Tips and Tricks 3 ‘Digital Clipping’

Tips & Tricks

Working in post production can be great, however, you usually end up spending most your time fixing other people’s mistakes, the other day I came across what I now jokingly call square wave files. Below is what happens when a video editor tries to do an ADR Session.

Squared off audio file, very obvious clipping.

Same audio as above, without clipping. how it should look. (Declipped by izotope)

Distortion can occur for various reasons, however arguably the worst kind is digital clipping, it sounds awful and can be impossible to repair.

Digital Clipping occurs when the sound exceeds 0dBFS this means there is no more room to include extra data within the format so it just gets chopped off, usually you can just turn down the volume (before the conversion) reducing the scaling of the data meaning it will fit within the file.

How do you detect clipping?

Well other than just listening to the audio whilst you are recording almost every piece of audio equipment will have a clipping light or indication on its display,  it is usually red.

The red (O/L) overload light shows it is clipping

The red peak light on the side shows the audio is clipping

 

 

 

 

 

 

 

 

In preventing digital clipping there are two options: the first is to turn down the gain knob (or rocker, etc.) until the audio isn’t clipping until the light never flashes.

Make sure you test clipping with the loudest source you going to record. So if that is a person and they will be screaming in the scene you need to have them scream as loud as possible to test the gain.

Unfortunately, sometimes this will still not be enough, imagine recording a gun close up, so there is another alternative, an analogue compressor or limiter. This should be put before the digital converter to work (DIGITAL LIMITERS ON RECORDERS DO NOT WORK) this can be a physical external unit or built into normally more premium devices.

A compressor/limiter should (once set up) automatically pull the volume down after it exceeds a certain volume threshold. Meaning once set correctly it will never clip, this still changes the way it sounds but sounds much nicer than clipping.

Using the above information should help anyone to get a better recording. To be fair to my friend who did this recording I don’t expect video editors to know this so there’s no embarrassment to it. But really this is why us audio guys get paid because we know the problems and more importantly how to solve them before they become a problem in the first place.

 

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