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Sony PMW-300, PXW-X200, PXW-X180 (back to EX3 & EX1) recording to SxS flash memory.


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Old October 6th, 2015, 06:38 AM   #1
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Internal mic interference tone on PMW300

With the inclusion of internal mics built in to the camera, this has saved me from taking along extra mics and cables for atmosphere/crowd audio when shooting events. However, lately, I have been noticing an unwanted interference that has been in the audio tracks 3 and 4 that these internal mics record to.

The attached audio sample visual clearly shows the noise that is present at the 2k frequency.

The .wav audio file attached has a sample of this with the noise, and the 'after' where it (and some background rumble) has been cleaned out with izotope RX4. Yes, it's an easy fix but I shouldn't have to do it on audio from a $10k camera.

I was originally thinking that this could have been noise presented on the electrical circut that the camera was plugged in to when powered by the adapter brick, but this latest recording from last night was done running off battery only.

I'm inclined to think that it might be the noise from the fan from inside the camera. Any thoughts?

Andrew
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Internal mic interference tone on PMW300-internal-mic-interference.jpg  
Attached Files
File Type: wav PMW300-internal-mic-noise-before-and-after.wav (1.63 MB, 34 views)
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Old October 6th, 2015, 08:55 AM   #2
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Re: Internal mic interference tone on PMW300

Not exactly relevant to your modern camera, but my old V1E (bless its memory!) had exactly the same problem, except that the frequency was ca 1.5 kHz. I never did track down the cause, but I did think of the fan at the time, but then of course there was also the tape mechanism.

I ended up saving an Audition noise profile to remove it when necessary, but, as you say, you should not have to do that.

Fortunately my current EX3 seems to be immune.
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Old October 6th, 2015, 09:17 AM   #3
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Re: Internal mic interference tone on PMW300

Not noticed this with my PMW-300. Mind you, I rarely use the audio from tracks 3 & 4 anyway - but it's great that they are there if needed - and they have saved my bacon more than once!

Just an idea... Maybe if you attach a shotgun mic (or whatever mic you have) to an XLR cable and feed the sound into the PMW-300 via channels 1 or 2. Put this mic really close to where the fan vents are and capture some audio. If it is indeed the fan noise that the internal stereo mics are picking up, then I would expect the noise print/analysis of the resulting audio track to show a similar 2 kHz tone as per your screen shot/audio file.

Did the V1 have a fan? So long since I used one I've forgotten. I'm sure my EX3 did not have a fan - but may have remembered that wrong!
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Old October 7th, 2015, 08:38 AM   #4
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Re: Internal mic interference tone on PMW300

That's a great idea, Andy. I'll have to try that.

If you can take a look at the internal mic tracks 3 & 4 from recordings on your PMW300 then it would be greatly appreciated. I don't know anyone else over here with this same model. (It might take a long recording for the camera to decide that the fans need to kick in.)

Andrew
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Old October 11th, 2015, 12:24 PM   #5
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Re: Internal mic interference tone on PMW300

This may well be a silly question but nothing ventured, nothing gained.

Did you have phantom power operating on any vacant external mike channels? It sounds a little like the phantom power break-through you hear sometimes with a dirty XLR pin or dud cable.

It also seemed like your mike was some distance from the subject and a lot of gain was needed to bring the voice up which in turn will bring up any noise floor, whatever form it may take.

Your noise reduction technique seems to have worked fine.
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Old October 12th, 2015, 05:58 AM   #6
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Re: Internal mic interference tone on PMW300

I don't mind silly questions at all. :-)

I have one of the mic inputs always left with phantom on as I mostly always have a NTG2 plugged on to it. In this recording it wasn't being used, but I have one from Saturday where it's plugged in and the same interference is still present in lines 3 and 4 from the internal mics..

Also, I have recordings where you can see the noise (in a spectral view in Izotope RX4 etc) start from a slightly lower frequency to where it sits ... much like the view of the electrical interference from an electrical motor if you've ever had that happen. (a rising curve in the frequency before it continues along on a flat line) This is why I am suspecting that it could be the internal fan when it kicks in and comes up to speed.

The camera was about 10 metres away (or less) and I was using a lapel mic to get speaker audio (into channel 1). The internal mics were for 'crowd mic' use only, and are probably on auto-grain by default..

Andrew
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Old October 12th, 2015, 07:39 AM   #7
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Re: Internal mic interference tone on PMW300

Yes, the internal stereo mics on the PMW-300 are ONLY auto gain. This means they will pump up the noise floor if they think it's a quiet environment. (I'm sure you know this - just clarifying for anyone who might not know or have a PMW-300)
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Old November 13th, 2015, 09:47 AM   #8
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Re: Internal mic interference tone on PMW300

Just some updates.

I've shot an event in a room that we shall say was "very well air-conditioned" and the fans and their noise via the internal mics did not kick in.

Also, I have since put my ear up to the rear of the camera (where the fans are) and I can hear the tone that is being spilt over to the internal mic recording.

Finally, I've been speaking with the Sony support people in Australia and they could barely remember the last time a PMW-300 came in for a service/repair, and even then it was a QA check prior to a sale. In other words, the camera is otherwise exceptionally reliable thus far.

