Correcting 'clipped' audio

jonathan-kenefec wrote on 7/17/2008, 4:56 PM
A kind soul from this forum recently helped identify a problem with a scene I shot (namely clipped audio due to my audio input being too high).

Are there any free programs that can correct this? I tried audacity but it doesn't seem able. The one I was pointed to was way too expensive (over 1K)!!

Or if anybody can correct the file for me I'm happy to pay a fee...(within reason) :-)

Cheers

Jon.

Comments

rs170a wrote on 7/17/2008, 5:14 PM
iZotope RX, the one everyone here is raving about, is only $350.00 U.S.
RX Advanced is $1,200.00 but you don't need that.

Mike
johnmeyer wrote on 7/17/2008, 5:30 PM
iZotope RX has much better clipping restoration than the Sony Noise Reduction, but the Sony product does work. I have Sound Forge but haven't upgraded in a long time. I think this may now be included in SF, but someone else will have to correct me.
Steven Myers wrote on 7/18/2008, 3:17 AM
Sound Forge does now include Clipped Peak Restoration, and it does work. Sometimes.
Its definition of clipping is pretty much restricted to truly flat tops at 0dB.
farss wrote on 7/18/2008, 3:50 AM
"Its definition of clipping is pretty much restricted to truly flat tops at 0dB. "

True indeed however this is easily fixed. Apply just enough gain to get hard digital clipping and then use the Clipped Peak Restoration FX. I've also used this technique to get useful repairing of analogue overloading.

However do not expect miracles. If you've seriously clipped the audio that's it, it's fried, toasted and burnt on both sides. Also the degree of repair possible depends on the nature of audio. Complex sounds will loose a lot of the original data when clipped.

Bob.
Steven Myers wrote on 7/18/2008, 5:23 AM
True indeed however this is easily fixed.

That's true, too, if we can all agree to be loose with the definition of "easily." Heh.
I have successfully used that technique at times, but sometimes it requires a painstaking surgical approach.

Another Sony limitation is that it makes all the clipped peaks perfectly round.
OTOH, RX guesses at what the peaks would look like in real life. Whether or not the results are really as they would have been without the clipping, I have no idea. But they look real. Heh again.
baysidebas wrote on 7/18/2008, 7:32 AM
Of course, the answer is to not clip on recording.

One technique I use when the audio feed is mono, and I have two channels available, is to set the gain on the second channel to 9 or 12 db below the first.and feed the incoming to both That gives me the additional headroom just in case it's needed.
johnmeyer wrote on 7/18/2008, 8:07 AM
Of course, the answer is to not clip on recording.

I just restored a tape recorded in 1950, which had amazing amounts of hum and clipping. I tried to find the recording engineer so I could fire him ...
baysidebas wrote on 7/18/2008, 8:35 AM
That wasn't me! I swear... although, does anyone here remember paper backed magnetic recording tape? unless you set the level for clipping on those, the signal would get buried in the background noise. Those were the days, louder was always better, even the marketing hype was there: "Our amplifier's volume controls go to 11, where all others go only up to 10."
farss wrote on 7/18/2008, 4:12 PM
That must have been some recording engineer. According to my history books digital recordings didn't exist until decades later so clipping wasn't possible in 1950.
What I do find amusing is the amount of money some will spend to recreate the sound from back then of magnetic devices pushed beyond the limits of the B/H curve.

Bob.
johnmeyer wrote on 7/18/2008, 5:09 PM
According to my history books digital recordings didn't exist until decades later so clipping wasn't possible in 1950.Believe me, it is very easy to saturate almost any analog amplifier design, whether tube base, bipolar transistor, MOSFET, class A, B, C, etc. You can feed it "11," but if it's only got "10" in the tank, that's all you're going to get, and the result is a clipped peak. What's worse, you usually also get distortion as the amp nears saturation and, unlike peak clipping, you end up with intermodulation distortion which is ugly to listen to and impossible to remove.

farss wrote on 7/18/2008, 5:51 PM
Yes, that was kind of my point, over saturation (aka distortion) is a different beast to clipped. With digital clipping the waveform is perfect until it clips, with analogue over saturation you get a roll off and/or as I've seen happen you then get sag. Impossible to fix to any extent as because as you've noted the intermodulation distortion cannot be removed. The latter also happens with bad digital clipping.

Bob.