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Mysterious hum

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Steve Adams
Mysterious hum
on Feb 9, 2019 at 4:25:53 am

I shot a 1080P video with an iPhone 6 using a lapel mic as I followed a store manager around her store and she talked about various items. When I played the video back on the iPhone the audio sounded great, with no hint of a hum. But when I uploaded the .mov file from the iPhone to my desktop and then loaded it into PP CC2017 the audio had a strong hum. I was able to get rid of it with the PP audio notch filter centered at 60Hz but I can't understand where this hum came from. The iPhone, of course, has no 60Hz in it, and I didn't hear any hum when I shot the video. So what is the source? Has anyone else experienced this or have any idea what it could be?

Thanks


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Bouke Vahl
Re: Mysterious hum
on Feb 9, 2019 at 8:11:21 am

60 Hz is the AC power frequency in some countries.
That means the source could be lights (they have them in supermarktets, lots of them), fridges, airconditioning, basicly every thing that uses power could be a source of interference.
For this balanced audio is designed, so at least the cables won't pick up the noise.
However, a humming deice with no electronic interference makes sound, so if you mic picks up that you have the wrong mic for the job.

Now, of course your phone does not let you hear this, 60 Hz is very low, the speaker is probably not able to playback a frequency that low.

So, now you know why there are dedicated sound guys who bring 10K worth of equipment to do a job like this.
I'm not saying that that is needed for such a job, but shooting something with too cheap equipment / not enough known how is not the way to go. Having to do a lot of work in post that never give you as good results as that you would have gotten in the first place makes it more expensive than doing it right the first time.

Bouke
http://www.videotoolshed.com


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Steve Adams
Re: Mysterious hum
on Feb 9, 2019 at 10:37:30 am

Yes, what you say makes sense. I'm sure the iPhone speaker can't produce 60Hz, so, of course, the video sounded great played back on the iPhone. It's puzzling, though, that I didn't notice any hum when I was following her around the store but in the video playback the hum dominates the audio. And at one point the hum disappears for about 5 seconds and then comes back on! There must be some machine in the area that gets turned on and off.

Thanks for the input.


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Joseph W. Bourke
Re: Mysterious hum
on Feb 9, 2019 at 5:42:23 pm

Probably a compressor on one of the refrigeration units is going on and off.

Joe Bourke
Owner/Creative Director
Bourke Media
http://www.bourkemedia.com


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Dave LaRonde
Re: Mysterious hum
on Feb 9, 2019 at 7:30:39 pm

Everyone knows those "shot on an iPhone" spots... and indeed they were.

What the spots DON'T say is that those iPhones were tricked out with every possible gizmo and app to ensure best results and that they were shot by pros with audio recorded by pros.

If you think any ol' iPhone will yield the results in those spots, think again.

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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Steve Adams
Re: Mysterious hum
on Feb 12, 2019 at 7:07:12 am

Actually, the iPhone had nothing to do with this hum, and the 1080P video it generated was gorgeous.


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