Interference? What is that? - Page 2 at DVinfo.net

Go Back   DV Info Net > The Tools of DV and HD Production > All Things Audio

All Things Audio
Everything Audio, from acquisition to postproduction.


Reply
 
Thread Tools Search this Thread
Old February 9th, 2012, 05:38 PM   #16
Trustee
 
Join Date: Jan 2006
Location: New York, NY
Posts: 1,267
Re: Interference? What is that?

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
Daniel Epstein is offline   Reply With Quote
Old February 10th, 2012, 02:18 AM   #17
Major Player
 
Join Date: Oct 2008
Location: Oxfordshire, UK
Posts: 974
Re: Interference? What is that?

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.
__________________
John Willett - Sound-Link ProAudio and Circle Sound Services
President: Fédération Internationale des Chasseurs de Sons
John Willett is offline   Reply With Quote
Old February 10th, 2012, 07:22 AM   #18
Inner Circle
 
Join Date: Nov 2004
Location: Baltimore, MD USA
Posts: 2,323
Re: Interference? What is that?

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
Ty Ford is offline   Reply With Quote
Old February 10th, 2012, 08:56 AM   #19
Major Player
 
Join Date: Aug 2008
Location: Columbia, Missouri
Posts: 210
Re: Interference? What is that?

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.
Attached Files
File Type: wav ZoomA.wav (2.75 MB, 30 views)
File Type: wav ZoomB.wav (2.00 MB, 18 views)
__________________
"Make the most of yourself, for that is all there is of you." R W Emerson
RED ONE MX | 5DmkIII | SD744T | SD442 | Sennheiser MKH416 P48
Brian Maurer is offline   Reply With Quote
Old February 10th, 2012, 09:23 AM   #20
Trustee
 
Join Date: Jan 2011
Location: Pennsylvania
Posts: 1,359
Re: Interference? What is that?

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:

Quote:
Originally Posted by Greg Miller
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.)

Last edited by Greg Miller; February 10th, 2012 at 09:54 AM.
Greg Miller is offline   Reply With Quote
Old February 10th, 2012, 10:13 AM   #21
Inner Circle
 
Join Date: Nov 2004
Location: Baltimore, MD USA
Posts: 2,323
Re: Interference? What is that?

Quote:
Originally Posted by Brian Maurer View Post
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
Ty Ford is offline   Reply With Quote
Old February 10th, 2012, 01:40 PM   #22
Major Player
 
Join Date: Aug 2008
Location: Columbia, Missouri
Posts: 210
Re: Interference? What is that?

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?
Attached Files
File Type: wav Shure.wav (2.79 MB, 21 views)
File Type: wav Ac-powered.wav (2.80 MB, 28 views)
__________________
"Make the most of yourself, for that is all there is of you." R W Emerson
RED ONE MX | 5DmkIII | SD744T | SD442 | Sennheiser MKH416 P48
Brian Maurer is offline   Reply With Quote
Old February 10th, 2012, 01:45 PM   #23
Major Player
 
Join Date: Aug 2008
Location: Columbia, Missouri
Posts: 210
Re: Interference? What is that?

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.
__________________
"Make the most of yourself, for that is all there is of you." R W Emerson
RED ONE MX | 5DmkIII | SD744T | SD442 | Sennheiser MKH416 P48
Brian Maurer is offline   Reply With Quote
Old February 10th, 2012, 02:45 PM   #24
Inner Circle
 
Join Date: Nov 2005
Location: LOWESTOFT - UK
Posts: 2,125
Re: Interference? What is that?

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?
Paul R Johnson is offline   Reply With Quote
Old February 10th, 2012, 02:52 PM   #25
Major Player
 
Join Date: Aug 2008
Location: Columbia, Missouri
Posts: 210
Re: Interference? What is that?

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.
__________________
"Make the most of yourself, for that is all there is of you." R W Emerson
RED ONE MX | 5DmkIII | SD744T | SD442 | Sennheiser MKH416 P48
Brian Maurer is offline   Reply With Quote
Old February 10th, 2012, 11:56 PM   #26
Trustee
 
Join Date: Jan 2011
Location: Pennsylvania
Posts: 1,359
Re: Interference? What is that?

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.

Last edited by Greg Miller; February 11th, 2012 at 06:01 AM.
Greg Miller is offline   Reply With Quote
Old February 11th, 2012, 06:30 AM   #27
Trustee
 
Join Date: Jan 2011
Location: Pennsylvania
Posts: 1,359
Re: Interference? What is that?

Quote:
Originally Posted by Paul R Johnson View Post
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.)
Attached Thumbnails
Interference? What is that?-zooma-spectral.jpg  

Last edited by Greg Miller; February 11th, 2012 at 09:43 AM.
Greg Miller is offline   Reply With Quote
Old February 11th, 2012, 09:45 AM   #28
Major Player
 
Join Date: Aug 2008
Location: Columbia, Missouri
Posts: 210
Re: Interference? What is that?

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.
Attached Files
File Type: wav No Phantom and AC.wav (2.79 MB, 25 views)
File Type: wav No Phantom and Batteries.wav (2.82 MB, 27 views)
File Type: wav Phantom and AC.wav (2.82 MB, 29 views)
File Type: wav Phantom and Batteries.wav (2.81 MB, 27 views)
__________________
"Make the most of yourself, for that is all there is of you." R W Emerson
RED ONE MX | 5DmkIII | SD744T | SD442 | Sennheiser MKH416 P48
Brian Maurer is offline   Reply With Quote
Old February 11th, 2012, 10:22 AM   #29
Trustee
 
Join Date: Jan 2011
Location: Pennsylvania
Posts: 1,359
Re: Interference? What is that?

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.
Greg Miller is offline   Reply With Quote
Old February 11th, 2012, 11:46 AM   #30
Major Player
 
Join Date: Feb 2010
Location: London
Posts: 302
Re: Interference? What is that?

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
Phil Lee is offline   Reply
Reply

DV Info Net refers all where-to-buy and where-to-rent questions exclusively to these trusted full line dealers and rental houses...

Professional Video
(800) 833-4801
Portland, OR

B&H Photo Video
(866) 521-7381
New York, NY

Z.G.C.
(973) 335-4460
Mountain Lakes, NJ

Abel Cine Tech
(888) 700-4416
N.Y. NY & L.A. CA

Precision Camera
(800) 677-1023
Austin, TX

DV Info Net also encourages you to support local businesses and buy from an authorized dealer in your neighborhood.
  You are here: DV Info Net > The Tools of DV and HD Production > All Things Audio

Thread Tools Search this Thread
Search this Thread:

Advanced Search

 



Google
 

All times are GMT -6. The time now is 01:37 PM.


DV Info Net -- Real Names, Real People, Real Info!
1998-2017 The Digital Video Information Network