in need of some expertise and guidance

[Greg Miller]

Since your voice level is so different in the three tests, it's hard to find a reference point.

However, the mystery 120 frequency is present in test #1, but absent in test #2 and test #3. So think about what different gear was on / off in those tests.

Aside from the 120 Hz, all the mains harmonics are present in all three tests (whatever the exact level).

Early on I suggested trying a different mic cable. Did you ever do that?

How is the dBx connected to the M-Audio? Any possibility there's a missing ground connection there?

Also, is your mic physically grounded in any way? I would guess it's not ... isolated by rubber o-rings, plastic hardware, etc. But just looking for the source of some ground loop.

What kind of power wiring in your house? Romex? Knob-and-tube? Metal conduit? PVC conduit?

Where is your "studio" relative to your house's power entrance panel?

What happens if you leave all the settings as-is, then unplug the mic from the mic cable? Then unplug the mic cable from the dBx?

[Paul R Johnson]

You're doing a fine job Greg, I'll leave it with you. I still think we haven't got the entire picture. Speakers entered the discussion, and I figured there were no computer monitors turned on, yet the hum and harmonics were still present.

Not to worry, you'll sorry it, I'm sure.

[Greg Miller]

I would have guessed an open shield on the mic cable, but then the phantom power wouldn't work. I asked about the cable long ago, but the OP hasn't responded to that question. Methinks he's overwhelmed by all the variables. I am really wanting to know about the lineage of that mic cable. OTOH there is no hum when he runs the mic directly into the USB interface. Again, what cable(s) are in use? I need to pin him down about this detail.

Actually it would be quicker for me to fly there and look things over myself; but I'm sure there are travel restrictions ...

[Paul Mailath]

Hi Greg et al,

sorry for my delay, I'm trying to get some editing jobs out of the way (voice over is only a sideline and I can't really do without the setup I have but if I can change thigs around then I'm keen to find a solution.

Cables
the XLR cables and the long USB cable are certanly not new (10 years+) and they are consistant througout every test (I haven't swapped any. ** perhaps the next step is to get some new cables and try those *** I just realised that the output of the DBX is a 1/4 TRS and the cable converts to XLR

Mike
I do have an old Berhinger but god knows where it is

XLR to USB interface
I'm currently using the M-Audio but that's also could be 10 years old so maybe it's time for a replacement.

Mystery 120Hz
in test 2 I switched off both computers and all the battery chargers - I hoping it's the battery chargers - perhaps the next test is is with my original setup but all the battery chargers off - then one using the laptop to record the same with a different USB cable.

How is the dBx connected to the M-Audio?
1/4 TRS to XLR cable, I think the cable came with the unit

Also, is your mic physically grounded in any way?
this is the setup
https://www.broadcastbruce.com/produ...kaAgo2EALw_wcB

What kind of power wiring in your house?
not sure but I think it would be Romex - it's about 60 year old - certainly haven't seen the others in the roof only cable


Where is your "studio" relative to your house's power entrance panel?
either ends of the house 15-20m (45Ft)

What happens if you leave all the settings as-is, then unplug the mic from the mic cable? Then unplug the mic cable from the dBx?
not sure I understand this - are you suggesting I start recording then unplug the mic end of the XLR cable and then unplug the DBX end of the cable?

I'll run some more test tomorrow powering everthing off at the wall, running an extension cord from another room and using the laptop on battery.

I'll order new XLR cables and a XLR to USB but those won't come till late next week (I'm in a regional area)

thx for your advice and patience

[Greg Miller]

I tend to think the mic cable is OK. Normally there are two signal wires (white, black) and a woven shield which also grounds the mic to the preamp. If you were using a dynamic mic, and the shield connection were open, you'd still get audio from the mic, but would be very susceptible to hum and electrical noise.

However, you're using a condenser mic that gets phantom power DC from the preamp. Without a ground connection, the phantom power won't work and you won't get any audio. It is very slightly possible that you have a mic cable with three conductors: black, white, ground (probably green) PLUS a shield. If the ground is good the phantom power would work. Then if the shield is NOT good and the signal wires aren't shielded, you could have noise problems. This seems like a slim possibility at best.

