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11-13-2014, 07:25 PM   #1
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SR characteristic sound frequency(ies)

Last October, I recorded the sound of a tidal bore at night. Preliminary comments and a photograph of the daytime bore were posted at:
https://www.pentaxforums.com/forums/22-pentax-camera-field-accessories/275789...o-shotgun.html

At night (about 01:00), the sound of the tidal bore was recorded by the Rode Stereo Videomic Pro (stereo) mounted on my Pentax K-3 SLR camera's hotshoe. The sound record was sub-sampled into sub-sets 2 s long, frequency analyses were conducted and the data were averaged for several successive periods. (In addition, the PSDs of left and right tracks were averaged.) The results are included in the attached plot. On the plot, the peak in energy above 50 Hz is definitely caused by the rumble noise of the tidal bore. On the other hand, you will note that all the data showed some sound energy between 5 and 30 Hz, irrespective of the time and of the proximity (or not) of the tidal bore.

I suspect that the sound energy between 5-30 Hz might be possibly caused by the 'shake reduction' of the Pentax K-3 camera, that I forgot to disconnect.

Does anyone have information on the characteristic sound frequencies of the K-3 SR system?

I would be grateful by any comment, reaction and suggestion that anyone might have. Thank you in advance for any constructive input and comment.

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11-13-2014, 10:47 PM   #2
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It's a bit hard to see in the plot, but given the apparently narrow bandwidth you may be right.
although personally I would expect the SR system to be in the KHz range, i could be wrong.

I'd also be looking at what is the mics frequency response is like at those frequencies,
being below normal human hearing means it may do all sorts of [undocumented?] things.

I'd be interested to see what it ends up as. good luck
11-13-2014, 11:03 PM   #3
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Should be fairly easy to isolate the SR sound by taking records with SR on and off.
11-14-2014, 02:18 AM   #4
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Planet earths native Resonance as of late was 7.8 Hz human hearing is 20Hz-20Khz so tidal bore and subsonic rumble make sense

11-19-2014, 05:00 AM   #5
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QuoteOriginally posted by Not a Number Quote
Should be fairly easy to isolate the SR sound by taking records with SR on and off.
It's not that easy as the SR system is always active when the mirror is up, on or off just selects different running modes.
11-20-2014, 03:24 PM   #6
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Thank you everyone for the suggestions. I did some complementary test, with the same camera (my K-3) and microphone (Rode VideomicPro):
(a) the Rode shotgun mounted on the camera hotshoe and
(b) the Rod Shotgun placed 20 cm away from the K-3.
The tests were conducted at night with minimum background noise. All the camera settings were otherwise identical for all tests. (The lens was a MF lens.) For each test, the sound record was sub-sampled into sub-sets 2 s long, frequency analyses were conducted and the data were averaged for several successive periods. (In addition, the PSDs of left and right tracks were averaged.) The results are included in the attached plot together with the earlier tidal bore data.

The blue curve show Test (a) with the Rode shotgun mounted on the camera hotshoe. The red curve presents Test (b) with the Rod Shotgun placed 20 cm away from the K-3. We can see a marked difference in energy at low frequency (10-30 Hz), suggesting that the microphone mounted on the hotshoe pickup some low-frequency noise, very likely out of the camera. I cannot definitely confirm that the SR is the main cause of that noise, but it might be one effect.


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11-20-2014, 05:05 PM   #7
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I may be entirely wrong here, but from my understanding the shake reduction in video mode does not actually shift the sensor around (in contrast to the K5) - it's purely software.
11-20-2014, 06:23 PM   #8
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QuoteOriginally posted by rthur Quote
I may be entirely wrong here, but from my understanding the shake reduction in video mode does not actually shift the sensor around (in contrast to the K5) - it's purely software.
You might be right. Then there must be something (or some things) inducing low frequency (<40 Hz) vibrations to the camera body. Any comment/suggestion must welcome.

11-21-2014, 05:01 AM   #9
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Again, the SR system is still active even if it's switched off (as long as the mirror is up). The image-sensor is held in place during exposure by the same servos that move the sensor around during active shake reduction. They need power to hold the sensor still, and they emit sounds while doing so.

During mirror down (and power off) the sensor is free to move around inside the camera, which often results in the famous "what is loose inside my camera"-question.
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