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Old Sep 13, 2012, 07:38 PM   #1
Notawiz
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Filtering loud sounds from audio stream

Hi all!

I would really like to find an application that filters or cuts out any sound above a certain volume limit.

There are several interesting public shows in YouTube that for one reason or another have a very poor audio quality. Sometimes the audio is clipping every five seconds. I need to boost up the volume a little to hear the speech, but then the clipping peaks begin to get extremely annoying.

Since the peaks are louder than the rest of the audio, and clipping is basically a straight line, it sounds plausible that one could make an application to analyze the audio stream and filter these peaks away - stop the loud noises before they even get to the audio circuits.

Do you know any application like this? I mean, it could be an app for the whole OSX, or just a plugin for Safari. Maybe even just for YouTube. So far I have only found applications that can limit the overall volume - but they just lower the volume, not removing the clipping sounds. Instead of listening to loud crackling, I'm left with quiet crackling - what's the point in that. The crackling still annoys me.

Thanks in advance for any ideas! :-)
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Old Sep 14, 2012, 11:15 AM   #2
paolo-
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One way to do it would be with AudioHijack. It allows you to insert plug-ins that are made for music production software like Logic and GarageBand (audiounits). A limiter would do 90% of what you want. It sets a volume limit and will reduce the volume of anything going over that limit.

I don't know of any other program than AudioHijack that will let you do this neatly. Soudflower (by cycling74) and AUlab(built in to the mac) might be able to do it for free but it would be kind of messy.
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Old Sep 14, 2012, 04:50 PM   #3
ChrisA
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Quote:
Originally Posted by Notawiz View Post
Hi all!

I would really like to find an application that filters or cuts out any sound above a certain volume limit.
...
What you are asking for is a "limiter". These are devices that will place a hard limit on the sound volume.

A less drastic device is a "compressor" these will bost the low volume sound and reduce the high volume sound.

Many times both devices are combined in one unit so that if compression is not enough the limiter can stop the volume. These are also "softer" limiters that take effect slowly. All of these devices are adjustable and some are frequency dependance say only (say) the bass is limited. Those might be called "multi-band compressor/limiters and have LOTS of knobs.

People have been using these the 60+ years in the studio but now you can get software versions and you allready have a software compressor/limiter on your Mac. it is part of Garage Band. Look for it.

Many outfits sell or give away software compressor or limiter plug-ins. Google will find them, or just use what comes with Garage Band

Last edited by ChrisA; Sep 14, 2012 at 05:02 PM.
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Old Sep 15, 2012, 02:11 PM   #4
localoid
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Quote:
Originally Posted by Notawiz View Post
... So far I have only found applications that can limit the overall volume - but they just lower the volume, not removing the clipping sounds. Instead of listening to loud crackling, I'm left with quiet crackling - what's the point in that. The crackling still annoys me.
Once you record an audio track that contains segments overdriven into clipping/distortion you'll never, ever going to be able to completely remove that distortion. "Quieter crackling" is all you're going to get from compression or limiting...
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Old Sep 15, 2012, 11:42 PM   #5
ChrisA
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Originally Posted by localoid View Post
Once you record an audio track that contains segments overdriven into clipping/distortion you'll never, ever going to be able to completely remove that distortion. "Quieter crackling" is all you're going to get from compression or limiting...
It was not clear to me that the audio was already clipped. I thought you had audio that was clipping and needed to hold the volume down to prevent that.

I think there are some things that have been done. It is far from perfct because clipping removes information and all you can do is guess what was removed. But the effect is, I think what you want

http://en.wikipedia.org/wiki/Clippin...clipped_signal

Search on "clip restoration". Lots of theoretical papers out there, not a lot of software.
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Old Sep 16, 2012, 06:34 PM   #6
localoid
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Quote:
Originally Posted by ChrisA View Post
It was not clear to me that the audio was already clipped. I thought you had audio that was clipping and needed to hold the volume down to prevent that.

I think there are some things that have been done. It is far from perfct because clipping removes information and all you can do is guess what was removed. But the effect is, I think what you want

http://en.wikipedia.org/wiki/Clippin...clipped_signal

Search on "clip restoration". Lots of theoretical papers out there, not a lot of software.
LOL, the Wikipedia article you cited talks about the theoretical restoration of a " soft-clipped signal" which more correctly should be called "soft saturation" (because clipping is hard saturation).

This article will probably give you a far better understanding about the differences between soft and hard saturation than what you'd get from the Wiki article.

If you can actually hear "crackle" in the original audio track (as the OP mentioned) there's not much hope that the track is suffering from "soft saturation", it's likely been badly clipped.
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