Low volume for click sounds

We found a strange sound effect with WinEC7 on an iMX6S board. It seems the volume and characteristics of a click sound is dependent on the speed of clicking. When playing multiple click sounds quickly after each other the sound seems to work well. When waiting for more than a second between the sounds it is much lower in volume. We can easily reproduce this over Control Panel → Volume & Sounds by playing a click sound (e.g. menusel.wav). The registry settings are default (unchanged). We measured directly at the output pin of the CPU (pin 17: HEADPHONE_R) and could see the lower signal there.
Is that a known behavior?

Dear @widtmann

The Colibri iMX7 implements the SGTL5000 audio codec. This codec has a hardware fade-in feature, which increases the volume slowly while powering up, to avoid any pop sound.
The menusel.wav is a very short sample, which is finished before the volume reaches the full level. If you play it multiple times, the codec is not powered-down between the samples, and the volume hence remains active at full level.

You can disable the fade-in by adding the following registry setting:

Reg0x0e = dword:0x03000000

This will clear the bits VOL_RAMP_EN and VOL_EXPO_RAMP in the register CHIP_ADCDAC_CTRL.

I just found that this registry feature is documented for PXA and Tegra (Audio Driver Registry Settings), but not for iMX6. I will make sure the documentation is updated accordingly.

Regards, Andy

This registry setting fixes our issue. Thank you very much!