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Canon C100 Audio distortion, amplified camera noise (Ch 1), and +48V noise

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Rick James
Canon C100 Audio distortion, amplified camera noise (Ch 1), and +48V noise
on Nov 17, 2016 at 9:42:58 pm
Last Edited By Rick James on Nov 17, 2016 at 11:43:38 pm

My company has been struggling with multiple audio issues on 2 Canon EOS C100 (mark one) cameras. Camera A has the Dual Pixel Auto Focus update and is running firmware 2.0.7.1.00. Camera B does not have the autofocus update and has firmware 1.0.7.1.00 installed.

Here is a



illustrating the different noise issues. The camera’s have 3 audio issues listed bellow:

1. Unknown distortion on XLR input channel 1 when an external mic is attached (in the top handle grip unit). Sounds like overload, over modulation, clipping (but the audio levels are within good range).

2. When either input is switched to Mic +48 phantom power, there is a constant buzz accompanied by a high-rpm “beating or thumping" sound. The noise only appears when +48 is selected and is heard even when nothing is connected to the XLR inputs.

3. XLR input Chanel 1 presents a “white noise/hiss” sound similar to the common noises produced by a cameras internal mechanisms, only louder. Assuming it is camera noise, it is also present in Channel 2 at a lower level.

HISTORY
Cameras were purchased in late 2014 or early 2015.
Sony microphones from older sony DVCam/miniDVcam’s have been used as the on-camera mic (Sony ECM-NV1 and ECM-MX1)

Distortion in Channel 1 Input appeared in each camera after a firmware update was installed (details unknown).
The +48V buzz in both inputs and the loud white noise/hiss in channel 1 appeared intermittently at first, and gradually became constant (is constant now).

Attempted solutions have included camera reset (using menu option and reset button), update to latest firmware, reinstalling firmware (camera would not accept), using several different combinations of mic’s and XLR cables, trying different audio settings.

Camera’s mic input (3.5 mm plug) works well with no issues. The issues are only with the XLR inputs in the top handle unit.


TEST SETUP
3 different XLR cables used: 6’ low noise balanced *with polarity reversed, 25’ balanced Kopul 3000 Noiseless, 18” balanced Kopul 3000 Noiseless.

7 different microphones used: Sennheiser ME66/K6 super cardio condenser, Audio Technica AT897, Shure SM87A condenser mic, Sony ECM-NV1 and XM1 (from older Sony Cameras), Sennheiser G3 wireless Lav, Sony UWP wireless Lav.


FINDINGS
There is NO DISTORTION when the Shure SM87A mic is connected to Channel 1 with any of the XLR cables, (+48V was turned on in the camera). The +48V buzz and the white noise is still present.

There is NO DISTORTION when the Sony ECM-NV1 connected to Channel 1 with the reverse polarity cable. (+48V was turned on in the camera).

There is NO +48V BUZZ when the Sony ECM-XM1 is connected to Channel 1 or 2 with a balanced XLR cable. (+48V was turned on in the camera).

All other combinations presented the distortion, buzz, and white noise.


CONCLUSION

We need to fix the C100 mic inputs and we also need to figure out what is causing these problems. My understanding of audio signals and electronic circuits is pretty basic but after researching the issues, it seems like there are a combination of possible factors. It seems likely that components inside the preamps in both cameras have become damaged over time. Could this be a result of frequently plugging in powered microphones into the XLR terminal when phantom power was active, or by a combination of activity like misfired cables? AND/OR the usage of the Sony ECM microphones over time possibly reversed the polarity of the C100’s preamps? The Shure SM87A did not present the Channel 1 distortion. I know that most microphones guard against unbalanced cables, etc., but many Shure mic’s add additional protection against voltage fluctuations, reverse voltage, and misswired cables/equipment through a variety of protection diodes and decoupling capacitors that aren’t included in other microphones. The Sony mic’s are wired with their copper shielding split between pin 1 and chassis ground, whereas the XLR cables are only wired to pin 1. Not sure if this has any relevance.

If anyone has suggestions or possible solutions let me know.

Thanks!


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Ty Ford
Re: Canon C100 Audio distortion, amplified camera noise (Ch 1), and +48V noise
on Nov 18, 2016 at 4:48:35 pm

Hello Rick and welcome to the Cow Audio Forum,


We need to fix the C100 mic inputs and we also need to figure out what is causing these problems. My understanding of audio signals and electronic circuits is pretty basic but after researching the issues, it seems like there are a combination of possible factors. It seems likely that components inside the preamps in both cameras have become damaged over time. Could this be a result of frequently plugging in powered microphones into the XLR terminal when phantom power was active, or by a combination of activity like misfired cables?

