No capture controls on USB soundcard (Creative SB X-Fi HD)

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https://bbs.archlinux.org – I have a Creative SoundBlaster X-Fi HD USB sound card. Seems to work out of the box when I plug it in, using snd_usb_audio module. When I start alsamixer, in the Playback view it shows two controls: PCM, and PCM Capture Source which allows me to switch between Mic, Line and Phono, three different inputs on the card. In the Capture view, it says "This sound device does not have any capture controls". I want to use it for recording. I have a microphone plugged in, select Mic as the PCM capture source. In Audacity, I cannot control the input volume (it tells me to use the system mixer). (HowTos)