Reversing effects of over-attenuation/limiting at DVinfo.net

Go Back   DV Info Net > The Tools of DV and HD Production > All Things Audio

All Things Audio
Everything Audio, from acquisition to postproduction.


Reply
 
Thread Tools Search this Thread
Old September 18th, 2011, 06:54 AM   #1
Inner Circle
 
Join Date: Dec 2003
Location: Hampshire, UK
Posts: 2,205
Reversing effects of over-attenuation/limiting

I have some interview audio which has been recorded way too hot, either at the camera or at the wireless end, not sure which (not my audio). The waveform is basically flat throughout and it sounds ghastly.

I'm not expecting miracles, but is there anything that can be done to partially rescue such audio? Would an expander help?

All advice welcomed.
Ian Stark is offline   Reply With Quote
Old September 18th, 2011, 08:10 AM   #2
Inner Circle
 
Join Date: Mar 2005
Location: Hamilton, Ontario, Canada
Posts: 5,742
Re: Reversing effects of over-attenuation/limiting

Expander not likely to help. The problem isn't that the difference between the lowest and the highest level signals is too little, it's that the tops of the waveforms have been sliced off, turning them into dirty square waves that generate oodles of hashy-sounding high order harmonics when played back. You need to lower the overall level and restore the waveform tops. There is software available to do that but how successful it is depends on how severe the problem is to begin with - there's only so far that software can go towards accurately guessing what information was lost in the clipped off portions. Take a look at SoundForge and Audition, they both have clip restoration tools. Another good one is Izotope's Rx. Search Google for Declipper and Clip Restoration.
__________________
Good news, Cousins! This week's chocolate ration is 15 grams!
Steve House is offline   Reply With Quote
Old September 18th, 2011, 02:12 PM   #3
Inner Circle
 
Join Date: Dec 2003
Location: Hampshire, UK
Posts: 2,205
Re: Reversing effects of over-attenuation/limiting

Steve, thanks for such a helpful response. I have an older version of Sound Forge (I mean REALLY old). I'll see if I can upgrade. I did look at Rx some time ago, specifically to remove aircon hum etc. I ended up using Waves X-Noise which has proved to be excellent (but not for this job, obviously). Time to look at Rx again I think. Seems to be very highly regarded. Thanks again.
Ian Stark is offline   Reply With Quote
Old September 18th, 2011, 04:34 PM   #4
Trustee
 
Join Date: Jan 2011
Location: Pennsylvania
Posts: 1,359
Re: Reversing effects of over-attenuation/limiting

Ian,

When you say "the waveform is basically flat," is that just when you're zoomed out and looking at several seconds of the file?

The important question is: how does the waveform look when you zoom in enough to see individual cycles of the sound? (I'm thinking that the entire horizontal axis of the display would be around 10 msec to see this much detail.)

If you look at the individual cycles of the audio, and the tops and bottoms are clipped perfectly flat at 0dBFS, then you've got digital clipping in the recorder. Audition can repair that, but only to a limited extent.

If the individual cycles are somewhat flattened, but at a level lower than 0dBFS, then the clipping probably occured earlier in the chain, and the audio might have other problems more complex than the flattened waveform. In that case, all bets are off.

You might want to submit a 30-second sample of your file so we can look and listen.
Greg Miller is offline   Reply With Quote
Old September 18th, 2011, 04:42 PM   #5
Inner Circle
 
Join Date: Dec 2003
Location: Hampshire, UK
Posts: 2,205
Re: Reversing effects of over-attenuation/limiting

Thanks Greg,

I'm not in front of it right now but as soon as I get a chance I'll check that out and respond. Thanks for the comment.

I completely realise that miracles aren't going to happen here, and I'm fairly sure that the clipping occurred at the radio mic, based on what the girl who shot the piece told me, so I fear the worst.

Anyway, I'll come back with more info as soon as I can.

Cheers.
Ian Stark is offline   Reply With Quote
Old September 19th, 2011, 10:01 AM   #6
Trustee
 
Join Date: Aug 2008
Location: New York
Posts: 1,840
Re: Reversing effects of over-attenuation/limiting

As Greg stated, if it's a question of moderate digital 'overs', clipped peak restoration software can often help, depending on the severity. If the problem is an over driven pre-amp, that's usually not salvageable, at least to the point of making it sound decent.
Rick Reineke is offline   Reply
Reply

DV Info Net refers all where-to-buy and where-to-rent questions exclusively to these trusted full line dealers and rental houses...

Professional Video
(800) 833-4801
Portland, OR

B&H Photo Video
(866) 521-7381
New York, NY

Z.G.C.
(973) 335-4460
Mountain Lakes, NJ

Abel Cine Tech
(888) 700-4416
N.Y. NY & L.A. CA

Precision Camera
(800) 677-1023
Austin, TX

DV Info Net also encourages you to support local businesses and buy from an authorized dealer in your neighborhood.
  You are here: DV Info Net > The Tools of DV and HD Production > All Things Audio

Thread Tools Search this Thread
Search this Thread:

Advanced Search

 



Google
 

All times are GMT -6. The time now is 10:36 PM.


DV Info Net -- Real Names, Real People, Real Info!
1998-2017 The Digital Video Information Network