I'm running a Sennheiser MKH416P48 off the Zoom H4N and am getting some CRAZY interference, or something. I've noticed this in multiple locations, and have tried all that I know to get it to stop. I've changed the XLR, I've changed the batteries, and it still comes in and out, with not real consistency. Does this sound like an issue with the mic? My only other thought is to power the Zoom directly off of AC, to see if it's just a fluctuation in battery power, but I'm not sure if that's the problem. The mic has never been dropped, and has no damage that I know of to it. It's worked fine for years, and then, a few weeks ago, this. It's not location specific, as I've had it come in and out at different shoots. Any thoughts would be greatly appreciated.

Audacity shows this as a flat line, no sound.

Jim, I'm not sure what the problem is. I've opened the file with both Media Player Classic, and WinAmp, and both are showing wave forms and the sound that I'm talking about. Course, I open it with Media Player, and it doesn't play anything. Not sure what might be the problem. Anything I can change? Since it's working here, I'm not sure what to suggest.

I've installed Audacity, and also show a flat line, but there certainly is sound to it. I can hear both the hum of my laptop, and the high pitched interference. I'm not sure why there wouldn't be any wave form though, as the Zoom was set to 85 on the gain.

I don't hear anything on Widows Media Player either.

Not sure if this will help, but I've attached a blank screen to it and made it a video. If you still can't hear it, I'm just not sure what to do. It's working just fine here.

Only other thought as to why it might not be showing up for you is installed codec packs (K-lite) but I can't imagine why that would matter, as this file is straight from the Zoom.

Nope, no audio there either.

Well now, looks like I have two mysteries to figure out...

./sadface

I downloaded it and opened it in Cool Edit Pro. It is clearly an audio file, two channels, 48kHz sample rate, average peaks around -54dBFS, occasional peaks ~ 3dB higher than that.

I hear the room, and I hear a HF "birdie" wandering around the range from ~ 5kHz to ~ 6kHz, and it seems to have a harmonic an octave higher. You can even see a bit of the birdie here, on CEP's Frequency Analysis tool.

I feel pretty sure it's some sort of RF problem, but can't speculate as to the source. RF getting back into the audio, perhaps? It would be very hard to filter out of the received audio, because the frequency is very unstable. Is there anything else you can isolate? Unplug? Turn on/off?

(BTW, I can play the downloaded file just fine on Windoze Media Player... no problem whatsoever.)

Good luck!

Yeah, I shut down the computer and made it as quiet as possible in my office. The thing is, this has happened all over town, once in a diner, a couple of times in a residential area, and of course, here in my office on the university. As I have it turned on right now and am just listening to the audio in live preview mode, I barely hear it, at a very consistent, HF level. It comes and goes, which may be due to RF interference when something passes nearby, or in this case, my computer. It's just hard to tell because I can't seem to find what causes it, or when it starts, I don't know how to stop it. I'm mostly concerned with it being a problem with my microphone, as I hope it's not damaged.

Here's some room tone, very, very quiet obviously. I can't really tell if it's there right now, but I don't have Soundbooth in front of me here to do a frequency analysis.

Brian,

I had to turn my volume way up but I hear what sounds like a continuous whistling (for lack of a better word) almost like a teapot way far away.

It seems if you have someone talking over that it would be hardly noticeable. You want to hear line noise, you should hear some of my audio ;-} I'm getting better at it though.

Listen to a room with my eyes closed to see what may interfere with recording audio, and then try to remedy that.

Jonathan

Sometimes, it's not that bad, and voices do cover it up sometimes, but sometimes it's so loud that there's no way to actually avoid hearing it. In the past, I've gone in and isolated the frequency that it was buzzing in, and removed it, and it was alright. But it's when it fluctuates so wildly, that I just don't know what to do. The project I'm working on right now has a lot of quiet dialogue, and so, it doesn't hide anywhere. I'd just rather know if it's something local that I can seek out and turn off, or if something's gone wrong with the mic or the recorder. It sounds like, though, that it's interference from something other than those two, and that it's not something that I'm going to be able to avoid, which seems crazy to me, but if that's the case, that's the case. I'm not sure if a different sound capturing device, like say... Sound Devices 722 would somehow fix this, but I'm guessing it'd just make it 10x louder. Thanks!

