Audacity Effects: Amplify (3) – Some Clipping Details


In the previous article we talked about “allow clipping” for “amplify” effect. By checking the “allow clipping” option, you allow the signal to be amplified above the maximum level, so distortion or clipping will occur. In this article, we will examine how data is affected or not affected internally.

The figure below is a generated signal at 220 Hz with an amplitude of 0.8 (or -1.94 db).


I took a portion of the signal and amplified it by 10 db (with “allow clipping” checked), and below is the signal after amplification. You can clearly see the distortion/clipping. You can also hear the distortion if you play it.


But if I now reduced the amplitude by amplifying it by -10 db, I found that I would get the original signal back without losing anything (see the waveform below)! This is because Audacity stores the signals in 32-bit floating-point number, and 32-bit floating point number allows a huge range and numbers to be stored, so even when you amplify the signal to a point that there is real, audible distortion, there is no loss in the digital data that represents the signal.


However, you must remember that Audacity project is only a temporary holder for your audio signal. Eventually you will have to convert it to some other formats, and those formats might not be storing data the same way as Audacity does.

To check that, I exported the signal with clipping to WAV format. When I opened/imported the WAV file, I seemed to have the same signal that I saved.


Next I applied the “amplify” effect by -10 db. Note what happened to my signal. The whole signal did get reduced by 10 db, but I did not get my original signal back! The original signal has been lost when I export it to WAV format. The same is also true with MP3 format.


It is useful to know that going over the maximum amplitude does not really cause any harm to our data internally when we work in Audacity (except that there is audial distortion which will affect our editing of the sound). However, signals beyong maximum amplitude might be distorted or forever lost when we save/export to another format.

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