Diagram of normal sinus rhythm as seen on ECG. In atrial fibrillation the P waves, which represent depolarization of the top of the heart, are absent.
The wah-wah pedal is based on a simple concept but its effect is far more dramatic. Using a powerful filter to sweep through a broad frequency spectrum, the wah pedal boosts and exaggerates specific tones. Creating sounds that range from thick, flubbery bass to scratchy, stinging treble.
A double bass drum pedal operates much the same way only with a second footplate controlling a second beater on the same drum. Most commonly this is attached by a shaft to a remote beater mechanism alongside the primary pedal mechanism. One notable exception to this pattern is the symmetrical Sleishman twin bass drum pedal.