Not so much by plugging in. Bad cables, yes.

AND/OR the usage of the Sony ECM microphones over time possibly reversed the polarity of the C100’s preamps?

Not possible. ?

The Shure SM87A did not present the Channel 1 distortion. I know that most microphones guard against unbalanced cables, etc., but many Shure mic’s add additional protection against voltage fluctuations, reverse voltage, and misswired cables/equipment through a variety of protection diodes and decoupling capacitors that aren’t included in other microphones.

Mics typically don't require protection circuitry. Condenser mics do need to have circuitry that properly applies the incoming Phantom Power.

The Sony mic’s are wired with their copper shielding split between pin 1 and chassis ground, whereas the XLR cables are only wired to pin 1. Not sure if this has any relevance.

Preamps may be designed in a variety of ways. Usually pin 1 to ground is fine. What the preamp wants to see is another thing. That may or may not be a point worth inspecting and experimenting with.

If anyone has suggestions or possible solutions let me know.

Any mic preamp with no mic attached will probably be noisy because the circuit is not terminated (by a mic).

Different mics have different amounts of selfnoise , normally heard as hiss. As a rule, the smaller the diaphragm, the more the hiss.
Lavs, therefore, hiss more than the SM87A.

Using battery powered mics with both battery power and phantom power turned on may create a conflict, resulting with noise and heated batteries. Usually, use either batter or phantom.

-------------

There is NO DISTORTION when the Shure SM87A mic is connected to Channel 1 with any of the XLR cables, (+48V was turned on in the camera). The +48V buzz and the white noise is still present.

Are you monitoring each channel separately? Is the buzz and noise on both channels or in the unterminated channel 2?

When you find a mic/cable that works, keep the cable plugged into the camera and attach different mics to it to see how each one does. Also plug a mic and cable into inout 2 to properly terminate it.

There may be some menu items in the C100 that need to be changed. I don't know the camera that well, but I think I recall its menu structure is not that obvious.

Regards,

Ty Ford
Cow Audio Forum Leader

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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Rick James
Re: Canon C100 Audio distortion, amplified camera noise (Ch 1), and +48V noise
on Nov 18, 2016 at 8:37:54 pm

Hello Ty,

Thank you for taking the time to read my post and for your response. Btw this was my "first time poster, long time reader" post and I've read many helpful threads that included your posts over the years so I appreciate any input you and the community can offer.

Regarding your questions:
(RJ)...There is NO DISTORTION when the Shure SM87A mic is connected to Channel 1 with any of the XLR cables, (+48V was turned on in the camera). The +48V buzz and the white noise is still present.
(Ty)Are you monitoring each channel separately? Is the buzz and noise on both channels or in the unterminated channel 2?
Each channel was monitored separately and individually. The Buzz is heard on both channels. The white noise/static is heard in channel 1. It sounds like the normal camera noise and mic noise is being amplified in channel 1, while in channel 2 it is normal.
(Ty)When you find a mic/cable that works, keep the cable plugged into the camera and attach different mics to it to see how each one does. Also plug a mic and cable into inout 2 to properly terminate it.

I did this in the initial test but I tried it again to verify the results and they remain unchanged. However, I did find something that I did not notice before. Initially I found that the +48V buzz is not present in either channel when the Sony ECM-XM1 is connected to the camera with an XLR extension cable (it is present when plugged directly into the camera). The buzz is there with or without an extension in either channel with the Sony ECM-NV1. When I have both mic's plugged in with an XLR extension cable, I hear the +48V buzz in whichever channel the NV1 is going to. If I send +48V to the NV1 with no phantom power going to the other mic, the level of the buzz is softer. Then when I send phantom power to the other channel, the buzz gets louder in whichever channel the NV1 is plugged into but there is still no buzz in the XM1. So, XM1 to Ch1 or 2 = BUZZ. XM1 + extension to Ch or 2 = NO BUZZ. NV1 +/- extension to Ch1 or 2 = BUZZ. NV1 +/- extension to Ch 1 or 2 AND +48V on Ch 1 & 2 = LOUDER BUZZ in NV1 but NO BUZZ in XM1.

