Noise Problems

[finotti]

I've been having some noise problems recently. Although it seems that it's been fixed, I have thought that before and it keeps coming back.

My setup is the following: guitar connected to a passive direct box (Radial’s ProDI). From the output it goes to the first input of the interface (2nd generation Focusrite 2i2) and from the through it goes to a Line 6 HX Stomp (also connected to the PC with a USB cable) and from its output to the second input of the interface.

The HX Stomp can be used as interface, but most often it is just used to provide processing before the second input of the 2i2.

I was having really unbearable noise problems and was trying to figure out the problem. I was playing though with the HX Stomp off (although it had a lot of noise with it on as well) and recording just the direct signal from input 1.

I tried changing cables, moving USB ports, changing power supply outlets, hitting ground lift on the direct box, etc. Nothing worked.

Then, I disconnected the audio cable from the HX Stomp from the second input and the noise stopped!

Now, a few strange things happened after that. I hit the ground lift in the direct box and the 2i2 disconnected/turned off. I had to disconnect its USB cable and reconnect a few times for it turn back on. I though this was quite strange.

When it was on and I connected the HX Stomp back, I was expecting the terrible noise to come back, but it did not.... (At least, not then. I haven't tried more than a couple of times so far.)

Now, I do need to have both inputs (direct and HX Stomp) connected at times, to record the DI and the processed sound, so it is important that I can get rid of noise for good.

Any suggestions on how to figure out the problem?

I've seen this iFi iDefender+ USB Audio Ground Loop Eliminator being recommended, but it is not too cheap. I'd gladly buy it if it is a solution, but I'd prefer to know if ground loops is really the problem before spending the money on it. (And I just noticed that it does not provide power, so I'd need to buy their power supply, another $69!, to provide power to the 2i2.)

[tseaver]

@finotti I'm not familiar with the particular hardware you are using, but the symptoms definitely sound like a ground loop: the HX Stomp is sending signal to channel two of the Focusrite interface which is "ungrounded" compared to the signal from the DI to channel one.

Can you try toggling the "Lift" switch on the DI box? On the (much cheaper) DIs I use, that would make a huge difference.

[kamiluni]

@finotti please describe the kind of noise or record it and attach to a post. There are many causes for the noise, but the "kind" of noise can address the root cause.

[bluzee]

Sounds like ground loop. Not sure if it would make a difference but if I had to wire this configuration I would plug guitar into stomp box, use effects send bus to send dry signal to interface channel 1 and stomp out to interface channel 2. You can use DI between stomp and interface or engage interface HiZ input. I would try only connecting USB to interface and use power supply for stomp.

[finotti]

Thanks everyone for the responses!

@finotti I'm not familiar with the particular hardware you are using, but the symptoms definitely sound like a ground loop: the HX Stomp is sending signal to channel two of the Focusrite interface which is "ungrounded" compared to the signal from the DI to channel one.

Can you try toggling the "Lift" switch on the DI box? On the (much cheaper) DIs I use, that would make a huge difference.

I did try the "ground lift" switch and it did not help...

@finotti please describe the kind of noise or record it and attach to a post. There are many causes for the noise, but the "kind" of noise can address the root cause.

You can find a small clip here. Note all the noise when the lead/theme guitar comes in.

Sounds like ground loop. Not sure if it would make a difference but if I had to wire this configuration I would plug guitar into stomp box, use effects send bus to send dry signal to interface channel 1 and stomp out to interface channel 2. You can use DI between stomp and interface or engage interface HiZ input. I would try only connecting USB to interface and use power supply for stomp.

I might try that. But I really wanted to keep the DI signal as "pure" as possible, i.e., guitar -> cable -> direct box -> balanced cable -> interface. But maybe that could be a reasonable compromise.

Although less than ideal, I am thinking of only using the HX Stopm to reamp, and always use the DI signal with plugins to record originally. Then I can use the HX Stomp itself as an interface to reamp the DI signal.'

Or is there anything I can do to avoid ground loops?

[bluzee]

Reading the manual... If you use the Stomp box USB interface and plug guitar into input L/mono then there is dry guitar on USB input 5 in your computer and processed audio on USB input 1-2 and 3-4. You can eliminate the Focusrite and the DI. Have you tried this? Is the sound quality from the Stomp insufficient?

[finotti]

Reading the manual... If you use the Stomp box USB interface and plug guitar into input L/mono then there is dry guitar on USB input 5 in your computer and processed audio on USB input 1-2 and 3-4. You can eliminate the Focusrite and the DI. Have you tried this? Is the sound quality from the Stomp insufficient?

I should test it more thoroughly, but my impression that the quality of the direct signal recording through the HX Stomp is not as good as the quality when using my direct box and going to the 2i2.

But this was not very scientific. I will see if I can test it more carefully soon.

[bluzee]

I should test it more thoroughly, but my impression that the quality of the direct signal recording through the HX Stomp is not as good as the quality when using my direct box and going to the 2i2.

By using a DI and going through the Focusrite mic pre you are getting colour from the pre. That can be good or bad. The Focusrite may also use a higher quality ADC/DAC.

Personally I plug guitar direct into the HiZ input on the interface and send that dry to one track. Using JACK I also send that to the amp sim plugins rack then to interface outs and monitor over the PA. Latency for monitoring isn't a problem.

For your setup having the loop from one device to the other while having both connected via USB seems like a possible problem spot, but these things can creep into the oddest places and all you can really do is start unplugging stuff and see what makes it go away.

[kamiluni]

Uhm...do you refer to the hiss?
If it is so, it don't seems noise but a sort of Larsen effect, and in the case you have some feedback.