Well, I think your best bet is process of elimination.

Do you have anything else plugged into the other input of the recorder? If so, unplug it.

Are you sure the mic cable is OK? Shielding OK?

Try the mic with a different recorder/mixer.

Try a different phantom mic with the existing recorder. Turn off the phantom power and try a dynamic mic. (Remember, this mic is a bit of an oddball, it uses RF demodulation to get the audio from the capsule, rather than DC bias voltage and a hi-z preamp.)

Try the recorder on AC power. (Maybe the phantom power supply in the recorder is acting up.)

Is the recorder's monitor level set extremely high? Possibly some coupling from the output to the input, from headphone cable to mic cable, etc.?

IMHO there's no good way to eliminate this noise in post, because there are at least two harmonics, and the frequency moves around quite a lot. Having voice "cover it" is not a solution. Downward expansion would drastically effect room tone, so that's not a good choice either.

Let us know how you make out with some substitution tests. Good luck!

I was finally able to hear it. I normalized the wav you posted in Soundtrack Pro and played on the good speakers. Kind of sounds like some of the noise you can get from a computer system or something with a bad capacitor. Doesn't sound to me so much like RF noise.

Problem solving would dictate changing out things one at a time so you can isolate the issue. Doesn't sound like you swapped out the mic yet. If you can get another mic and try to see if the problem is the mic. I have had 416's need to be repaired by Sennheiser. Usually a bad ground path which gradually degraded the mic sound so you may be in the early stages of a mic problem.Pretty reasonable and fast turnaround time last I dealt with them. If it is not the mic or the cable then it may be the recorder. Any part the chain can be a problem. Good Luck

I don't have the time to listen at the mo.

BUT

Is your mobile phone switched on?

Have you checked the cable and swapped out the cable?

It could be the recorder input that is susceptible to stray RF.

I now use Neutrik EMC XLRs on my cables to keep out RF.

I hope this helps.

I hear it. The Sennheiser MKH 416 is an RF condenser microphone. I'm guessing that, since you have had it a long time, part of the rf circuitry may be out of alignment due to aging parts, most likely a capacitor.

A trip back to the mothership for a tweek should improve things.

Regards,

Ty Ford

Thank you all for your thoughts. Here's what I've tested so far:

1) I've tried different XLRs, one older, one brand new, both seem to have the same result.
2) I've tried it with two different Zoom H4Ns, both have the same problem.
3) I've tried in several different locations, sometimes I can hear it, sometimes I can't.

4) Maybe I'm crazy, but I pulled the XLR out of the Zooms, but left my headphones plugged in. I feel like I can still hear the noise. This, interesting as it is, appears to be coming through on both Zooms, even without a mic plugged in, so I'm thinking it's not the mic. It's the Zoom, and it's picking up something. I'm going to attach the file from both Zooms recording audio, with no XLR plugged in. You can certainly hear the noise, even though there's no mic plugged in. It's certainly stronger on my Zoom than it is the borrowed one, but that's probably because mine has taken at least one spill.

I have not tried another mic yet. Thoughts? Anyone with a Zoom have this problem? A setting I'm just screwing up? The one thing I haven't yet tried that I forgot until just now is trying the AC cord for the Zoom, plugging into the wall, to see if it's just batteries failing to power it adequately.

For reference, ZoomA is my Zoom, and ZoomB is the borrowed one.

This was a very useful test! In Zoom A, the "birdie" is there, but different from the original stereo file. The original file had a fundamental around 5- 6kHz, plus a harmonic an octave higher. The new Zoom A file has just one noise frequency, around 8- 9kHz. The Zoom B file has no such "birdie," just typical background hiss.

This test clearly rules out a problem with the mic, and seems to indicate the problem is only in your Zoom. We need to know, for certain, whether phantom powering was turned on or off in Zoom B.

The fact that Zoom A has the noise without any mic suggests that it's either an internal issue with that recorder, or some sort of coupling/oscillation between the output (earphones cable) and input (due perhaps to proximity to the mic jack). If I had to bet, I'd vote for the former.

