# Simple Easy Parametric and Graphic EQs Plus Peaks and Notches

Posted on Feb 7, 2014

Everyone is familiar with the sound of a wah pedal. This is a resonant peak in the signal that can get moved around. Not so familiar is a notch, or a sudden reduction in level at one frequency. Sometimes a notch can be very useful in getting a specific sound. Even better would be if you could get either a peak or a notch, depending on how you set the controls - something like the

frequency response diagram. The diagram shows the possible frequency responses of a variable Q peak/notch filter. "Wait a minute! What`s Q " I hear you ask. The techie explanation is that Q is the energy stored divided by the energy dissipated per cycle in a network. Let me translate that into something more useful. A guitar string will vibrate a long time if plucked. The initial pluck that sets it into motion stores a chunk of energy in the string that is saved by the interchange of motion for string stretch on every vibration. It dissipates very little of its energy per cycle, so it stays in motion a long time - it`s a high Q mechanical filter. If you put your finger on the string, it stops ringing very quickly because your finger damps it, removing a lot of energy as the string moves. Your finger has lowered the Q of the vibrating string, removing a lot of energy from it each vibration, so it stops vibrating quickly. Q is also a measurement of bandwidth. Another engineer`s measurement of Q is to divide the center frequency of the filter`s response by the difference between the frequencies where the response is 1/2 of the center response. Q is kind of a measurement of resonance, then. A moderately resonant filter is like a wah pedal - There is a peak of frequency response at the resonant frequency of the wah. To give you an idea about how Q relates to sound, most wahs have a Q of about 2-10. Q is also related to...

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