The dBx has a three pole AC power connector. Is it connected to a properly grounded mains socket? ... no UPS, no extension cord, just a known good connection to a known grounded socket?

Too bad dBx omitted a headphone jack, that would have been a simple test point.

- - -

Let's take one step at a time to minimize the confusion.

I'd really like to hear a test with *everything* turned off and unplugged. That includes turning off and unplugging the UPS units. The only thing plugged in should be the dBx, directly into a known grounded outlet. Then the dBx feeding the M-Audio, and the M-Audio feeding (and powered from) the laptop which is running on batteries.

BTW, I want to confirm that you are *not* using an external wall-wart with the M-Audio, powering it only from the computer's USB cable. Is that right?

[Greg Miller]

Originally Posted by Paul Mailath

XLR to USB interface
I'm currently using the M-Audio

Just to confirm, that's the Fast Track Pro version, not the original Fast Track (without Pro in the name). Is that correct?

Originally Posted by Paul Mailath

Mystery 120Hz
in test 2 I switched off both computers and all the battery chargers - I hoping it's the battery chargers

No, the battery chargers run on your 50Hz mains, and might put out harmonics of 50Hz. But 120 is not a multiple of 50. I'm sticking with my original theory that the 120Hz noise originates in a computer monitor with either a 60Hz or 120Hz refresh rate. I've previously mentioned this several times.

Originally Posted by Paul Mailath

What kind of power wiring in your house?
not sure but I think it would be Romex - it's about 60 year old - certainly haven't seen the others in the roof only cable

Romex should not be troublesome. The one that can be terrible for AC mains noise is the old knob-and-tube wiring scheme.

I don't know what you mean by "roof only cable." Maybe some Aussie terminology I'm not familiar with?

Question #1: Is your house wiring earthed? Do all your mains sockets have the third terminal for safety/earth pin?

Originally Posted by Paul Mailath

Where is your "studio" relative to your house's power entrance panel?
either ends of the house 15-20m (45Ft)

That's as good as possible.

Originally Posted by Paul Mailath

are you suggesting I start recording then unplug the mic end of the XLR cable and then unplug the DBX end of the cable?

Exactly. Everything unplugged and turned off, except the dBx plugged directly into mains. And I do mean unplugged. Even with power turned off, the ground connection in power cords can create ground loops.

For that matter, go around the house and turn off anything with a motor, any LED lights or fluorescent lights or lights on dimmers. Turn off any baseboard electric heat, radiant heat cable e.g. in the plaster ceiling or floor. (Honestly, if your dBx would run on DC, I'd tell you to turn off the main disconnect breaker for the entire house.)

Connect mic > XLR cable > dBx > converter cable > M-Audio > USB cable > laptop, which is unplugged and running on its internal battery. All dBx processing disabled. Record a few sentences at normal level.

Pause the recording. Power down dBx. Unplug mic from its end of the cable. Power up dBx. Resume recording ... capture 15-20 seconds like this.

Then Pause the recording again. Unplug input cable (XLR) from dBx. Resume recording ... capture another 15-20 seconds like this.

That should tell us a lot.

By the way, are you monitoring on headphones? You mentioned speakers earlier, but never talked about them getting AC power from anywhere. Any powered speakers should also be unplugged and turned off.

Originally Posted by Paul Mailath

I'll run some more test tomorrow powering everthing off at the wall, running an extension cord from another room

I'm not sure I understand the point of the extension cord. If you are talking about power for the dBx, it needs to be plugged directly into the closest mains outlet. Presumably you have mains outlets in your "studio" room, right???

Question #2: Where is the dBx located with regard to other electronics in the room? How is it mounted?

[Paul Mailath]

boy I'm learning a lot using google - 'wall wart' I like it!