The C100's did not come with an external mic so we used a couple the Sony mic's mentioned above. They were originally on a PD-170 and an HVR-Z7 or something similar. I'm not sure if this is useful information, but here are the only XLR input specs I could find for each of these cameras:
C100: XLR jack (pin1: shield, pin2: hot, pin3: cold), 2 sets. Sensitivity MIC setting: -60 dBu (manual volume center, full scale -18 dB) / 600
Ω LINE setting: 4 dBu (manual volume center, full scale -18 dB) / 10 k Microphone attenuator: 20 dB
HRV-Z7 (w/XM1 mic): XLR 3-pin, female, -48 dBu: 3kΩ (kilohms) +4 dBu: 10kΩ (kilohms) (0 dBu=0.775 Vrms)
PD-170 (w/NV1 mic): 3-pin female x 2, 327 mV, -60 dBu, 3 k Ω , +4 dBu, 10 k Ω (0 dBu = 0.775 Vrms)

(Ty)There may be some menu items in the C100 that need to be changed. I don't know the camera that well, but I think I recall its menu structure is not that obvious.

I've tried many combinations of settings but none that I've found takes any of the issues away. Here are the usual settings:

I've searched pages and pages of google using countless keyword combinations trying to find anything resembling similarity to the issues I described and I did read about a lot of folks who have had noise issues when using Sony wireless lav's like the UWP system with their C100's (both Mk I and Mk II). The buzz/static signal they describe sounds much like the +48V buzz we have, but our buzz isn't limited to only Sony wireless, it is present on any phantom powered mic and it is present when phantom power is turned on with no mic connected (I turned +48V on without termination only as an experiment, this is not a common practice). The solution they found was replacing the transmitter's sony cable with a Sennheiser cable. This solution didn't work for me on our Sony lav's.

One more thing worth mentioning is that a 2013 firmware update for the C100 included modifying the XLR terminal polarity. I wasn't with the company when the cameras were purchased or when the audio issues started and my coworkers have different views of when the audio issues started or if/when/which firmware updates were installed. From Canon firmware update 1.0.1.1.00:
The polarity balance of the XLR terminal has been modified to improve compatibility with external audio devices. The pin configuration has been modified to be consistent with the Instruction Manual. Before the Firmware update the pin configuration for the XLR jack was (pin1: shield, pin2: cold, pin3: hot). After the Firmware update the pin configuration for the XLR jack will be (pin1: shield, pin2: hot, pin3: cold). The XLR pin configuration meets the international AES standard recommendation. The firmware update will avoid the scenario where the unit if used in combination with a device of differing polarity of the XLR terminals, would result in weakened sound levels due to a reversal of the phase relationship.

This statement as well as the folks with the Sony lav noise issues, plus a couple of articles including this one: Phantom power could damage some microphone preamps as well (notably the second to last paragraph) is what made me wonder if this is a progressive issue that happened over time - not necessarily from one single issue. Whatever happened, it happened to both cameras around the same time. I don't know much about the history of the cameras or if they ever had a line feed at the same event, etc.

I figure we'll either send these in to Canon or replace the handle units but it would be nice to identify the problem and figure out what could have caused it so we don't damage replacements.


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Ty Ford
Re: Canon C100 Audio distortion, amplified camera noise (Ch 1), and +48V noise
on Nov 18, 2016 at 10:22:37 pm

::SIGH::

I thought RED were the only camera people who reversed polarity on their inputs out of stupidity.

I don't think you'll damage any replacements.

There may be something wrong with the camera inputs. Turning on Phantom Power shouldn't create any noise in and of itself.

I'd send the camera(s) in and see what they find.

Regards,

Ty Ford
Cow Audio Forum Leader

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide
Ty Ford Blog: Ty Ford's Blog


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Rick James
Re: Canon C100 Audio distortion, amplified camera noise (Ch 1), and +48V noise
on Nov 19, 2016 at 2:25:36 am

Thanks Ty. That seems to be the consensus even with the local Canon Certified tech who does "minor" repairs. If I find anything interesting I'll post it here for anyone who stumbles upon this.

Cheers


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huy mach
Re: Canon C100 Audio distortion, amplified camera noise (Ch 1), and +48V noise
on Jul 6, 2017 at 7:57:25 pm

SOLUTION FOUND!!

Hi everyone. After an extensive and exhausted search for the solution, I think I found one that works perfectly for me (maybe not for everyone).

Camera: Canon c100 MkII
Wireless mic: Sony UTX-B03 transmitter, URX P03 receiver
Connect: XLR

The problem: scratchy-static-digital-interference type noise that would not go away no matter the setting configuration on the microphone or camera. I even called Sony, B&H, and Canon customer service. B&H sent me replacement XLR cables of a different brand, but the problem persisted.

The solution: shooting at AVDHD 59.94p (instead of 29.97)
This helps me in two ways - I like shooting with a higher frame rate to get some slow-motion, and also it solved my noise issue!
I know not everyone likes to shoot at that high of a frame rate, but it works perfectly for me.

in the c100 MKII camera settings:

Menu > Other functions >AVCHD > Bit Rate > 28 Mbps LPCM

I hope this helps someone out there.


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