Logitech c920 microphone not working in Ubuntu 18.04

Question

Recently my Logitech c920 webcam microphone stopped working on my ubuntu 18.04. Microphone (input) recognized by system but not catching any sound. Skype and Cheese recognizing input but not catching any sound. Not hardware issue. When re-booting to Windows 10 everything working well. I am running out of ideas.

~$ arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: CA0132 Analog [CA0132 Analog]
  Subdevices: 0/1
  Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 2: CA0132 What U Hear [CA0132 What U Hear]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: C920 [HD Pro Webcam C920], device 0: USB Audio [USB Audio]
  Subdevices: 0/1
  Subdevice #0: subdevice #0

~$ cat /proc/asound/cards
 0 [PCH            ]: HDA-Intel - HDA Intel PCH
                      HDA Intel PCH at 0xed540000 irq 144
 1 [NVidia         ]: HDA-Intel - HDA NVidia
                      HDA NVidia at 0xed080000 irq 18
 2 [C920           ]: USB-Audio - HD Pro Webcam C920
                      HD Pro Webcam C920 at usb-0000:00:14.0-4, high speed

Alsamixer output:

 ~$ alsamixer 
┌────────────────────────────── AlsaMixer v1.1.3 ──────────────────────────────┐
│ Card: HD Pro Webcam C920                             F1:  Help               │
│ Chip: USB Mixer                                      F2:  System information │
│ View: F3: Playback  F4:[Capture] F5: All             F6:  Select sound card  │
│ Item: Mic [dB gain: 50.00]                           Esc: Exit               │
│                                                                              │
│                                     ┌──┐                                     │
│                                     │▒▒│                                     │
│                                     │▒▒│                                     │
│                                     │▒▒│                                     │
│                                     │▒▒│                                     │
│                                     │▒▒│                                     │
│                                     │▒▒│                                     │
│                                     │▒▒│                                     │
│                                     │▒▒│                                     │
│                                     │▒▒│                                     │
│                                     │▒▒│                                     │
│                                     │▒▒│                                     │
│                                    L└──┘R                                    │
│                                   CAPTURE                                    │
│                                     100                                      │
│                                  <  Mic   >                                  │
│                                                                              │
└──────────────────────────────────────────────────────────────────────────────┘

~$ lsusb
Bus 002 Device 004: ID 05e3:0732 Genesys Logic, Inc. All-in-One Cardreader
Bus 002 Device 005: ID 0781:5580 SanDisk Corp. SDCZ80 Flash Drive
Bus 002 Device 003: ID 2109:0812 VIA Labs, Inc. VL812 Hub
Bus 002 Device 002: ID 045b:0210 Hitachi, Ltd 
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 006: ID 20f4:805b TRENDnet 
Bus 001 Device 005: ID 2109:2812 VIA Labs, Inc. VL812 Hub
Bus 001 Device 004: ID 046d:082d Logitech, Inc. HD Pro Webcam C920
Bus 001 Device 003: ID 046d:c52b Logitech, Inc. Unifying Receiver
Bus 001 Device 007: ID 1b1c:0c03 Corsair 
Bus 001 Device 002: ID 045b:0209 Hitachi, Ltd 
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Answer 1

I had this problem recently on Elementary OS 5 (Juno).

The solution was activating a kernel module that shouldn't be inactive in the first place:

modprobe snd_usb_audio

Now, for some reason Digital S/PDIF input still dowsn't work but the regular Microphone input does.

Hope it helps.

Answer 2

I fixed this by changing /etc/pulse/daemon.conf default-sample-rate = 48000

Although this was the alternate-sample-rate, used to avoid resampling, I believe that's only used if there's not something already doing some audio at default-sample-rate, which I guess would explain why my C922 audio sometimes worked and sometimes didn't, and had stopped working altogether until I made this change. Not really a satisfactory explanation but it fixed it for me.