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looking for a sound distorter so the conversations of bystanders picked up by the mic cannot be understood

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TImo Limo
looking for a sound distorter so the conversations of bystanders picked up by the mic cannot be understood
on Nov 5, 2011 at 12:22:09 pm

My rather mundane goal is to have a video of a soccer game with all the crowd noise and cheering but with the conversations of people who were standing near my video get distorted in some way so their conversations "overheard" by the microphone cannot be understood, and so that someone cannot easily "reverse engineer" the distortion and recover what they were saying. I don't want to replace the soundtrack with music--hoping to preserve the authentic crowd noises and cheering.

I would like to extract the audio track from an MP4, run it through some kind of filtration software that will obfuscate what people are saying, and then reattach the obfuscated/garbled soundtrack to the video without any timing alignment issues. It would be ok if the crowd's cheering got distorted too, as long as it was still recognizable as cheering.

Donation-ware preferred.

Thanks for suggestions.


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Steve Kownacki
Re: looking for a sound distorter so the conversations of bystanders picked up by the mic cannot be understood
on Nov 5, 2011 at 2:01:44 pm

Why not put a wireless mic on a stand some distance from the crowd down near the field pointing back at them? You'd hear the cheering and announcer clearly but no distinct conversations. Plus you eliminate post-production.

Steve






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TImo Limo
Re: looking for a sound distorter so the conversations of bystanders picked up by the mic cannot be understood
on Nov 5, 2011 at 3:04:18 pm

Sorry, my question was unclear. Your response makes perfectly good sense, but the MP4 already exists. I'm trying to fix the existing problem rather than avoid it in the future :-)


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Craig Alan
Re: looking for a sound distorter so the conversations of bystanders picked up by the mic cannot be understood
on Nov 6, 2011 at 2:37:56 am

Unless the unwanted conversation is constant, you could edit around it by filling in the unwanted conversation with crowd noise that matches from other sections. This will be tedious but doable. To find good matches for the unwanted sections look for similar waveforms coming from the crowd. You can play with levels until the sequence sounds like a natural flow. Crowd noise tends to be a steady buzz and sudden swells. Put the filler on a different track and line up the waveforms to match. Cut out the unwanted dialog and have a listen. You will not even have to cut it all out to make it fairly meaningless.

It must have been a hell of a conversation for someone to want to "reverse engineer" the distortion and recover what they were saying.

Never a good idea to have the mike attached to the camera. Not only do you pick up unwanted conversations but you need to be silent through the entire shoot.

OSX 10.5.8; MacBookPro4,1 Intel Core 2 Duo 2.5 GHz MacPro4,1 2.66GHz 8 core 12gigs of ram. GPU: Nvidia Geoforce GT120 with Vram 512. OS X 10.6.x; Camcorders: Sony Z7U, Canon HV30/40, Sony vx2000/PD170; FCP 6 certified; write professionally for a variety of media; teach video production in L.A.


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Bill Davis
Re: looking for a sound distorter so the conversations of bystanders picked up by the mic cannot be understood
on Nov 6, 2011 at 2:46:45 am

Timo,

Unfortunately what you're asking just isn't practical.

On a video signal, you can separate out and "blur" some pixels leaving others clear because you're working with a grid of individual addressable pixels.

Sound is NOT like that.

It's a stew of frequencies all of which reach the microphone at (more or less) the same time. What makes some sounds stand out over others is their amplitude verses the other parts of the sound stew. That amplitude is a property of physics that is based on proximity of the sound causing source to the microphone. So someone closer to the mic will "stand out" in the mix from the other sounds - and there's simply nothing you can do to alter that fact (other than to tell the person closer to the mic to shut up.)

There's simply no way to artificially PUSH BACK a particular sound into the mix unless theres something significantly DIFFERENT from it and all the other voices being recorded. And human voices are in such a narrow range of tones and complexity that one is just too similar to another.

Sorry.

"Before speaking out ask yourself whether your words are true, whether they are respectful and whether they are needed in our civil discussions."-Justice O'Connor


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TImo Limo
Re: looking for a sound distorter so the conversations of bystanders picked up by the mic cannot be understood
on Nov 6, 2011 at 3:46:52 pm

Thanks for the explanations. I will just have to do the tedious editing.

The mic picks up some interesting things when people think there's so much ambient noise their conversations cannot be overheard. So I wanted to make sure any "sound-obfuscating" filter (if there were such a thing) could not simply be removed, leaving the original sounds perfectly audible.


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Craig Alan
Re: looking for a sound distorter so the conversations of bystanders picked up by the mic cannot be understood
on Nov 6, 2011 at 7:25:21 pm

I doubt that this could be done. They broadcast interviews with the sound of the speaker disguised through distortion and the face masked to protect the identity of the subject. You could only undo it if you opened the original project file and removed the filter. But with the advancement of software who knows. Again even if this were possible they would need to be highly motivated and skilled.

You could also cut out sections of the audio recording by going to a voice over track of an announcer.

OSX 10.5.8; MacBookPro4,1 Intel Core 2 Duo 2.5 GHz MacPro4,1 2.66GHz 8 core 12gigs of ram. GPU: Nvidia Geoforce GT120 with Vram 512. OS X 10.6.x; Camcorders: Sony Z7U, Canon HV30/40, Sony vx2000/PD170; FCP 6 certified; write professionally for a variety of media; teach video production in L.A.


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Eric Toline
Re: looking for a sound distorter so the conversations of bystanders picked up by the mic cannot be understood
on Nov 6, 2011 at 8:04:56 pm

Just wondering why it's important to "blur" the off camera voices?

Eric


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TImo Limo
Re: looking for a sound distorter so the conversations of bystanders picked up by the mic cannot be understood
on Nov 6, 2011 at 9:03:20 pm

Blur the conversations because of what's being said by people about other people or about themselves, things they wouldn't want to have on a soundtrack. This was a high-school sporting event. You know, sex, drugs, rock-and-roll.


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Ty Ford
Re: looking for a sound distorter so the conversations of bystanders picked up by the mic cannot be understood
on Nov 16, 2011 at 4:50:57 am

Hello Timo,

You got the best advice you could get from the group. BTW, in the future, Try alcohol in the people speaking. It usually blurs things pretty well.

Regards,

Ty Ford

Cow Audio Forum Leader
Want better production audio?: Ty Ford's Audio Bootcamp Field Guide


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Ty Ford
Re: looking for a sound distorter so the conversations of bystanders picked up by the mic cannot be understood
on Nov 16, 2011 at 12:47:25 pm

Timo,

As I slipped off to sleep last night, it occurred to me that there may be a solution.

Several of the audio noise reduction softwares have graphical interfaces. iZotope's AudioRX and the NR features of SoundTrack Pro both offer this. I don't have a lot of time on these systems and don't know how long it would take for you to process a long section, but the idea is this.

You see horizontal and vertical display showing frequency over time. sound appears as smudges or different colored densities. You can use a pencil or lasso tool to select the offending sounds and delete them. You need to have some finesse, but I have heard pretty amazing results; like removal of a whistle, clank or extended scream.

How that figures into your situation, I don't know. Sounds like you're trying to process a whole lot of sound as one might by altering the depth of field with a lens. As far as I know, there isn't a software to do that.

Regards,

Ty Ford

Cow Audio Forum Leader
Want better production audio?: Ty Ford's Audio Bootcamp Field Guide


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