Static or electronic noise with mic input on PC

I was trying to record a vocal track on my computer using Audacity, but kept hearing an odd chirping hiss in the background. I did some digging and found that for several years people have been having trouble with the Realtek ALC889 and related audio chipset and Linux. There are a variety of work-arounds, and none worked for me. I even booted into Windows 7 and heard the same electronic buzzing in the background. This led me to look at a hardware solution instead of a driver nuance.

My microphone is connected to a Mackie ProFX8 v2 mixer and then the board feeds out of the mains to the microphone plug on the front of my PC. Any wiggling of the connection going into the PC led to more pronounced electronic buzzing. That seems to be the weak link. I recalled that this mixer board has a USB interface also, so I hooked that up and disconnected the PC’s mic input. I checked in System, Preferences, Sound, Input and saw that the input device was now listed as “Analog Input PCM2903B Audio CODEC”.

I went into Audacity and looked on the input devices, and this was not shown. Hmmmm. I went ahead and left the input set to “default: Front Mic:0” and hit record. It worked, and with no background noise at all. This is great, because now I can have multiple mics and sound coming through the mixer board with reverb and pipe it all through the USB connection.

You may need to set levels using the alsamixer command.

Here are some things I have discovered about this setup. Mackie doesn’t really document the USB output very well at all. It can be an input or an output without any sort of switch, apparently. There is NO volume control for the USB output.

I’m using the following configuration:
Mic is on XLR 1. Gain is set to nearly full. Slider is set to U.

USB connection from board to computer USB
(NOTE: output from the USB port is not related to the MAIN slider at all, but to the mic gain and slider. MAIN slider controls output to the MAIN Out and to XLR out on the back, I think. USB Thru button has no effect on USB output, nor does the knob USB Input Level.)

The only way I can increase or decrease mic volume is via mic gain or slider. No other volume control seems to affect the USB output on this board.

Just for kicks I did try the Main Out with an unbalanced dual 1/4-inch to stereo 3.5mm to my computer’s mic input. I got so much noise in the background that it was useless.

I also recorded using the Main Out to a handheld Sony digital voice recorder ICD-AX412 and it sounded very good indeed.

This leads me to conclude that the computer audio hardware is at fault. (ASUS P6X58D Premium motherboard with built-in audio). I’ll have to look into an add-on card from Soundblaster or other.

 

UPDATE: March 11, 2017  I bought a “ground loop isolator” for $9 on Amazon and plugged that in between by mixer board and the computer. Poof! No more odd electronic buzzing in the back ground. This means that the ground points for the two outlets in my office are different, and that creates a “potential” and causes the buzzing. Easy fix for a very annoying problem. This is the one I purchased: Ziocom Ground Loop Noise Isolator.

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