3. Inside an Effects Pedal: Overdrive and Distortion

Now that I have explored the impact that effects pedals have had on guitar playing and popular music I am now going to look inside the pedal and find out a little bit about how they work.  I have decided to look at the distortion and overdrive pedals.  The distortion pedal emulates the sound of a tube distortion using transistors or diodes in the circuitry.  Depending on the material of these diodes and their location within the pedals circuitry a different distorted sound will be produced, because these different diodes will ‘clip’ the input signal wave differently.  Overdrive refers to a much more natural warm sound whereas the distortion pedal is a much harsher, rougher sound.  These pedals affect the guitars input signal by adding overtones which results in a crunchier, warmer sounding guitar.  The distortion effect also works by clipping the sound wave and re-shaping it into a more rigid shape with flat peaks on the sound waves.  A volume boost can also be attained through these pedals.  In terms of affecting the input signal these two pedals work in very different ways.

The difference between the Overdrive and Distortion pedals is the way they clip the sound wave.  Overdrive pedals alter the sound using ‘soft-clipping’.  Soft clipping clips the wave in a much smoother way and avoids harsher clipping which makes the sound wave become more of a square sound wave.  This more rigid clipping is referred to as ‘hard-clipping’ and is used in distortion pedals.  When a sound wave is clipped extra harmonics are added to the input signal and the guitar automatically sounds larger without any boost in the volume.

Overdrive

Now that I have distinguished that the Overdrive pedal gives a much softer distorted tone using soft-clipping I am going to look at the components of the pedal and how important these components are in altering the sound of the guitar.

To replicate the tube distortion of an amplifier, diodes are used in the circuitry of a pedal.  When an input signal is sent through a circuit the entire signal does not come through as audible output, an amount of the signal is sent back through and loops to produce feedback.  The diode in an overdrive pedal is located in this feedback loop and are therefore unable to have an immediate effect on the original signal, the effect they have is somewhat delayed and so when the sound wave is clipped the resulting peak turns out much rounder.  So the location of the diode in the circuitry of the pedal is a very big factor in what kind of clipping it will undertake and what kind of distorted sound that will result in.

Distortion

Distortion pedals work by turning the input signal from the guitar into a square signal.  The distortion is usually activated by a device called a ‘Schmitt trigger’; this trigger generates a square wave at the same frequency as the input of the guitar.  The square wave that is generated is then mixed with the output of the amplified guitar and the ratio of these signals can be altered by the ‘DIST’ knob on the pedal.  If the knob is turned full then more of the clipped signal is allowed through and the final outputted sound will be much distorted.  There is also a level control on many distortion pedals and this controls the gain of the guitar and multiplies the input of the guitar to give it a boost of volume.