Andrew
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Old February 24th, 2016, 08:06 AM   #9
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Re: Internal mic interference tone on PMW300

Was there any solution to this?

I get exactly the same problem on both internal channels but it starts around 45minutes or so into the recording suggesting it is fans. External mics work fine.

Thanks - John
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Old February 28th, 2016, 01:37 PM   #10
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Re: Internal mic interference tone on PMW300

Hi John,

Firstly an update with the response from the Aust-NZ Sony tech support people (who, by the way, tell me that the camera model doesn't generate any service call thus far ... very reliable model).

Quote:
There are two possible solutions to this issue.

The first is the fan control setting under OTHERS in the menu.

The default is “Auto”, but the other option is “Off in Rec” (Record).

I would advise setting to “Off in Rec” when the internal mics are used.

(image of related text from manual)

Of course all fans make some noise, it is inevitable, and the internal mics are very sensitive. Also if mic control is set to Auto then the mic AGC will increase when the ambient sound level is low thus exacerbating the background fan noise.

The alternative is to use an external directional mic via the external XLR input(s).

This has two advantages, a) the mic is somewhat mechanically isolated from the camera, and b) the mic being directional will minimise pickup from within the camera.
I'm still in two minds about the camera shipping with this issue still present. After all, what is the point of having the internal mics in the camera if you don't get a professionally acceptable recording quality in the 'native' mode of how the camera is set to operate? Also, from what I have seen the level of ambient noise makes no difference to the level of the unwanted fan noise.

The attraction to me for these internal mics is that it saves me from lugging in a audience mic (plus lead and a comparatively PITA mic stand) every time I record an event. The quality of the in-built mics is brilliant, and it gives me an appropriately stereo recording source for the ambience / audience.

I've since changed the "fan control" setting to "Off in rec." which as you can guess keeps it off when the camera is in recording mode. Under this setting, the fan will only automatically come on whilst recording if an excessive temperature is reached ... in which case you want it to come on.

The only thing you lose in having the fan in this mode is a theoretical shortening of the life span of electronic components from the camera internals being allowed to get to a higher temperature during operation. On a practical level, I'm not sure that we would ever notice this downside.

Andrew
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Old February 28th, 2016, 02:35 PM   #11
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Re: Internal mic interference tone on PMW300

Here is a video recording that I've recently made with the internal mics used and the internal fan set to be off during recording.


The main speaker in this video has a RodeLink wireless lapel mic attached, feeding to the first channel in the camera. Second channel is a Rode NTG2 boom mic and the remaining third and fourth channels are from the internal mics which are set to auto-gain. Come to think of it, I don't know that you can set the internal mics to anything else. :-)

It was only when I arrived that I realised that there would be a person making the introduction, and I just happened to have a Zoom H1 unit in my audio bag and this was placed in his suit pocket, operating in 24-bit 48k wav recording mode with auto-gain on.

The video was recorded in the function room of a regional area motel, and the room set-up per the venue seating layout was such that the speaker was in the comparatively un-lit (read 'dark') area of the room. No video lights were used, and the camera was on its highest sensor gain setting (per my internal setup profile) of 12db and I had about one stop left on the iris ring. I'm quite impressed with what the camera produced for an image in spite of all this. Running on auto white balance, some colour correction tweaking has been applied to the video to give what you see here.

On a side note, you will notice that the introductory speaker is out of focus. I'd already pre-set the full manual focus of the camera to be correct for where the speaker stands at the lectern. Being a one camera setup, the last thing I wanted to be doing was to be finding the focus again when the main speaker first comes to the lectern. For this reason, I deliberately did not correct the focus when the person doing the introduction moved around and exited the 'diameter distance' of correct focus. It's just not worth it, especially under the lighting conditions and the shallow depth of focus that you have to work with when the iris is opened so wide.

The first thing that one does with the audio (editing in Premiere Pro CS6) is to send the timeline sequence audio over to Adobe Audition, and I then take the extracted audio wav files in to Izotope RX and use their awesome denoiser plugin to sample and remove the room tone ... which once again is the rumble of the air-conditioning. This was applied to audio recordings from the lapel mic and internal mic. Various other audio work was done in Audition, including applying a multi-band compressor to the audio from the main speaker and crowd mics (internal camera mics). The audio in channel 2 from the Rode boom mic was not used, but is a handy backup in case of a mic failure.

There was no internal fan noise that needed to be removed from what was recorded via the internal mics in the camera.

If you watch a sample of the video recording from 32:48 onwards, you will hear a good sampling of not only the clarity of the applause but also the laughter and cheering from the audience of about 90 in the room. I'm quite happy with the result.

Andrew
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Old April 26th, 2016, 07:29 AM   #12
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Re: Internal mic interference tone on PMW300

Andrew

Apologies for late response but I forgot to subscribe to the thread. Thanks for the update etc. I have turned off the fans as suggested. I was not sure whether to do that or not but as the camera is used infrequently then I am sure the MTBF of components will not be overly reduced.

Will have a good test when my camera is being used to record the local mayor making ceremony end next month as will need to use all 4 channels of sound. I'm sure will be OK.

Thanks again - John
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