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Decibels, what do they do? Part3 dBFs and clipping.
Once an audio signal has been acquired in the digital domain there is no need for voltage reference value as the signal is represented in “1” & “0”.
Whatever input or output your card is calibrated for, 0dBFs is the maximum internal digital level that it can accommodate before getting into severe distortion. The picture above illustrates this: the red lines indicate 0dBFs and the signal (in black) is pushed too far and clipped.
Red lights are there to warn you. When you are mixing or recording you need to watch out for them as they indicate one form of distortion or another. Some DAW have got a built in tolerance to distortion, however unlike analogue gear where distortion might be desired and a good thing to have, digital distortion can only lead to nastiness and artifacts: AVOID AT ALL COSTS!
if we wanted to show a sine wave clipping, we could do this easily by connecting an oscilloscope to the output of a device, a microphone preamp, a compressor or similar.
As you can see from the picture on the left both the top and bottom parts of the sine wave are clipped. This is called symmetrical distortion. This might be a wanted effect, but it does change the nature of the sound and adds what is called Total Harmonic distortion or THD. We will discuss this subject in another post dedicated to it. For now let’s concentrate on digital distortion inside your DAW.
Although this could have a beneficial effect on some analogue gear it is not recommended that you try and do that inside of your DAW as the results are likely to lead to loss of depth, artifacts and other unpleasant ripercussions.
There are several ways of ensuring you are not clipping your files, these range from plug ins inside your DAW to stand alone software with both paid or free options available. What we tend to use are applications or plug-ins that allow real time checking and to adjust the processing accordingly to avoid any clipping. It is, however entirely up to the engineer and her workflow to choose how to do it. Here are some options of both plug-ins and stand alone software, with both paid for and free options:
–iZOTOPE Rx Very powerful suite of plug-ins, this is our de-facto choice not only because of its versatility but also for the sheer amount of different remedial tools that will help you repair any problems.
–AudioLeak Also available for free! This is a Mac only stand alone software that performs a wide variety of level tests, from FFT to peak level to batch files analysis and processing. Powerful stuff.
Some free options are:
–Youlean This is a great free option with support of several standards. the paid subscription includes a ton of other very useful features, presets and drag and drop functionality. Check it out!
–Voxego SPAN FFT,Stereo ,M-S & Surround meter, Stereo correlation meter, EBU and K-system (thank you Bob Katz for this!) as well as RMS, true peak level and clipping detector. Did we mention is free?
–SSL X-ISM (inter sampling meter), not supported by Solid State Logic anymore (hence the link is not official) but a great (free!!) tool to have in your arsenal (while it works).
If you like to write your own code and use an Apple computer, there is another way for you to check if an audio file has clipped. This is a post processing application, so can only be performed after the mix or after the file has been processed.
1.Open Terminal
2.Type “afclip” with a space after
3.Drag a file (or a bunch of them) onto the window
4.Hit Enter
5.After a little while you’ll see one of the following three messages:
This is part of the of the Mastered for iTunes procedure: FUN STUFF!
In our next Blog article we’ll talk about RMS levels, Parallel Compression and how they go hand in hand. Stay tuned!
