10 Hz and 50 Hz noise from cable, why?

[God Of Atheism]

If I connect an xlr cable to my audio interface, it creates noise at 10 Hz and at 50 Hz. The latter can be explained by the mains electricity. But why the former?

That the cable is dodgy seems clear, but why the noise at 10 Hz (and harmonics)?

I've attached several spectrum plots made using Audacity. I recorded nothing for 20 seconds or so and then used the plot spectrum function of said program to get the plot.
Since there seemed to be no difference between input 1 and 2, for these I kept the xlr cable at input 2 and a jack cable at input 1. Both inputs have a line and an inst setting, and I plotted both for each. Gain was set to maximum, both cables were only connected on one end.

The source of this experiment is noticing a lot of noise with frequency lower than the low B when recording bass and isolating the noise source.

 

[beans-on-toast]

One would need some test equipment to verify what is really going on. For the 10hz, I wouldn't rule out an artifact related to a software bug. At the same time, a cable can act as an antenna and pick up whatever it is presented with. Submarines use low frequency communication systems that operate in that region.

 

[silky smoove]

If you bounce a file out of the system (record an arbitrary 10-seconds of dead air while the 10 and 50hz information is present) and then import the result back into your DAW without having any cables hooked up do you still see this behavior? I'm trying to determine if there's something in the software like @beans-on-toast has suggested, if it's something in the monitoring path put there by the software for some reason, or if it's actually making it into the recording signal path from an external source.

 

[God Of Atheism]

@silky smoove , you mean recording with the cable connected, saving the recording, quitting the DAW, then disconnecting the cable, then restarting the DAW and opening the recording? In that case it's still there, but I'm not sure that's what you meant.

@beans-on-toast , I checked the firmware version of the audio interface, and it is old. I'm going to try and upgrade it. I'm not close to any seas, so also not close to any submarines. I mean there's a venue here named 'Yellow Submarine', but that's another thing. And then, why would an XLR cable work like an antenna and a jack cable not?

I also thought that maybe it had to do with phantom power being supplied, but switching the phantom power made it worse (similar, but louder), leading me to conclude that the initial settings were without phantom power (as I assumed, but the switch has no indication of in which position it's enabled or disabled). It might of course also be a hardware problem to do with that, I guess I also need to check what happens with a balanced jack cable, but I don't think I have any.

 

[beans-on-toast]

Noise is an issue that plagues audio systems and the causes are not always easy to pin down.

An XLR system is designed to cancel hum: Invalid Link Removed hum can still get in there which is where a ground lift can often help. This has to do with different ground potentials at each end of the cable. This causes a ground loop and line level hum. Search for noise in XLR cables for additional references.

Good cable management dictates that the cable length should be as short as is necessary. There are limits on the sending and recieving amps at each end. Shielding is also important. Higher end equipment performs better. Don't loop or wind up the cable if it is longer than you need, it is better to snake it back and forth along the floor. This reduces inductance. Use a good quality cable.

Clean power is also good to have. Bad wiring in your building can throw off noise. As I mentioned earlier, external influences can overwhelm any design measures intended to reduce noise.

There is always the possibility of a hardware or software issue.

 

[silky smoove]

@silky smoove , you mean recording with the cable connected, saving the recording, quitting the DAW, then disconnecting the cable, then restarting the DAW and opening the recording? In that case it's still there, but I'm not sure that's what you meant.

No, that's not what I mean. Follow these steps and report your results.

1. Attach an XLR to your system.
2. Confirm that you're now seeing the 10hz and 50hz signal represented within a session in your DAW.
3. Record 10-seconds of dead air from the session after confirming that the 10/50 signals are present.
4. Bounce the session down to a stereo wave file.
5. Close the current session.
6. Start a new session.
7. Remove all XLR cables.
8. Confrim that the 10hz and 50hz signals are no longer present.
9. In your new 10/50-free session, import the wave file you bounced out of the session previously.
10. Now, with all XLR cables still removed from your system, does the imported wave file contain the 10hz and 50hz content from the previous session's recording, or is it now gone?

Follow those steps EXACTLY. If you alter a single step you'll lose the objectivity of the exercise.

 

[God Of Atheism]

I finally got around to opening up the cable, and saw something rather unpleasant. Apart from single conductor cable being used, it also seems the wrong pins were soldered together to the shield, though I'm not sure since I already dismantled the cable. I replaced the wire with a proper two conductor shielded cable, and that solved the problem.

 

[beans-on-toast]

Congratulations on resolving the problem.

The soldering is a bit of a mess. I see a loose strand, that's all it takes.

I like to use a four conductor cable with a shield. The shield goes to pin-1, one twisted pair goes to pin-2, another twisted pair goes to pin-3. These type of cables are quieter.