Remember that the Zoom has some sort of internal oscillator (and step-up transformer, rectifier, and filtering) to boost its battery voltage up to 48V for phantom powering. You could be hearing this oscillator running. That's why I said (above) that we need to know whether phantom was turned on or off when you recorded the Zoom B file.

I strongly suggest again three tests which I suggested in my post yesterday, which you apparently have not yet tried:

Turn off the phantom power and try a dynamic mic. {snip}

Try the recorder on AC power. (Maybe the phantom power supply in the recorder is acting up.)

Is the recorder's monitor level set extremely high? Possibly some coupling from the output to the input, from headphone cable to mic cable, etc.?

If you would run all the tests, it would be fairly simple to isolate the source of the problem logically.

Obviously you want to run those tests on Zoom A, since that's the one with the birdie.

And, if phantom was off when you recorded the Zoom B file, turn it on and record another file from Zoom B. (And please use new file names for all the tests.)

Thank you all for your thoughts. Here's what I've tested so far:

1) I've tried different XLRs, one older, one brand new, both seem to have the same result.
2) I've tried it with two different Zoom H4Ns, both have the same problem.
3) I've tried in several different locations, sometimes I can hear it, sometimes I can't.

4) Maybe I'm crazy, but I pulled the XLR out of the Zooms, but left my headphones plugged in. I feel like I can still hear the noise. This, interesting as it is, appears to be coming through on both Zooms, even without a mic plugged in, so I'm thinking it's not the mic. It's the Zoom, and it's picking up something. I'm going to attach the file from both Zooms recording audio, with no XLR plugged in. You can certainly hear the noise, even though there's no mic plugged in. It's certainly stronger on my Zoom than it is the borrowed one, but that's probably because mine has taken at least one spill.


Almost any improperly terminated input will act as a radio receiver. If teh 416 does the same thing when plugged into something else. It's the mic.

Regards,

Ty Ford

Turn off the phantom power and try a dynamic mic. {snip}

Try the recorder on AC power. (Maybe the phantom power supply in the recorder is acting up.)

Is the recorder's monitor level set extremely high? Possibly some coupling from the output to the input, from headphone cable to mic cable, etc.?

I turned off the phantom power and tried a Shure SM57, which I'll attach.

I used the AC, also attached, but with no mic plugged in

Lastly, I've turned the gain down, and didn't really hear any difference in anything.

Course, right now, I'm not hearing the same kind of interference as I was before, so ... ugh.

The last thing that I think it could be is the headphone jack. It's extremely loose, from what I imagine was someone pulling the headphones out at great force, sideways. I'm going to open up the Zoom, and see what kind of damage has been done, if I am able to see any at all. It very well could be that there's something jacked (heh) up in there, and that there's a short occurring. Though it seems to me that it would be consistent... maybe not?

Well, doesn't look like my tiny screwdriver will be able to fit, so that's an 86 on opening up the Zoom. Just note that that problem exists.

Looking at the zoom a file, not only does a spectral display show the 9K trace pattern, but every three to four seconds there is a dip in the noise, but a slight increase in the noise frequency. I've no idea what this means but I can't say I have ever seen this before. It suggests that maybe we're looking at some DC component that is charging/discharging. Just a thought. Where is the phantom power coming from? Internal from the recorder?

In the original files, the phantom power is coming directly from the Zoom, which is powered by two AA batteries. In the most recent files, the Zoom was powered by an AC adapter plugged into the wall. The microphone on the original file was a Sennheiser 416P48. The middle files were without a microphone at all, but still picked up the problem; the final files attached were from a Shure microphone, with the phantom power in the zoom turned off.

Brian:

Thanks for the additional test data!

In the most recent two files (Shure and AC) the birdie is not present.

Question: Was the phantom power turned on or off for the "AC-powered" test? Off, correct?

In addition to answering that question, run one more test, again AC powered. But change the state of phantom power. (In other words, if it was ON in the previous "AC-powered" test, turn it off; if it was OFF in the previous "AC-powered" test, turn it on.) Keep everything else (gain, etc.) the same.

Name that file something like "AC-powered-phantom-ON" or OFF as the case may be. And post that file.

At this point, I'm suspecting the phantom power supply in the recorder, perhaps one more test will help clarify things.

