I need an expert in audio electronics!

ToddAndChips

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Hi there folks!

I'll try to be as brief and detailed as I can with this post but I feel like it may take some explaining to cover everything...

In short, I need help removing a high pitched whine noise from my audio setup. It's all been wired up to my computer for a while and I've had to make do with the background buzzing for now but I'd really like to get it sorted so I can really nail higher quality audio recording.

This is the current setup I have, and it's ordered in terms of where the audio signal starts and ends while recording:

-----

Samson C03 condenser microphone (XLR)

- connected via phantom powered XLR cable to -

Behringer Xenyx 802 mixer (standard, no USB part)

- connected via 1/4" jack to jack cable to -

Behringer Composer Pro-XL MDX2600 compressor/gate rackmount unit

- connected via 1/4" jack to jack cable to -

Behringer Xenyz Q802USB mixer

- connected via USB cable to -

Desktop PC running Windows 7

- connected via optical audio cable to -

Behringer MS20 speakers

- connected via 1/4" jack to -

Turtle Beach X12 headset (USB powered, from the Desktop PC)

-----

I've done a lot of googling and researching on this matter but I'm not very experienced with electronics. I know a fair bit about audio systems but I'm not too informed regarding the signals carried from cable to cable, grounding loops, and so on.

The buzz is high pitched in nature, and noticeable if I'm doing anything with just one or two vocal tracks (like voice overs etc). I've uploaded audio samples of the buzz, I will explain the circumstances of each file shortly.

I've played around with turning bits of the setup on and off and rewiring certain things to see if I can pinpoint the source of the humming, and this is what I've noticed so far:

- The humming sound only occurs when the computer is actively using the USB mixer as an audio input - for example, if I open recording software like Cubase or Audacity, if I join a Skype call, or if I just open the Windows sound panel and switch to the recording tab, the noise starts. If nothing is using the USB mixer as an input device, there is no humming sound. If I disable the device on the sound panel (by clicking the highlighted option here: Gyazo - af1124573b226dd0b28c562b2db83a3f.png the sound disappears. This makes me think it has something to do with the USB cable carrying a voltage into the mixer that interferes with the signal, but that's just a speculation.
- The humming sound is audible through the monitors whenever the input channel on the USB mixer AND the main output channel are both turned up (providing I have the control room/phones output up). If I turn either the input channel OR the main output channel on the mixer down, the sound disappears from the monitor. It also disappears from the recording if I turn the channels down when I record, but obviously no signal will appear in the recording software.
- It doesn't make a difference whether I use channel 1 or channel 2 on either the first non-USB mixer, or the USB one. The same hum occurs with every combination.
- Turning the compressor off and recording alters the volume of the louder whine, but it is still present. I the turning off the compressor (which turns off the gate with it) just allows all the background noise through, which masks the whine with what sounds like white noise, but obviously that's not ideal either.
- There is another high pitched whistle sound that happens in every case, which is not as audible, but sounds somewhat like a steady howling gale. It's easier to notice when the compressor is off and the channels on the mixer are both down all the way, though it only appears in recordings - there is no sign of this sound through the monitors at all.

Plugging in my headset changes the behaviour of the whine entirely. I've tried wiring the USB mixer in several ways to avoid the sound being audible but nothing has worked yet. The headset is powered by USB (it's a turtle beach one, it's not ideal for this sort of thing but it might help point someone in the direction of the problem's source). The USB powering the headset is plugged into my computer (doesn't matter which port, the whine still occurs). The 1/4" jack for the headset's sound input is plugged into the speakers, which are connected to the computer via optical cable and to the USB mixer via either phono cables or a minijack cable (used for monitoring only). This is what I've noticed so far:

- When I plug the headphones into the 1/4" jack socket on the front of the speakers, there is a whine in ALL situations where the input device is active on the computer. Whether the compressor is on or off, and whether the input channel and main output channel on the USB mixer are up or down all the way, the whine is steady and at the same volume.
- Disabling the device in the sound panel (as I screenshotted earlier) removes the whine, as does ensuring no programs are actively using the USB mixer as an audio input device.


From the research I've tried to do online, the only thing I can come across that I feel makes any sense is related to grounding. I have a series of cables moving in the following way:

Gyazo - 90d5013d8b98f9307970c9c396ae7b3f.png

Could it be possible that I'd need to look at getting cables that don't carry any extra voltage with them? Whether it's USB cables of that sort (if they even exist...) or shielded 1/4" jack cables?

Maybe it's a completely different issue entirely?


Attached are 4 sound samples that I recorded on Cubase (with the headset unplugged so it was monitored through the speakers) from various scenarios, listed below:

1. Compressor on, mixer in and out channels up significantly
2. Compressor on, mixer in and out channels down all the way
3. Compressor off, mixer in and out channels up significantly
4. Compressor off, mixer in and out channels down all the way

This is my first post so I'm not sure how the attachments lay themselves out, though the titles of the attached files explain the setup I used while recording that particular clip. With any luck it'll give people an idea of what sort of interference we're dealing with.


I hope someone out there can shed some light on this situation....I know of several people aside from myself with varying setups but similar problems that would be extremely appreciative of a solution!

Many thanks for any help in advance :)


Todd


P.S. Let me know if I haven't explained anything properly or if you need more detailed information, and I'll update or add to the thread accordingly!
 

Attachments

  • Compressor ON MixerInput_Output ON.mp3
    79 KB · Views: 36
  • Compressor ON MixerInput_Output OFF.mp3
    79 KB · Views: 35
  • Compressor OFF MixerInput_Output ON.mp3
    79 KB · Views: 36
  • Compressor OFF MixerInput_Output OFF.mp3
    79 KB · Views: 37
If you have a laptop, try using that without the charger plugged in (ie on battery power), if that sorts it then you have some sort of bad voltage going through USB as you predicted. As it sounds like its a proper desktop you have, you could try a USB PCI-E card with the option for an external PSU which would allow the correct voltage on the USB. Or try something like the ifi iUSBPower or iPurifier? I think they have a money back guarantee but I aren't sure. The optical ouput should be ok until you connect to your headset which will cause the same issue as USB is involved!
 
+1 to TomScrut.
I found that a cheap Maplin universal PSU solved the problem, as it has a 2 pin mains connection with no functional earth. This was a £30 instant fix my noise on the audio line.
 
Also, why do you have 2 mixers? You could use the output from the compressor directly into the PC, or use a mixer with an insert facility. This will help with signal to noise ratio no end.
 

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