Equalizers and their application
Graphic equalizer is a multi-range corrector of the amplitude-frequency characteristics of electric sound signals. The boundaries of the full range of frequencies in which the amplitude-frequency characteristic is corrected are determined by the range of frequencies perceived by the human ear. The lower limit of this range is sound vibrations with a frequency of 20 Hz. (oscillations per second), and the upper – 20 KHz. (thousand oscillations per second).
The graphic equalizer, depending on its accuracy, determined by the width of one band, may contain a different number of ranges in which the values of the amplitude-frequency characteristics are set. For example, with a bandwidth of one octave, the equalizer will contain 10 bands, with a bandwidth of 1/2 octaves – 15 bands, and with a bandwidth of 1/3 octave – 31 bands. The greater the number of bands the equalizer contains, the more accurately its transfer amplitude-frequency characteristic can be selected, and, consequently, the amplitude-frequency characteristic of the output signal of the equalizer.
The third-octave equalizer can have not 31, but 30 bands in which the signal amplitude is corrected. Such an equalizer has a slightly reduced frequency range. Usually, there is no range with a frequency of 20 Hz, and a regulator with a frequency of 25 Hz changes the level of all those frequencies that lie below 25 Hz. The 27-band equalizer may not have bands with frequencies of 20, 25, 31.5 Hz and 20 kHz.
We will consider various functions of the equalizers using the full 31-band graphic equalizer as the main functions of this equalizer are often found in other types of equalizers.
Frequency Response Adjustment Range
Numerical values indicating the adjustment range of the graphic equalizer indicate how many decibels the signal level in any of its frequency bands can be increased or decreased. The central position of the level knobs corresponds to 0 dB, so the full range of equalizer adjustment will be determined by the maximum deviation of the knob from this position up or down. This range can be ± 12 or ± 15 dB. For fine tuning, this equalizer with the help of a special switch can be reduced to ± 6 dB, which is convenient when tuning the sound of the path of sound reproduction systems.
The use of equalizers (Equalizers and their use)
High pass filter
This filter is sometimes called a low-cut filter. With the introduction of such a filter into the circuit, it greatly attenuates the sound of frequencies lying in the range below 30 – 40 Hz. On some types of graphic equalizers, in addition to the switch on this filter, a separate attenuation level control is also provided, which allows you to set the slope slope.
Low pass filter
This filter is also sometimes called a high-pass filter. It is designed to attenuate frequencies in the range of 8-10 kHz and higher. The low pass filter can also be controllable and have a variable cutoff frequency.
When bypass is turned on, the sound signal from the equalizer input is sent directly to its output, bypassing the correcting circuits. This function is convenient to use when setting up the equalizer to compare the original signal with the adjusted one.
When the overload indicator is lit, it indicates that there is overload distortion in the output signal caused by the input voltage being too high. In case of overload, it is necessary to reduce either the level of the signal supplied to the equalizer input or its sensitivity.
Band Level Controls
Using the band level controls, the spectral components of the audio signal are amplified or attenuated in the range of the selected frequency band by the amount indicated next to the control knob. Setting a level requires careful attention. Excessive attenuation of the spectral components causes a frequency dip and the sound becomes dead. Excessive rise causes a frequency peak and the signal in the corrected section of the spectrum begins to ring.
Equalizer output level control
Equalizer output level controls adjust the level of its output signal. The maximum positions of these controllers are usually associated with a gain level of +6 dB, although it may be more. With the help of output level controllers, they resort, if necessary, to compensate for the attenuation of the average signal level caused by the weakening of its spectral components, and vice versa.
The operation of this type of equalizers was partially already described in the description of the principle of operation of the quasi-parametric equalizer of the input channels of the mixing consoles. It remains to add to the above that the parametric equalizer, as a separate device, should be complete, that is, it should cover the entire range of sound frequencies by adjustment and allow all three parameters of the tunable filters of which it consists to be set.