Cannot set Logitech quickcam pro4000 microphone level

[yannouch]

Hi

I've got my logitech quickcam pro4000 working, both image & sound (integrated microphone)

I use alsa snd-usb-audio for the integrated microphone, but cannot set the level, it's blocked at 100%, and thus I have larsen.

any idea why I can't set the recording level ?

Thanks