The fastrack is not the pro version, it's the original and is powered via USB from the computer or laptop

Monitors
I checked & 3 monitors were on 60Hz, one on 59Hz - I changed 3 back to 50Hx but the last monitor doesn't have another option (I guess I'll be replacing that one)


Power cables
I meant to say haven't seen any other type of cable in the roof, only Romex

Headphones
I use these to monitor out of the Fast Track (if the DBX had monitor out, the fast track could go)


I'll run the 'everything off' tests later today and upload

[Greg Miller]

Paul, I am trying to solve a problem for you, but without complete information. Please read and answer the below questions before we go any further.


First, please answer the two questions in bold font in post #36!


Also, why do you need to run an extension cord from another room in your house? Why not power the dBx from a socket in your "studio" room?


Also, what do you mean by "3 monitors were on 60Hz, one on 59Hz"? What does "were on" mean in this sentence? What are you changing?


Finally, your Rode NT1A requires phantom power, right? From what I can find online, the original Fast Track does not have phantom power. (The Fast Track Pro does have phantom, but you said your unit is *not* the Pro). So how did you record your original sample allegedly with the NT1A directly into the Fast Track? Something seems not to make sense. Can you clear up the confusion?

[Paul Mailath]

Sorry Greg, I missed those

Is your house wiring earthed?
I assume so, all the wall sockets are 3 pin
https://www.sparkydirect.com.au/p/20...RoCajwQAvD_BwE

Where is the dBx located
The DBX is inside the booth (I've attached pics)
(even considering the fact that I'm 65, I'm feeling rather like a schoolboy in front of the principal ATM)

I have a feeling you're not going to like this - the DBX is actually suspended from a rack mounted on the wall where I put my scripts.I meant to mount it above the booth once I had settings I liked but never got around to it.

The booth is in a corner of the room *floorplan attached

I ran the extension cord into another room rather than unplug all the battery chargers and move the cupboard out to get the the powerpoint directly

You mentioned that you felt the 60 or 120 signal was coming from the monitors so I checked and they were set at 60Hz so I changed them - I can change them back if you wish

The M-Audio Fast Track does not have the word 'Pro' anywhere but does provide phantom power

M-Audio - Fast Track - Pro Tools MPowered Essential - YouTube

I think that's it - I really do appreciate your time on this and I'll get on to the next set of tests ASAP

[Greg Miller]

Paul, thanks for the additional info. The photos and floorplan are a big help! Sorry if I sound overly austere but it's getting frustrating when I ask a specific question -- perhaps more than once -- with no apparent response.

My concern about the dBx was that it might have been mounted in a rack with a bunch of other equipment, either creating noise or ground loops. So the fact that it's hanging there might not be a bad thing.

I'm a bit puzzled about the battery chargers. You were going to power the dBx via an extension cord, "rather than unplug all the battery chargers." But when you record the next few tests, aren't you going to unplug the battery chargers (and everything else) anyway?

Also, comparing the booth interior and exterior photos, on the outside wall I see what appears to be a mains socket, and a hanging power "octopus" mounted on, or hanging against, the booth wall. What's on the other side of that wall? Is that where the dBx, mic, etc. are located?

And what all is plugged into those "octopus" sockets? Are those the battery chargers?

Also, once again, the monitors. You said "I checked and they were set at 60Hz so I changed them." "changed them" is meaningless, and I asked before, what do you mean by this? Did you change a switch somewhere (if so, where)? Did you change a video driver in your computer(s) ... if so, provide details. Write a descriptive paragraph about this. I want to know what you did. It may give us some relevant information.

Now that I see the floor plan and see that the computer displays are not close to the mic, this becomes more bizarre. It seems strange that electrical noise from the monitors would find its way over to the booth. Even so, I want to understand what you changed.

Also, when you record some new tests onto a laptop (running only on internal battery), out of curiosity where will the laptop be located, relative to the rest of the room?

- - -

It's now 2:00 AM here so I'm going to sleep. I'll check in after I'm up and about on Saturday.

[Paul Mailath]

Hi Greg, I understand completely, I think I've skipped over some points and questions in my confusion, I need to be more analyitical.


I'm a bit puzzled about the battery chargers. You were going to power the dBx via an extension cord, "rather than unplug all the battery chargers." But when you record the next few tests, aren't you going to unplug the battery chargers (and everything else) anyway?

