Question about Behringer UCA-202 audio interface

Hi guys

I’m using a Behringer UCA-202 audio interface for my desktop, which supplements recording of my podcast. I purchased it at the suggestion of someone on these forums. I have two sets of RCA audio cables in one - one cable going from the Output of the soundcard into a recording channel on my mixer, and then another cable going from the MAIN OUT of mixer into the Input of the soundcard.

The UCA-202 eliminated 95% of the issues I had with direct line-in recording. In the past, pure silence would record at 3dB, which would lead to a small but audible crack which you’d hear every time you’d start playing whatever you just recorded. The UCA-202, thankfully, records everything at 0dB.

The 5% of the issues that remain center around a small, pulsing hum that always ends up in my recordings. I’m assuming it’s coming from the innards of my computer - fans, monitor, etc. - but it’s annoying, and you can always hear it faintly in the background of my podcast. None of my listeners have picked up on it, nor have my co-hosts - its just something that I, as a nitpicker, want to remedy.

Would I be able to hook up a compressor unit to help eliminate this hum, or should I upgrade my audio interface to something a little more pricey?

Hi prolificwackoman,

I have very little knowledge about such issues but in an attempt to improve my recording system I have skimmed the manual for the Cakewalk (by Boland) UA-1G audio interface. Attached is a page that warns against loop connections. The description of your connection seems to match. Maybe the Behringer UCA-202 audio interface has the same restriction.

UA-1G-warning against feedback loop.jpg

If you are recording on a laptop computer it may be necessary to run on batteries to eliminate background hums. The power supplies on PC laptops are notorious for creating electrical noise. If the power supply is the cause, then more expensive sound cards are also likely to suffer from the same problem.

That problem actually occurs if I flip the “MONITOR” switch on. If I pot up the slider for the channel on my mixer that is recording the audio coming out of my computer, the horrendous feedback occurs at around -30dB.

I fear it might be the power source, if anything, that is causing this pulsing hum. I’m going to experiment with switching cables and inputs around, and I’m awaiting the arrival of a compression unit on backorder, so maybe I can add a gate to cancel the hum out.

For reference, you can faintly hear the hum in my podcast. (WARNING: Vulgarity, and lots of it.) If you do listen, wait for the music bed to stop and listen to the gaps of silence.

That sounds like a quite different problem - it sounds like you have inadvertently created a “feedback loop”. Could you describe in detail your set-up, including how everything is wired up and what settings you have. Make and model of the equipment will help, and if possible, links to the relevant on-line manuals.

My set up is as follows:

My UCA-202 is hooked up to a USB port in the back of my PC. I have a stereo cable running the from the OUTPUT of the UCA-202, going into a recording channel on my mixer (so, effectively, all sound played from my computer goes into my mixer.) I have another stereo cable going from the MAIN OUT of the mixer into the INPUT of the UCA-202, so anything played from my computer can be recorded directly into said computer.

I have a feeling this pulsing hum is a result of the computer’s processors, the sounds of which are traveling through the USB cable into the UCA-202. I’ve experimented a bit - I took the stereo cable that was hooked up through the OUTPUT of the UCA-202 and instead hooked it directly into the headphone jack on my PC, and ran it into the recording channel of my mixer. The gain had no only increased by doing this, but the hum was more prevalent, leading me to believe that it might be the innards of my PC causing interference.

Do you think purchasing a Hum Eliminator might solve my issue?

If the signal coming OUT of the UCA-202 into your mixer is allowed to pass out from the mixer back into the INPUT of the UCA-202 then you have a potential feedback loop. This is almost certainly the cause of the “horrendous feedback” that you experienced.

Not impossible, but not very likely.

If the computer is a laptop then as said before laptop power supplies are notorious for creating noise. I don’t recall you specifically saying, but I presume your computer is a full size machine and not a laptop?

I would look at using a “Hum Eliminator” as a last ditch measure. Hum Eliminators do not “cure” the problem, at best they remove the “symptoms” of the problem. They also have a slightly detrimental effect on the sound quality due to their limited and non-linear frequency response.

Here’s a test to ensure that feedback through the mixer is not contributing to the problem.

Connect the USB of the UCA-202 to your computer.
Connect the MAIN OUT of the mixer into the INPUT of the UCA-202
DO NOT connect the OUTPUT of the UCA-202.
Record something.

Now disconnect the MAIN OUT of the mixer from the INPUT of the UCA-202
Connect the OUTPUT of the UCA-202 to the mixer.
Play back your recording.

Is that better/worse/no different from before?

Your assumption is correct, I am using a desktop.

I did what you suggested, and I uploaded my recordings to my server. The first is the recording I took while the cable was disconnected - the second is the recording with both cables in. About 9 seconds into both recordings, I set some amplification so you can hear exactly what the humming sounds like.

IMO, it sounded a lot worse with the cables unplugged.

Also, please let me know if you hear a noticeable “crack” when each file starts and ends - I’m hearing a crack on my end that wasn’t present until recently.

I see (hear) what you mean. The noise is not hugely loud, but enough to be an annoyance.

I agree that it sounds like electrical interference, though not necessarily from the innards of you computer. Do you have overhead power-lines or electric railways, or electricity substations, or anything else of that type close to your house that could account for it? If you do then you may get some improvement by using higher quality audio leads. Also check round the house for potential noise sources. Electric motors (fridges, freezers, air conditioning, …), fluorescent lights and lights with dimmer switches are favourite culprits. If practical to do so, as a test, go round your house and switch off everything electrical except for the computer and mixer.

Does the level of the noise change as you increase the channel gain on the mixer input? If you mute everything on the mixer and turn down all the sliders and gain knobs, do you still get the noise and is it about at the same level? If so, then the noise can be minimised by ensuring that the pre-fade level for the input channel is set reasonably high (metering the pre-fade level should go up to the top of the green and just into the yellow on mixer), and then setting the whole mix (output) level from the mixer reasonably high (but watch out for overloading the UCA-202 - they cannot handle particularly high signal levels).

No I don’t notice a “crack” when each file starts and ends. I suspect that is just the audio stream “switching on” when playback starts (and then off again when it stops). I presume that it is a fairly low level sound? Does it occur even with a totally silent track? (try opening a new project and generate 30 seconds of silence, then play it back).
The “crack” is certainly not present in the actual recorded waveform so as long as it is only quiet I expect that it is safe to ignore.

An update - first, that “crack” sound was 100% on my end. I’m glad you couldn’t hear it. I asked because, before I got the UCA-202 and utilized direct line-in recording, that crack sound was prevalent, as everything recorded at just a tad higher than 0db.

Second, I have temporarily solved the hum issue, for the most part. I plugged the UCA-202 into one of the USB ports on the front of my PC and set all of the equalization for the channel that is recording the output from the computer to 0. The hum is still present, but only if you crank the channels on the mixer all the way up, as well as the studio monitors.

I’m recording a new podcast tonight, so I will let you know if the hum returns at any point.

Don’t forget that mobile phones (cell phones), transportable domestic phones and fluorescent lights can all cause or add to hum - so it’s worth eliminating all that when recording.

Glad you’re getting a better result.