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Trying to figure out electrical hum in signal


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Hey all,

 

So almost a year ago I moved across the country for grad school, studying screen scoring. I was subletting at my old place and just moved into a new apartment a month ago—cheaper rent, but also with a third bedroom that is serving as a dedicated office/studio space. Bought a new desk that's big enough for my gear, inherited my roommate's old monitor, and all of a sudden I have a pretty fantastic setup. Problem is, I've got some kind of electrical interference and I'm both trying to troubleshoot it and eliminate it.

 

Current setup is my MBP, drawing power from my Anker PowerExpand Elite 13-in-1 dock, to which my Scarlett 2i4 first gen is also connected. The Focusrite is outputting the sound to my Mackie Big Knob Studio because I needed my monitors to also work for my stage piano and my girlfriend's computer when she needs to use the workspace. (She just uses the USB connection from the Big Knob.) Using headphones on the Focusrite, I don't have the issue. If I use the Big Knob as my audio interface, the problem is almost entirely gone (really gotta crank up the signal to a level I'd never practically use in order to hear any interference or noise). If I connect the Focusrite to a different USB hub running off the other Thunderbolt bus, the problem decreases, but remains. I know I've got some redundancy in my setup, but I do plan on investing in a better interface within the next year to replace my old FireWire Duet, so this will ultimately be my setup. Any input on how I can figure out how to eliminate the issue? Thanks!

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Is the hum there when you turn on the speakers?

 

It's not. In fact, it disappears if I turn off those channels on the Big Knob. If I'm just playing the piano, it's pretty silent. Haven't tried switching the inputs yet (the Scarlett is running into the combo ports on the Big Knob), but I'm thinking it has to be the USB running into the Anker dock and/or the 1/4" cables running from interface to monitor controller. If I'm right, I just don't know what I can do to fix it.

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Hard to pinpoint hum sometimes.

But when you turn certain things on and the hum shows up, you can trace it better.

Sometimes there's no fix, and the only way is not using that gear combination.

As long as the hum doesn't get printed, should be ok though.

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Oh yeah, it's completely out of the recording signal, only shows up in the monitoring on the back end. Just gets annoying hearing that while working (it's not the conventional hum, but more of an infrequent staticky sound—even tried to rule out wifi/bluetooth/cellular signals to no avail). I guess I'll keep experimenting to see if there's a setup or even physical layout that fixes this for me. Thanks as always!
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So I finally had a light bulb moment just now while checking out my new headphones. Still using the Big Knob as the interface at the moment, but the same crackling sound started popping up in there again. Since the Anker Thunderbolt dock wasn't mission critical at the moment, I quit Logic, ejected my sample drive, and turned it off. Boom, crackling gone. So now I need to see what I can do to isolate it (and hopefully not have to replace it, because it was a gift after I did TONS of research to find a unit with the right ports for my needs).
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More info: went to Google and came across a very similar thread over at Gearspace, and it turns out that a lot of people are having similar issues but with the CalDigit TS3+. It seems that somehow when the dock is also functioning as the MBPs power supply, the same type of static crops up. I didn't notice until reading it here, but the fluctuations in the sound do often seem to coincide with changing connections to the dock or even just operating the computer. Further, though the 16" MBP is mentioned a lot, others also mention older MBPs that are still of the all-TB3/USB3-ports variety.

 

So I tried a suggestion from that thread and connected the stock power supply, and wouldn't you know it, sound overwhelmingly eliminated. In my new cans I can still hear a faint static but it's manageable compared to what I was dealing with before. Downside is, I have to reconsider my connections to the computer now, and maybe buy a second adapter or dock to free up some room if I make some of the upgrades I'm considering. Hopefully this is the kind of thing that can be fixed in a firmware update, but considering that Silicon 16"s have to be on the way and this model already seemed to have issues with heating/GPUs when connected to an external display, I'm hoping this model doesn't become the forgotten bastard stepchild…

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Great find, power supplies can be a noise source for sure!

 

Yeah, that was the common finding in that Gearspace thread with the CalDigit docks! Makes me wonder if Anker is as informed about such things. Maybe I'll have to see if I can reach out to them to see if they know anything, or if they're able to replace the PSU as CalDigit have apparently been doing for their customers.

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