Looking at the zoom a file, not only does a spectral display show the 9K trace pattern, but every three to four seconds there is a dip in the noise, but a slight increase in the noise frequency.
That's not quite how I would describe the ZoomA file.

I don't see any dip in the noise level.

Looking at the frequency, I see a slow, gradually rising curve, with some irregularities.

At 2.8 sec., and again at 5.6 sec., the frequency appears briefly to jump above the gradual curve. There is a bigger frequency jump from 8.5 to 8.8 sec. After that, the base frequency starts to waver up and down a bit, with two more brief upward spikes around 11.3 sec and 14.2 sec.

As I've said elsewhere, I'm beginning to suspect the internal oscillator which boosts the supply voltage to the voltage needed for phantom powering. We may be seeing the actual oscillator frequency, or perhaps we're seeing an alias produced between the oscillator and the sampling frequency.

(Click the thumbnail and a slightly larger version will pop up.
Then click the popup to see the original capture size, so you can see all the detail.)

I think this may troubleshoot what the problem is. You'll see 4 files below. I tested the Zoom, with no mic plugged in:

1) Phantom power using batteries
2) Phantom power using AC
3) No phantom power using batteries
4) No phantom power using AC.

Brian:

That's an excellent very complete set of tests! Thanks for taking the time.

No phantom / AC does NOT have the birdie.
No phantom / batteries does NOT have the birdie.
Phantom / AC does NOT have the birdie.
Phantom / batteries DOES have the birdie!

From this, I would conclude that the HF birdie is, in fact, coming from the oscillator which generates the phantom supply power. And, for some reason, it is present only when running on battery power.

It remains to be seen whether the ~ 8kHz frequency is the actual oscillator frequency, or whether it's an alias from the sampling rate. We can investigate that later if that's of any interest. (Indeed, the frequency might change, or the birdie might disappear, at a different sampling rate.) Let's ignore that for now.

Now that we've identified the source of the problem, let's try one more test which will have some practical ramifications. Remember that the birdie was worse, and lower in frequency, with the mic connected.

Plug in the condensor mic again, turn on phantom power, and make two more files: one on battery, one on AC. If we're lucky, the birdie will be absent from the AC-powered recording, even with the mic connected.

Hi

Just to add it does sound like a DC to DC or AC converter creating the noise, such a beast will be needed to provide the 48volt. These will change their switching frequency to regulate the output so will drift and jump around, for example as the batteries weaken or the load varies the frequency will shift. They are also a known cause of EMI/RFI.

Regards

Phil

Brian:
Plug in the condensor mic again, turn on phantom power, and make two more files: one on battery, one on AC. If we're lucky, the birdie will be absent from the AC-powered recording, even with the mic connected.

Some inconsistent test results, but could have just been... hell I have no idea what it could have been, but here's what I've got.

Man, that is shocking!

I did expect to hear some sort of oscillation with the phantom/mic combination, simply because that's what was bothering you in the first place.

I rather expected it to occur with battery power, because that's when we heard it with no mic connected; but in fact your battery file was clean. Very odd, because that's when you had the initial problem.

I can't say I was surprised that the AC power file was clean, because it was clean with no mic.

But I was blown away to hear the low frequency really ugly oscillation in the "AC2" test. Of course the phantom power is on, and that's when we expected trouble. But AC with no mic was quiet; why did AC with mic turn out to be the worst of all the tests?

And why the discrepancy between AC(#1) and AC2? Were there any variables whatsoever between AC(#1) and AC2? Different mic position? Different situation in the room? Different anything that you can think of?

What's the headphone situation when you run the tests? Any phones plugged in, or not? What's the monitor gain setting? Where is the headphone cable (if any) relative to the mic jack and mic cable (if any)? {This is a long shot, in case it might be some strange feedback or crosstalk. In reality, I think it's the phantom power supply. But I guess the PS oscillator might be leaking out on the headphone jack... anything is possible.}

If you borrow the other Zoom again, and repeat at least these last few tests on that recorder, it might help to narrow this down, as to whether it's typical of this model, or just a glitch with your particular machine. (It's going to get confusing keeping track of all the variables and all the test results. Sigh.)