What is Diode Clipping? | Too Afraid To Ask

it’s time to learn about clipping…

Dirt pedals generate their drive in a two stage process: Firstly they use amplification to increase the signal gain, and then clipping diodes carve up the waveform generating distortion.

While it’s common for clipping to begin in the op amp, where the gain level applied takes the signal voltage beyond what the amplification chip can cleanly reproduce, it’s the secondary process, diode clipping, which is the focus of our attention in this Too Afraid To Ask video.

We will use Walrus Audio’s Ages Overdrive as an example as it features 5 different gain and clipping modes allowing a variety of different drive flavours, which makes it an excellent scientific test subject.

Semiconductor diodes like those used for clipping in Ages, are small electronic components which only conduct when certain conditions are met.
The diode’s Forward Voltage is the voltage at which the diode begins to pass current, and while we won’t get into the intricacies of semiconductor physics to explain exactly how that works, we can explain why it’s an incredibly useful property which is exploited in overdrive pedals.

Carefully placing diodes in the audio signal path will allow signals up to a certain voltage to pass without being altered. However any high voltage parts of the signal (which relate to loud parts of the signal) will exceed the Forward Voltage of the diodes, allowing the diode to begin conducting, carrying the excess voltage away from the signal.

This leaves a waveform that looks like it has had its top shaved off, clipped, producing a lot of high order harmonic content which we hear as distortion.

The video above goes further into explaining different arrangements of clipping diodes, as well as the difference between silicon and LED clipping.