SOLVED: ASUS Xonar U7-can't capture with this USB sound card

[gordonp]

Hi, fellow Gentoo'ers -

I will be deeply grateful for all help in getting my USB sound device to work with input-capture.

PROBLEM:
I cannot get input-capture (microphone) to work with my Xonar U7 device This Xonar U7 ~does~ work for output/playback. My motherboard's built-in sound does work for both capture and output/playback. As a result, this "feels" like a configuration, driver, or other software-related issue. I would appreciate some troubleshooting steps to help diagnose and fix this. Thanks in advance!!

DESIRED USAGE:
I am a ham-radio operator, and I enjoy using Gentoo + fldigi (an application) to communicate via data-over-radio. I have had this working for many years, but a recent computer-upgrade led me to purchase an ASUS Xonar U7 sound-"card", rather than continue with my previous PCI SoundBlaster. I use this secondary sound card to process received radio-tones into 1's and 0's via sound-card mic-input, to decode radio-data; conversely, I also use this secondary sound card output to generate high-quality tones which I inject into my radio's microphone-socket, to transmit my own 1's and 0's. Good signal-to-noise, low jitter, bit-depth and sample-rate affect quality, and the U7 reads nicely for this purpose.

The primary sound card (built onto the motherboard - an ASUS Rampage V Extreme) is used for the usual sound stuff: multimedia playback, voice-chat, system-notifications, etc. That is, less-demanding stuff.

• I want to dedicate my motherboard sound to voice-chat, and general system uses.
  
• I want to dedicate my fldigi and ham uses to the Xonar U7 outboard USB sound.

WHAT WORKS:

• I can use fldigi + motherboard-sound, and everything works. Essentially this verifies my hardware, radio connections, and signal levels, along with verifying the USE-flags and configuration-settings for fldigi. The connections and USE-flags also have a long history of working properly, before my system upgrades.
  
• I can use fldigi for TRANSMIT ONLY with the Xonar U7.
  
• With alsamixer, I can see the various, usual Playback channels. And I can see two Capture channels, which the space-bar can turn on or off.

WHAT DOESN'T WORK:

• I cannot get my ASUS Xonar U7 USB sound-device to "capture". I supply live microphone input, but nothing happens.
  
• pavucontrol, and gnome-control-center -> Sound both show a complete lack of any inputs for the U7
  
• I have created/edited /etc/modprobe.d/alsa-base.conf to ignore control errors, but it makes no difference with or without:

[gordonp]

I found my answer here:

https://wiki.archlinux.org/index.php/PulseAudio/Troubleshooting#Microphone_not_detected_by_PulseAudio

The summary:

I edited /etc/pulse/default.pa to add the line: