I've been doing voiceover for some years as a sideline to my acting & video work, usually 4 to 6 jobs a month off local studios or upwork.

I use to have a walk-in robe is a spare room lined with soundproofing and it worked quite well till the wife wanted her storage back - kicked out for for some linen!

So.. I build a booth in my office. Marine ply around a frame with rubber sound deadening & acoustic insulation. it's pretty dead, perhaps a bit too dead but it's been working okay *pic & recent pickup for job attached

in the old location I used an M-Audio Fast Track to convert to usb into the computer. in the new booth I've added a pre-amp.

My current setup is a Rode NT1-A to the DBX 286svia XLR then to the M-Audio via XLR then to the computer via USB and seems to be working okay to my tired old ears.

With no video or acting work I really need to step up my game with voice over,which brings me to my point. In checking my settings I noticed a hum when I bypassed the DBX - it's a low hum. If I remove the DBX completely and run from the Rode to the M-audio - I get a high hum?? *sound test attached

I'm not really sure where to go from here, is this something I need to sort out? can I leave the DBX to eliminate it?

any suggestion will be gleefully accepted

here's something I'm also working on - https://drive.google.com/open?id=1tA-PM5nGlsVePhv5hZMsg1JsNdlkhMds

Nasty resonances you've got happening there. You sounds like a right Aussie. :-)

Seriously, the Google Drive video snippet sounds really good for the voice. Just had a very quick spot listen.

Andrew

I noticed a hum when I bypassed the DBX - it's a low hum. If I remove the DBX completely and run from the Rode to the M-audio - I get a high hum?? *sound test attached

Clearly the second part of your track has a lot of mains (and related harmonics) hum. I'm a bit confused about your use of the term "bypass" in your sample track. On the dBx, "bypass" means you are bypassing all the processing (in other words using just the preamp section). So "bypass" is not a thing in itself. "Bypass" is the absence of something (i.e. the absence of processing). So to say your are "turning bypass off" is confusing. You are turning off off.

So to clarify ... in the second section of your track, which affects the noise sample from 14.0 to 18.5 seconds, you say you are going to "switch the bypass off." Do you mean you are taking the dBx out of "bypass" mode ... in other words engaging all the processing sections? Or do you mean you turning off the processing sections, by engaging the "bypass" mode?

As far as the third part of your track, with the noise sample from 24.0 seconds to the end, the high pitched tone is almost surely a bunch of noise from the digital converter in the M-Audio box. It's too high in frequency to be related to your mains power. Did you have that noise all along (before you added the dBx to the signal path)? If all Fast Tracks have that amount of noise, I'd say they're not suitable for serious use. If this occurs only with your setup, I'd guess your Fast Track is defective. (Slim chance it's a shielding or grounding issue with your mic, but given that we don't hear it with the dBx in line, I think it's more likely the mic preamp in the Fast Track.)

- - -

The Ripple Effect sample has so much editing going on that it's hard to tell too much about the audio (aside from making the pacing sound unnatural). However, there are three very obvious bits of noise. One is after "Queensland" at 16.3 seconds. The second is after "thinking" at 22.57 seconds. The third is after "paddock" at 23.55 seconds. In all three cases, immediately after the word, I hear hum and hiss start to fade up. (which you immediately snip out presumably by means of editing) That indicates to me that you have some compression engaged, so, in the absence of desired voice, the compression is raising the system gain, bringing up the noise.

You sounds like a right Aussie. :-)


it's hard to miss eh! while I can tone it down, the majority of my VO work is 'the aussies farmer/ butcher etc - you work with what you've got

I do need to broaden my range but the 1st thing is to get the technical stuff right

Winston Churchill said that the Australian accent was ‘The most brutal maltreatment that has ever been inflicted on the mother-tongue of the great English-speaking nations.”

Hi Greg,

you're quite right - I had it the wrong way round
0-14 processing is on
14-18.5 processing is off
24-28 DBX is removed from the process - mike goes straight to the M-audio

The M-audio is pretty old so I'm happy to bin that and find another xlr to USB converter - I can get the Shure X2U XLR-to-USB locally.

As far as the mains & related harmonics hum is concerned - I'm not sure what that means but could it have something to do with the power cable for the DBX being connected to a powerboard with a mass of battery chargers for all my cameras? Perhaps I should run a lead to a powerpoint wiht nothing else connected.

If I can get rid of the noise/hum then perhaps I can minimise the processing from the DBX (I know it's a fairly cheap model but it has served it's purpose. I've really been dialing in settings at random to get what I think is a reasonable output (and obviously that's not been good)

Paul,

The dBx cannot remove any noise originating in the M-Audio. I don't hear any noise in the first section. Therefore I assume you are sending a line-level signal from the dBx to the line input on the M-Audio. Since that sounds fine, I think we can just ignore the M-Audio for the moment.

While the noise in the second section sounds terrible, the important measurement is the signal to noise ratio usually expressed in dB. In other words, how loud is the noise relative to the desired signal. Just hearing a section of noise, without knowing all the conditions producing the noise, is not terribly helpful.

I would like to hear a new test with the mic going through the dBx preamp, but with all processing bypassed. (The processing can fool us and make the noise sound louder or softer than its actual level.) With that configuration, record some voice at a proper level. Then without changing anything, just stop talking for 20 - 30 seconds so we can hear and measure the noise (relative to the level of the speech).

Hi Greg,

here's the 2nd test - all processing bypassed with a quick read and 30s of silence - recorded in Audition, no effects.

The noise floor (is that what it's called?) still has that hum

The file is too big for DVinfo so here's a link:
https://drive.google.com/open?id=1w2b6e0VWznO4a2niehpI6lCOM_NVaHFm

Thanks, Paul, that is a very useful sample track.

Your voice peaks are around -5dBFS, which is OK (although perhaps a bit higher than some folks would like). It leaves 5dB of headroom before the gear starts clipping, so you daren't record any hotter than that. The noise peaks fall around -52dBFS which is rather high. That puts the noise ~ -47dB below the voice peaks. That is not adequate S/N (signal to noise) ratio. So yes, this problem should be addressed.

What I hear is a harmonically rich hum related to your 50Hz power mains. By harmonically rich, I mean that, like a piano string, or most musical instruments in general (perhaps excepting a Theramin), there are harmonics that are mathematically related to the 50Hz fundamental frequency. In this case I also see 100Hz, 150Hz, 200Hz, etc. and the harmonics continue, at varying levels, up into the thousands of Hz. Indeed, that could be originating from switching-type AC power adapters or battery chargers. Many countries now insist that all AC adapters are switching-type because they are more energy efficient. So unless you have some fairly old chargers, I'll bet most of them are this type.

Lamp dimmers can also cause the same kind of noise related to mains power and harmonics. Are there any lamp dimmers in use, especially near the sound gear?

As a general rule, all audio gear that is interconnected should get its power from the same outlet if possible. So I suggest you plug the dBx AC adapter into the same outlet where your computer is plugged. And, if possible, get all the chargers away from that outlet. (Of course they might still end up on the same circuit, because of your house wiring; but at least get them physically separated.)

Also, in theory, the preamp, M-Audio converter, and computer should have their earth connections tied together. But this is often overlooked and sometimes even difficult to do, given the present state of computer wiring. Let's pass over this for now, but keep it in the back of our minds.

It is also possible that this AC mains noise is being picked up by the wiring between your mic and the preamp. Is that mic cable properly shielded? Does it properly ground the mic? Is it a reasonable length? Is it physically separated from all those AC adapters and other AC power wiring? If it's absolutely unavoidable to keep the mic cable from crossing over a power cable, they should cross at right angles.

Incidentally, I recall that when the mic was connected directly to the M-Audio input, the signal contained a lot of high frequency noise that I'd associate with computer gear. If there's something wrong with your mic cable, that might cause the two different types of noise to be picked up in the two different scenarios. So don't rule out the mic cable as the culprit.

Of course the mic itself should not be near any power supplies. Also, some computer screens radiate a fair amount of AC noise, so consider whether the mic (or wiring) is close to a display.

*** By the way, your noise sample also contains significant content around 120Hz. This is not a component of the 50Hz mains power. It might be related to a computer display with 60Hz or 120Hz scan rate. So be sure to consider proximity of the mic to any display! God help you if you have an old plasma TV nearby ... they radiate crap all over the spectrum.

Lots of things to try. You can change one thing at a time, to try to scientifically find the source of the problem. Try listening while you move things around, plug and unplug things, turn things on and off, etc. Or you can just use the "shotgun approach" ... change a whole bunch of stuff at once and see whether you've killed the offending noise.

I'll be interested to hear what you find out.

Good luck!

Remember that most VO artists are not technically advanced, their income from their voice just needs clarity, no room and no noise. When they submit work, it needs simply to be EQ'able and clean. That's all!

Remember that most VO artists are not technically advanced, their income from their voice just needs clarity, no room and no noise. When they submit work, it needs simply to be EQ'able and clean. That's all!

I would think that "clean" includes fixing the -51dB hum from the power mains frequency & harmonics.

Absolutely, but my thinking is that the simplest path is often the best for many. Mic, modest interface, laptop - done! Hums aren't part of clean.

wow! thx Greg - lots to work on there

I'll test and get back to you

I'm actually now concerned with the amount of electronic gear I have in the room which could be affecting things:
2 large desktop computers, 4 screens & 1 laptop
3 synology servers with 3 UPS backup units, printer and the aforementioned shitoad of battery chargers.

I might have to take the cupboard back - not looking forward to that battle.

If you read the previous posts in this thread, the OP had heard high frequency noise with his simpler setup, and when he added the new preamp the noise changed to mains hum. He's asking how to get a clean recording. All my answers were directed toward his getting a clean recording.

Since his previous combination of mic, simple interface, and PC did not yield "clean," what do you suggest other than the sort of trouble-shooting as I have recommended?

3 synology servers with 3 UPS backup units

I'll bet you dollars to donuts the UPS units are the problem. Almost all of them put out square waves, which by definition are full of harmonics. They get into audio, and can even wipe out AM radio reception. Get away from those and I'll wager your noise will be much less. By all means your preamp, and ideally your audio PC, should not be powered from those.

(Indeed, you can get much more expensive UPS units that have true sinewave output, rather than typical square wave or "stepped sine wave." But you will pay a lot more for those.)

Beyond the UPS units, every computer, every server, and every monitor has a switching power supply in it. That is a hell of a lot of electrical noise to have inside your live mic studio.

Small switch mode power supplies are usually the culprit for many noise related issues - Why not start with as clean a path as you can arrange, and gradually add your other items to see if it's one of them causing it, or the cumulative effect of all of them.

Rode - M Audio - Computer. everything else disconnected. Then add the DBX. If this causes the noise to ramp up - try disconnecting pin 1 on the XLR cable to the M Audio. If all is well, add the other stuff and repeat.

EDIT
Just noticed you mentioned UPS. Some designs regenerate the mains voltage, while others don't - it's possible your noise source emanates here?

I'm shooting tomorrow but as soon as I'm back I think I have to turn everything off exept the booth and I'll record into the laptop and see what happens - seems my editing setup is creating the audio room from hell

I'll bet you dollars to donuts the UPS units are the problem. Almost all of them put out square waves, which by definition are full of harmonics. They get into audio, and can even wipe out AM radio reception. Get away from those and I'll wager your noise will be much less.

that's a bugger, we tend to have brown-outs and the UPS was to supply power to the 3 RAID servers & both editing computers during those times. One of the computers records the audio.

would it be possible to put the UPS units in another room and run long extension cables to minimise the problem? (15ft further)?

Using a laptop (running for battery) with an SSD drive might sidestep all of these issues. You can record on that and then transfer to your RAID storage at the end of each recording session.

Andrew

would it be possible to put the UPS units in another room and run long extension cables to minimise the problem? (15ft further)?

First let me clarify what I've said before. Most UPS units do not put out clean sine wave, therefore they have lots of harmonics; however some UPS units do put out clean sine wave (thereby much less noise to worry about). We don't know which kind of units you have. (The clean ones are less common and more expensive, even so you may have these.) So this may be your only problem, or one of your problems, or not a problem at all. Just speculation until you try some tests.

A few years ago I had a real nightmare with UPS noise. I had included it here, but have decided to remove it because it isn't strictly applicable to your situation. Bottom line ... your extension cord solution may or may not work. The only way to tell is to try it. We haven't even definitely identified the source(s) yet.

I endorse Paul Johnson's approach: if possible turn off and/or unplug everything except the dBx and PC, see whether the noise is gone. If it is, then turn things on one by one until you find the culprit(s). If the noise isn't gone, then get the UPS units turned off and unplugged and see if that's the source.

I also like Andrew Smith's suggestion to use a separate laptop, battery powered and disconnected from the mains, to do your audio recording. Or, for that matter, you could use a shall portable audio recorder, again running on battery. In that case you could eliminate the M-Audio as well, just feed the dBx mic strip into the recorder. That may seem radical, but it may be the least radical of your alternatives.

Be of good cheer ... you may find just one insignificant piece of gear causing the problem. Don't forget to consider the physical proximity of the mic to all the other gear, especially display screens. That 120Hz frequency in your noise spectrum makes me suspect it is not all mains related (although that might be something picked up acoustically by the mic).

Let us know what you learn from your tests.

In my experience of live sound, you see somebody coming towards you with a laptop and cable. You know this is where the show audio is coming from. They get closer and you see the Apple symbol. You breath a sigh of relief because it's 99% certain they'll plug it into the mains (another relief) and the connectors will go into your left and right and everything stays silent and hum free.

They get a bit closer and you CAN'T see the Apple symbol and you start to think about where the DI boxes were last time you saw them, but you might not need them.

Then they get closer still and you see the words of doom - Dell - on the damn thing and start looking for the one DI box of your half a dozen that might get rid of some of the noise, but of course you can unplug their power supply and hope the batteries last. They then tell you the batteries are dodgy, but don't worry as they have the power supply.

People think it unfair to single them out, but this has happened so many times, seeing the word worries me. It happens on my old Dell too. I wonder if their policy of including a check of the power supply validity on their products is partly to blame? IS it data on the DC line that allows the laptop to identify the PSU? That irritating message that says the power supply is the incorrect one, and battery charging has been disabled convinces me something apart from DC is on the way into the laptop. Maybe this makes it worse? No idea, but that awful noise going through a 12K PA system can be disturbing in the extreme. Others do it to a degree, but Dells are the absolute worst, and loads of people run off batteries for this exact reason - but nobody seems to complain to Dell. EVERY Dell I've had for years does this, and their desktop machines are quite noisy too - not as bad as laptops, but I avoid them now if I can, apart from in the office running nothing audio or video.

My current setup is a Rode NT1-A to the DBX 286svia XLR then to the M-Audio via XLR then to the computer via USB and seems to be working okay to my tired old ears.

In my experience, electrical noise can enter electronics in a number of interesting and devious ways. The main ones are 1) through the mic cables, which is why we invented balanced XLR cables, 2) mains power, and 3) through the mics themselves.

Since you're already using XLR cables, I'm thinking you've probably taken care of #1. If you have a spare mic around that you can try in your existing chain of cables and devices, give it a try and see if your problem goes away or at least attenuates. That will quickly tell you if your mic is letting noise into the system. Since your mic is probably OK, that leaves power supply issues.

First thing to try is to turn everything off that you can -- all your extraneous computers, lights, HVAC, refrigerators, fans, etc. If the problem goes away or attenuates, start turning them back on, one at a time, testing as you go. This will help you find the culprit(s). But it won't help you deal with them really. Because the way you have to deal with them is to isolate them from your recording chain.

And the way to fully isolate them from your recording chain is to run your recording chain from a battery power supply that's giving you a pure sine wave output. Amazon lists a bunch (https://www.amazon.com/s?k=lithium+battery+power+station+pure+sine+wave&ref=nb_sb_noss) (which probably doesn't help you a lot in Australia, but gives you an idea of what you're looking for). These "portable power stations" come in all sizes, just be sure you see "pure sine wave output" in the specs. Run your entire recording chain off your portable power station so that you're completely isolated from everything else, including your local ground.

One other thing to consider is whether the noise problem is electrical or acoustical. The mic might just be telling what it hears in the room with you. A buzzing fluorescent light can make both electromagnetic and acoustical noise, for example. But again, if you turn everything off, this problem should go away or at least attenuate.

If you still have noise problems, it's beyond what I can trouble shoot from where I'm sitting. Sorry.

There are some important side issues here.
Firstly, few recording studios have to use UPS devices to remove hum and noise.

All the techniques here are trying to cure a fault, or a faulty device.

Critical factors are the fact that if we different ground potentials, then current flows. Sure, it causes noise, but it is trying to act as a protective measure to stop you dying!

Most power supplies nowadays are small switch mode devices and our UK ones have a plastic ground pin - needed for our sockets as they have a shutter fitted to prevent fingers being stuck in. Ground - the real safety ground outside tends to be connected in quite a lot of domestic buildings to the neutral line that feeds in with the live conductor. This means that there is a direct connection between the electrical power to the ground conductors in your home or studio. In the UK, adding extra grounds via rods outside (something we used to do to get a clean technical ground) is now not allowed. Multiple ground/earth points are now deemed electrically bad news.

We've covered the step by step connection system, and realistically, consider what we have? A pretty simple system. Mic, processor, interface, laptop. We have two sorts of noises - data buss noice and plain old fashioned hum. The data bus noise is coming from the computer down the USB cable then getting into the audio in the interface. The hum is probably coming ib via the DBX - but, is usually reliant on another ground connection to the system? Is the computer PSU a three conductor type with a ground? I assume it must be because hum like this needs either two ground sources, or none. If it is floating because the DBX isn't connected to real ground (two min mains cable??) nor is the computer, then you could try adding a ground connection to see if this improves the noise or makes it worse.

The data bus noise is going to the hardest to remove I suspect.

Curing that mains hum is the first thing to do. You're also compressing quite hard I note as when you speak the hum goes way down, but on the pauses, suddenly pops back in. Maybe you could back off a little on the compression, but that assumes you can find the origin of the hum.

Out of interest, what does it sound like plugged directly into the interface with the DBX unit removed from the chain completely?

what does it sound like plugged directly into the interface with the DBX unit removed from the chain completely?

He's already provided a sample of that, and it's been discussed in earlier posts. The hum goes away, and is replaced by data buss noise. The M-Audio's preamp is picking up data noise internally; the dBx is picking up mains hum. You might want to go back and check the thread from the beginning, it will answer a few questions, but will raise some new ones.

Thanks Greg. I did and just still want sure why the two issues seem to be linked or separate, and if the DBX is removing the data hash or just gating it off? Mic/interface only with and without the power supply will show if the power supply is the cause, or at least the route in. We don't know if the OP is doing the testing in the way we think he is. We've agreed on possible identification and now we are suggesting methods, but we can't advise if we're not sure of the exact circumstances. That's all. I'm not sure of the test conditions, that's all. Something simple could be in place and we don't know. If we guess it can't help.

Then they get closer still and you see the words of doom - Dell

laughs
looks over at the laptop
shit!!

okay,

I've run some more tests and recorded audio

1 - everything in the room on but recording via Audacity into the laptop

https://drive.google.com/open?id=1jkTVOFjRU2BGbjdcTx-783VkkY5nSWmX

2 - everything in the room off except the Synology servers and the ups

https://drive.google.com/open?id=1G-J4Cwps3sNjWIOrDzQnDZRXS9ohW43v

3 - everything off *powerpoints are still on but everything is switched off

https://drive.google.com/open?id=15RUAmyukU997Zu6Lx6QFUNutxYQ4sHSE

It's the quietest the room has ever been but I could still hear a faint hum and it was coming from the speakers. I switched those off and there is still a faint noise but I can't determine it's origin.

I can still the same hum when I bypass the DBX processing - buggered if I know

Paul - I'd be very interested in if your Dell can have it's headphone output connected to a grounded audio system with silence. I like the computers, just the connection headaches - so if yours is silent, the model would be very handy for knowing a good one!

On the audio file front.

It's not just being off - it's connected - because the ground paths are intact even when powered down.

I know it's a pain - but what would be good would be a comparison between the totally isolated simple path - mic - interface-laptop totally on batts.
then
same thing with power connected to the laptop. You also mention speakers? Are these active types, connected to mains power, or have we got an audio amp in the system too?

I just have the feeling we're not seeing the complete audio path. The DBX unit, even if powered down has a ground path, so would an amp, but the speakers often don't.

Those harmonics on the audio - is it me, or are they wrong? Looking at them they seem to be 60Hz, 120Hz etc - but is not Australia a 50Hz country like the UK? More mysteries as we go on?

Those harmonics on the audio - is it me, or are they wrong? Looking at them they seem to be 60Hz, 120Hz etc - but is not Australia a 50Hz country like the UK? More mysteries as we go on?

Paul, I have already mentioned that twice, in two earlier posts! My suspicion is a computer display running at either 60Hz or 120Hz scan rate. I have been very specific about this, including mentioning physical proximity between mic and any displays.

Thanks Greg. I did and just still want sure why the two issues seem to be linked or separate, and if the DBX is removing the data hash or just gating it off?

It's obvious from the samples provided that there is NO data hash in the sample where the mic goes through the dBx (but with all processing disabled). The dBx is not removing the hash ... it is not there to begin with. There is data hash only when the dBx was out of the picture, and the mic going straight into the M-Audio. I asked Paul to provide a sample of dBx noise, in "bypass" mode, specifically for this reason. It is very obvious from that sample. This is clear from previous audio samples and earlier posts.

okay,
I've run some more tests and recorded audio

Paul, the processors change the level of your voice. Therefore they make any signal-to-noise comparisons meaningless.

Please record *everything* including your voice with the processors bypassed.

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?

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.

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 ...

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/product/rode-nt1-a/?gclid=Cj0KCQjwzZj2BRDVARIsABs3l9INCKSJqHuFBta_jUTe8nPLj3FPQoo2jPZI5STds4r_ZbinIYhOznkaAgo2EALw_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

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?

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?

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.

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?

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.

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.

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?

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

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?

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/2025WE/clipsal-2025-double-power-point-gpo-10amp-250v-whi.html?gclid=CjwKCAjw8J32BRBCEiwApQEKgVMFM6I5arSg880KEbnNklXz6o239oNg_6uY4bxWCBdZ_khx7HiodRoCajwQA vD_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

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.

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-change-monitor-refresh-rate-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

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!

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.

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?

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.

Is your house wiring earthed?
I assume so, all the wall sockets are 3 pin
https://www.sparkydirect.com.au/p/2025WE/clipsal-2025-double-power-point-gpo-10amp-250v-whi.html?gclid=CjwKCAjw8J32BRBCEiwApQEKgVMFM6I5arSg880KEbnNklXz6o239oNg_6uY4bxWCBdZ_khx7HiodRoCajwQA vD_BwE

By the way, if your mains power sockets are switched, like the link you sent me, it's not sufficient just to turn off those switches. They will switch the line side of the power, but should not switch the neutral or safety earth connections. Even when the switch is off, those remaining connected wires may still provide a source of noise or a ground loop. Unplug means literally that.

- - - - -

Here in the states, at the local hardware store, we can buy a mains wiring tester.
https://www.amazon.com/Power-Gear-Receptacle-Indications-50542/dp/B002LZTKIA/din02c-20/din02c-20/din02c-20/din02c-20/din02c-20
It's roughly a 1.5" plastic cube, with three colored lights. Plug it into any mains socket, and the lights will tell you whether polarity is correct or reversed, and whether safety earth is present. They cost only a few dollars. Presumably a similar device is available where you live.

Your noise issue may end up relating to equipment grounding. (too soon yet to tell for sure) It wouldn't hurt to know for certain whether all your mains sockets are correctly wired and grounded. A tester like this would answer that question definitively.

I have been carrying one of those little cube AC line tested on live sound gigs for many moons. When noise rears it's ugly head I first check the outlets with that. If nothing can be done by using alternate outlets, out come the Sescom IL-19 ISO transformers (https://www.markertek.com/product/il-19/sescom-il-19-pro-audio-hum-eliminator-inline-with-isolation) which I never leave home without either.

Hi all,

I purchased this unit and tested all the powerpoints in the room
https://www.google.com.au/shopping/product/7037139878279783749?lsf=seller:100794174,store:14155113815528823343&prds=oid:14912125658364987733&q=bunnings+powerpoint+tester&hl=en&ei=rfrJXqaQJ-uD4-EP8YS1gAE&lsft=gclid:CjwKCAjwk6P2BRAIEiwAfVJ0rPGqd02qwDl5MktB0kxKq6sbRaTQ8Tni8TC8VpjjxkKpoA4fWSqXhBoCJJcQAvD_B wE,gclsrc:aw.ds

All powerpoints in the room tested OK


I then turned off and unpluged the powerpoints in the room and the surrounding 4 room. The Air cond was switched off at the breaker and the pool filter was unplugged. Lights & fridge were turned off

I then ran test 4
recorded a few sentences. paused at :43 unpluged the cable at the mike, waited 20 seconds, paused and unplugged the cable at the DBX

https://drive.google.com/open?id=1O36Kqwtq5tpMqGdv9U3JcMVcBk6YO897

Since I have no other XLR cables to test yet I replaced the USB cable and ran test 5, I could still hear the hum in the headphones but the recording seems slowed down and I'm not sure why.

https://drive.google.com/open?id=1PDQQDyQArhcSZ1zXoQ25g6Yf57xO5kZB

I need a cuppa tea & a lie down now

We've done OK on this one. The recording with the hum suddenly went quiet when you disconnected the microphone - so we have proven the DBX unit itself is silent, and the hum is entering the system before the XLR input on the DMX. Therefore the 'fault' is either the cable (likely) or the microphones (less likely), but you now need substitution. The cable as mentioned before must have all three conductors intact because the phantom power gets to the destination and we hear the audio. With all your kit turned off there should be no magnetic fields in the area from transformers, or other coil containing devices, unless the transformer in the DMX unit is the culprit.

We know you can't swap the mic cable or the mic - which would determine exactly if these are the issue, but if it's simply a poor screened cable - they exists - then moving the cable while recording - as in bringing it closer to the DMX will change the amount and character of the hum. So move the mic and cable around while recording silence and see if it changes - if it does, follow the hum volume, the closer you get to the offending item/area you will know from the sound.

Re: the pitch change, I suspect unplugging re-plugging fired the interface up in the wrong mode. You probably recorded in 48K and are replaying in 44.1K. Switching off and then on again should restore the usual defaults. It happens and is nothing to do with the cable.

The thing with cables is that screening is extremely variable in effectiveness. For years broadcasters shifted audio from centre to centre on twisted pair telecoms cable with no screening whatsoever, so it's a bit of a myth that it's critical, and balanced cables reduce hum - we think this means screening as a separate thing, but the balanced cables do most of the noise rejection, the screen just assists. Does your test meter do resistance? If there is leakage from hot or cold conductor to the screen, then the impact is on the phantom power voltage, but many mics are happy with wide phantom power voltage swings - 10-52Volts being enough to power the preamp in the mic, so a cable fault with leakage could allow the mic to energise and function, but the leakage could be enough to destroy the hum rejection. A new cable will sort this. Most faults are at the connectors, so if you can solder, cut 6" off each end and remake the connections. Swapping the mic often makes the hum go away, but does not automatically mean the humming mic is faulty - it may just react differently to cable faults.

I'm lucky enough to have trunks full of cable, and my oldest is the one that came with my first SM57 in the 70s, and that cable is still perfectly good, but over the years dozens have failed at the connectors. Perfectly normal. A simple joint gone dry, or a stray strand of screen that's touching pin 2 or 3 could be enough.

You're making progress, but now need to take action physically.

Paul, I completely agree with that assessment. And this is a very strange puzzle to solve! Different USB cable did not change a thing.

The attachment shows how much lower the noise is when the mic is unplugged.

What to try next? Turn on exactly the same kit, record silence, move the mic and cable around. Exactly as Paul Johnson suggested. Does the hum change in loudness or in character?

One other test would be to leave the cable connected to the mic. Unplug the cable from the dBx, plug it back into the M-Audio, and record another test (voice + silence) using the M-Audio. While recording the silence part of that test, turn the dBx power on and off, see whether the hum is related to the dBx being turned on (even 'though it's out of the circuit).

One almost gets the impression that there is a tiny source of audible hum in the booth which is actually being picked up by the mic ... a chorus of tiny mosquitoes with perfect pitch ... but of course the OP would have said "I hear the same hum in the booth, with my ears."

There's also the possibility of a corroded connector, putting more resistance in one side of the circuit than the other. This would probably be either the mic end of the cable, or the mic connector itself. Some good spray contact cleaner (Cramolin or Deoxit), Q-Tips, and pipe cleaners would identify that.

And there's a possibility that the power supply in the dBx is bad. Yet the recorded hum goes away when the mic is unplugged, so it's a very strange kind of fault.

Unfortunately, Paul (M), it looks as if you're in line for a few more tests. ;-) We have to be getting very close now. Good luck!