.

Perhaps the analog signal clips, but it is then attenuated after A/D conversion?

Thank you, that was it!

After setting those alsamixer faders to 100%, the input meter in Ardour goes up to 0 dBFS, but can’t exceed that. Is it expected behavior? However, the meter scale ends at +6 dBFS. Why is that and when can it be useful? What is the purpose of that?

Yes. FS = Full Scale. 0 dBFS means max possible analog signal.

Ardour’s Fader can add up to +6dB of gain. So if you measure post-fader that can be handy.

You can however right-click on the meter and change it to align at 0 dBFS at the top. see also – or change the default for new sessions in Preferences > Metering.

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