PDX10 Audio Hum through XLR mount at DVinfo.net

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Sony TRV950 / PDX10 Companion
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Old March 28th, 2004, 10:55 PM   #1
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PDX10 Audio Hum through XLR mount

Hunted through the many other threads on Audio/Mics in this forum and haven't come across anything on this topic yet.

Could people please comment or make suggestions.

I have done a fair amount of experimenting with the xlr ECM-NV1 mic. Using Sennheiser headphones for tests.

While the mike is mounted on the XLR mount there is hum coming through at a reasonable level (I'm not reffering to hiss discussed in another thread in this forum). When the mic is off the mount (hand held) - no hum. When the PDX10 turns off the standby mode and the motor turns off - no hum. (This hum sounds a bit like the 240volt hum you get in amps)

The hum is the on the recorded tape, not there when hand held.

Sometimes I am using a second shotgun mic at the same time. (made up a neat mount to slip into the flash shoe on top of the xlr mount) This microphone - JVC M-510 picks up about 50% less hum mounted, none handheld. The JVC is metal rather than plastic - may help, also two and a half times longer and has its own battery therefore not needing the phantom power. The two mics together are for shotgun stereo effects (long story)

Has anyone else encountered this, any solutions?
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Old March 29th, 2004, 01:26 AM   #2
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A better shockmount for more distance and separation?
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Old March 30th, 2004, 06:21 PM   #3
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It does sound a bit mechanical if it goes away when the motor shuts down. Then again, could be noisy contacts on the drum motor. Minor arcing and producing a low level but steady static that could be hum.

Might also simply be the actual motor noise or the cassette reel noise.

Have you eliminated those as posibilities?

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Old April 3rd, 2004, 10:52 AM   #4
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Try turning on the camera's NR circuit. Does a great job of doing away with motor noise even when using the consumer stereo mic array that's built into the lower front of the camera.

MENU / cassete icon / MIC NR / ON
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Old April 6th, 2004, 04:10 AM   #5
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Ok, I just checked on my PDX10.

Yes, I get the hum and I get the hiss (when either the volume or mic levels are brought up to more than halfway).

That is really unfortunate. When I turn mic NR off, then there is an additional hum.

On top of that, when you walk with the camera and the rubber XLR mic mount bounces up and down, the mic pics it up.

It is definately an in camera sound. Some of it is the motor even.

If you leave it the levels for mic or xlr on auto, you'll hear it.

Does anyone find this to be a problem when trying to get clean sound for dialogue?

The only two solutions I can think of are to use a boom pole and physically put the mic farther away from the camera (which unfortunately means not on camera) and/or use a wireless mic.

Perhaps we if left the mic levels low enough, we won't get as much hum?
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Old April 6th, 2004, 12:20 PM   #6
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It is normal on many sony cams to get better signal to noise ratio when level is set to manual because of the way the AGC is wired into one of the chips. Although Sony has made this better over the years it might be possible to make it even better by modifying the circuit. Should not be necessary on the PDX10 though, for me the S/N ratio is quite acceptable, even in conditions like that which you describe, so it is still possible that there is something wrong with your camera and noise is higher than it should be... if I were you I would go to the store and compare with another PDX10, then you will know if you need better mics or need to send the camera back for service.

If the camera is not malfunctioning then you might get marginally better results by installing a higher quality camera-mounted microphone and a better shock mount, but I think that amount of money would be much better spent on boom or lav kits, or both. A camera-mounted mic is not really suitable for serious dialogue work the way you seem to be trying to use it. A good quality wireless lav kit is expensive but can save you headaches. A boom mic is a good idea but of course you will need a boom operator. The only way the on-cam mic will get the job done is if the subject has a loud voice, there is little ambient noise, the camera doesn't move much, there is no wind and you are less than 2 meters away from the subject... all these conditions are seldom met.

Check the cam, make sure it's audio circuit and the mic are ok. Then, spend some money on a good lav kit, Sony's is nice, I use one with an omni capsule. If you can't afford the lav, buy a boom and a better mic with a good shock mount, so you can mount the mic on the camera for a somewhat better sound or mount it on the boom when you can have a boom operator to help.
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Old April 7th, 2004, 07:47 AM   #7
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Also take a look at what your LCD viewfinder brightness is set at. Try reducing the brightness if you are hearing more noise with this open. There is a history of issues with the LCD brightness causing a buzz in the audio for Sony.

Also, when you go over the 50% mark on most audio systems, you are adding level by increasing the gain of the circuits. Some circuits are inherently noisy in their design. In Auto you may notice the hiss creeping in slowly after a loud noise. I sometimes hear this same thing on CD releases of older music.

If you can, avoid increasing the levels past that halfway mark by perhaps inserting a small mixer with good noise characteristics ahead of the camera and use Line Level input to the camera. You can have the gain in the quieter mixer circuits and still get enough sound to work with.

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Old April 8th, 2004, 01:31 PM   #8
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Ronald is this the problem you have?

http://www.dvinfo.net/conf/showthread.php?s=&threadid=23058

It sounds similar to the problem I have where you get no noise if you leave the XLR set to AUTO but gets tons of buzz if you change it to MANUAL.

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Old April 8th, 2004, 11:19 PM   #9
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Sorry the wording in my previous post was the wrong way around so it may have lead to some misunderstanding. I apologize. It should have said: 'It is normal on many sony cams to get better signal to noise ratio when level is set to automatic because of the way the gain control is wired to one of the chips'.

Sony issued a bulletin about this problem (on the PD150) and recommends that you stick with auto gain control and use manual only when levels are very high. Applying gain using the manual control can result in more noise than letting the camera automatically increase gain when incoming audio is weak.

There is another audio noise problem with the 950 related to the LCD circuitry inducing noise when screen brightness is set to the lower level. This can also happen on some portable computers. It seems that the way to lower the brightness of the LCD's lamp is to flicker it at a very high frequency, and this induces electrical noise in nearby circuits. I don't have a 950 so I can't check, but the PDX10 does not seem to have this kind of dimming on it's LCD, the brightness control seems to affect some kind of processing of the video being sent to the display so it does not induce noise, at least not that I can detect with my PDX10.

The PDX10 does however have a two position menu setting for the viewfinder's backlight. I would recommend leaving this in the 'bright' position.
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