Alesis Q20 Equalization

Chapter 3 - Overview

Equalization

Equalization, or EQ, provides the ability to control the timbre, or coloration, of an audio signal by changing the frequency response of a Q20 audio path. Filters and EQ can be used to compensate for frequency deficiencies in microphones and other sound equipment. The EQ family of functions in the Q20 contains filters, equalizers, and several other highly useful studio effects.

Filters

Lowpass, Bandpass, and Highpass

A filter allows the passing of frequencies within a certain range (called a filterÕs passband), and removes frequencies outside that range. The Q20 features a Lowpass Filter, which removes frequencies above its cutoff frequency (i.e., it allows low frequencies to pass through), and a Highpass Filter, which removes frequencies below its cutoff frequency. At the cutoff frequency, each filter attenuates the signal level by -3dB, and attenuates by 6dB per octave outside the passband. The Bandpass Filter passes frequencies near its center frequency, and removes all others. The Bandpass Filter has a bandwidth parameter to control how wide (in octaves) the passband is. Bandwidth is inversely related to the conventional ÒQÓ value; that is, the higher the Q value, the lower the bandwidth. Bandwidth is used in the Q20 because it is a more familiar term to many musicians, and is more intuitive.

	Cutoff Frequency		Cutoff Frequency
0dB		0dB
-3dB		-3dB

Level	Frequency	Level	Frequency
	Lowpass Filter		Highpass Filter
	Center Frequency		Center Frequency
0dB		0dB
-3dB		-3dB
	Bandwidth			Bandwidth
Level	Frequency	Level	Frequency
	Bandpass Filter		Bandpass Filter
	(low bandwidth)		(high bandwidth)

32 Q20 Reference Manual