The Role and Type of Frequency Equalizer

- Aug 20, 2018-

In professional audio equipment such as theaters, halls, dance halls, etc., in addition to program source equipment, amplifiers, mixers, many signal processing equipment is used to enhance the sound, improve the sound quality, and enhance various sound effects. Therefore, these signal processing devices are broadly referred to as effects.

The so-called signal processing is the processing, transformation, and the like of the sound signal. In professional audio, signal processing or processing mainly has the following aspects.

1. Amplitude processing. Devices that focus on amplitude processing include compressors, limiters, expanders, noise gates, noise reducers, and the like.

2. Frequency processing. Devices that focus on frequency processing include equalizers, exciters, feedback suppressors, transposes, frequency dividers, and the like.

3. Time processing. Devices that focus on time processing include delays, reverberator, and the like.

In signal processing equipment, a digital signal processor (DSP) is also often encountered, which is a signal processing device using digital technology, which can be regarded as a comprehensive processing of several aspects, and is often stored in a digital program. Usually, people commonly used to refer to the effector often refer to the reverberator or digital signal processor.

The role and type of frequency equalizer:

The frequency equalizer is widely used in the hall sound reinforcement, and its main functions are as follows.

1. Correcting the frequency distortion generated by the audio equipment can not only compensate for the missing frequency components in various program signals, but also suppress the excessive frequency components.

2. Correct the frequency distortion generated by the acoustic resonance characteristics of the room to compensate for the structural defects of the building acoustics.

3. Suppress acoustic feedback and improve the quality of hall sound reinforcement.

4. Modify or beautify the sound to improve sound quality and sound.

For example, after the hall sound reinforcement system is installed, the frequency characteristic curve of the sound reinforcement system (including the transmission characteristics of the microphone, amplifier, speaker, and room) fluctuates greatly due to the acoustic resonance of the hall. At this time, the frequency equalizer (room equalizer) can be used, by raising (or attenuating) the valley point (or peak point) caused by the hall to certain frequencies, so that the total response characteristics are flattened, which is called mirror equalization. For a sound reinforcement system with acoustic feedback, before the equalization process, the sound reinforcement system should be stabilized, and the maximum gain can only be so large that the maximum peak point in the frequency response curve is close to the self-excitation. At this time, except for the narrow frequency band near the maximum peak point, the sound amplification gain in the human part of the frequency band is very low, and often cannot meet the use requirements. After processing by the frequency equalizer, the large peaks are eliminated, the frequency characteristics become uniform, and the sound amplification gain of all frequency points is considerably improved. As for the use of a frequency equalizer to modify the tone and improve the sound quality is well known.

Equalizer curve.jpg

The equalizer can be divided into four types according to the frequency characteristic shape, as shown in the figure. Figure (a) shows the frequency characteristics of a Shelving equalizer. These equalizers, also known as rack equalizers, are used to boost or attenuate high and low frequencies over a wide frequency range, so-called Tone control. Its characteristics change more gently, not suitable for fine adjustment of the tone. The basic form of the Presence type equalizer is a single-peak resonance characteristic used to boost or attenuate a certain frequency band. Usually, several resonant frequencies are used, as shown in (b), which can be used to perform finer sounds adjustment. Figure (c) shows the frequency characteristics of the equalizer. Its panel is equipped with a row of push-pull potentiometers, each potentiometer corresponding to a center frequency. The entire audio range (from low frequency to high frequency) is generally divided into 9-31 center frequencies, and its adjusted frequency response curve can be visually displayed from the position where the push-pull potentiometer push rod is located, so it is called a graphic equalizer.

The above equalizers all have a fixed center frequency and adjust the amplitude of the boost or attenuation of each point. There is also an equalizer, as shown in (d), the center frequency, the Q value (corresponding to the bandwidth of the center frequency) and the lifting (or attenuation) amplitude are respectively adjustable, so it is called a parametric equalizer. . This parametric equalizer has fewer frequency points, but it can easily and accurately perform equalization of various holiday signals over the entire audio range. It can also be used to significantly enhance certain frequency bands to form special acoustic effects, or a certain frequency point is greatly suppressed to filter out specific interference or noise, and the useful signal is lost as little as possible. Recently, a parametric equalizer or a semi-parametric equalizer has been widely used in the mixer.



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