**Yes, to get to the powerpoint directly I have to move the side cupboard which means unplugging all to the battery chargers and moving them out of the way - the extension cord was my lazy way of getting around that but I see it's not the right way to go.

Also, comparing the booth interior and exterior photos, on the outside wall I see what appears to be a mains socket, and a hanging power "octopus" mounted on, or hanging against, the booth wall. What's on the other side of that wall? Is that where the dBx, mic, etc. are located?

**yes

And what all is plugged into those "octopus" sockets? Are those the battery chargers?

**yes

Also, once again, the monitors. You said "I checked and they were set at 60Hz so I changed them." "changed them" is meaningless, and I asked before, what do you mean by this? Did you change a switch somewhere (if so, where)? Did you change a video driver in your computer(s) ... if so, provide details. Write a descriptive paragraph about this. I want to know what you did. It may give us some relevant information.

**these are the steps I followed:
https://www.windowscentral.com/how-c...ate-windows-10

My assumption was/is that this would solve that part of the problem. As I understand it I've changed the refresh rate

Now that I see the floor plan and see that the computer displays are not close to the mic, this becomes more bizarre. It seems strange that electrical noise from the monitors would find its way over to the booth. Even so, I want to understand what you changed.

** the scale of the floorplan is rough. The nearest monitor is 1.8 metres from the mike


Also, when you record some new tests onto a laptop (running only on internal battery), out of curiosity where will the laptop be located, relative to the rest of the room?

** the laptop will be near the monitors, about 2 metres away. I was thinking ot running a seperate test using a different USB cable in which case the laptop would be next to the booth.

I'll get that done tomorrow

[Paul R Johnson]

The frustration is that you seem to want to ignore the systematic approach.

If the computer monitors are causing the noise - unplug the damn things and do a recording. We've no idea what changes occur when you change settings - unplugging takes the item totally out of the equation.

On things like the the possibility of it being a mains power situation, if you have loads of adaptors and cables, you have to go back to basics and have as little kit as possible.

I don't know why you cannot just take a socket on the wall, power up the minimum kit - not even the powered speakers - and just do a recording with the minimum kit, and then add item by item till it gets noisy!

[Greg Miller]

Amen, Paul!

My frustration is that the OP ignores specific instructions. e.g. "turn off and unplug everything" does not mean "change some video settings in your computer."

Also e.g. I said specifically that mic wiring should be as far as possible from power wiring. Yet here's an octopus, feeding a handful of battery chargers, hanging on the booth partition wall directly opposite the location of the mic and preamp. Yet that seems to have completely escaped him until I saw the photos and floor plan and asked specifically about it.

We are basically breaking down what is just "common sense" into minute steps, but he wants to improvise other steps instead.

[Paul R Johnson]

I got some strange noises last year, and investigations pointed towards the radio repeater in a space two rooms away. In the end, after trying everything - the cause was the 1U light in the top slot of the rack cabinet. switch mode dimmer for a little LED on a gooseneck, illuminating the equipment. Obviously killing the rack power solved the buzz in the studio, but all efforts went into the rack mount radio gear - even using the hum-free isolating hardware to separate the rack from the repeater, with no real reduction but a change in the harmonics. pulling out the tiny power supply to the light silenced everything.

I now never try to diagnose these things without starting from scratch and building up. You asked about the interface and USB powering vs external PSU - did that get picked up on?

[Greg Miller]

Yes, that was answered. He seems to have a rarely-documented version of the interface. The original version is documented not to have phantom, which really puzzled me. There is a later "Pro" version which does have phantom (and also wal-wart power option). OP swears his is not the "Pro" but does have phantom. At any rate, his is powered by USB from the computer. And that test recording (sans dBx) did not have any mains hum.

I think your idea of starting from scratch is a good one! Make one piece of gear work. Then add one more piece ... does it still work? Etc. Eventually you will find the offender.

I wonder whether he has single phase power, or split phase power, in his house.

He could always get a Sound Devices recorder, with good preamps, run it off battery, and throw out everything else.