Overdrive is a gain-based effect commonly mistaken with a distortion effect. It occurs when input gain surpasses the capacity of a device to handle the amount of gain it receives. When the device in question is a tube, the smooth waveform that goes into the device gets clipped. Therefore, we perceive this clipping as a distortion. The higher the amplitude of the wave, the greater the distortion we perceive. As you can perceive, the former and the latter one are almost identical. The confusion is most clearly exemplified when talking about guitar effect pedals.
Overdrive vs Distortion
Overdrive happens in the front-end (what you put in), whereas distortion occurs in the back-end (what you hear). When we refer to overdrive as simply overpowering, the front-end of an amplifier to make the tubes clip, the only pedal that is an overdrive is a boost pedal. This pedal enhances the guitar’s signal and ups its voltage. Many manufacturers refer to this as overdrive pedals, but technically they are distortion pedals. All in all, one associates the effect with amp distortion because it tries to simulate the effect of amp tubes being overdriven by high gain.
Overdrive Guitar Pedals
These pedals fall into two categories: transparent mid-scooped boosters, and compressed boosted overdrives. The transparent mid-scooped boosters drive large tube stacks into distortion. They sound creamy and smooth on a compressed and mid boosted Marshall, but sound terrible on an uncompressed. In contrast, compressed and mid boosted overdrives produce a smoother and bigger sound tone on amplifiers such as the Twin and smaller bedroom amps.
In Brief
Overdrive is generally a milder and less linear distortion with a more dynamic response. The tones tend to saturate less when played more quietly, but they will distort more when played louder or harder. When the tone starts to overdrive, the signal is soft-clipping. As a result, the signal is distorted. It becomes turns out as a smooth compression and it is progressive according to how much it has crossed the limit.
