Equalizer

The story of equalizers began in the 1930s in Hollywood , when the first films with sound appeared. At that time, many paid attention to the unnatural sound of music and the voices of actors. One of these people was John Wolfman, who used the first equalizer to improve the sound of sound systems in a movie theater. Prior to this, equalizer-like devices were used to correct sound loss during signal transmission. However, Volkman was the first to introduce an equalizer into a sound reinforcement system. The first such equalizer (EQ-251A) was a device with two sliders, each of which had a frequency selection switch.

At the same time, experiments were conducted with equalizers in Hollywood recording studios in order to post-production and create effects. Then Cinema Engineering developed the first true graphic equalizer (model 7080), which had 6 bands, adjustable within 6 dB in 1 dB steps, and subsequently the very popular 7-band equalizer 9062A at that time.

During the Second World War, there was a lull in this area, and in 1958, Wayne Radmouth University professor successfully developed and applied his theory of acoustic equalization. After that, in 1962, Radmouth, together with his friend Bouner, developed an acoustic filter with a very high Q factor - this was how the White equalizer was developed, which helped Bounder to create a theory of acoustic feedback and room equalization.

In 1967, Art Davis (of Cinema Engineering), together with Jim Noble and Don Davis, developed the first set of passive 1/3-octave filters, which was called "Acousta-Voice". This system marked the beginning of a new era of modern equalization.

Over the next 20 years, there has literally been a boom in the development of equalizers: a wide variety of equalizers have been created, using microchips and other digital technologies.

There are two main types of multi-band equalizers: graphic and parametric . The graphic equalizer has a certain number of frequency bands adjustable in level, each of which is characterized by a constant working frequency, a fixed band width around the working frequency, and also a level adjustment range (the same for all bands). As a rule, the extreme bands (the lowest and highest) are “shelf” type filters, while all the others have a “bell-shaped” characteristic. Graphic equalizers used in professional areas usually have 15 or 31 bands per channel, and are often equipped with spectrum analyzers for easy adjustment.

The parametric equalizer provides much greater possibilities for adjusting the frequency response of the signal. Each strip has three main adjustable parameters:

• Central (or working) frequency in hertz (Hz);
• The quality factor (the width of the working strip around the center frequency, is indicated by the letter "Q") is a "dimensionless" value;
• The gain or attenuation level of the selected band in decibels (dB).

Thus, the user can more accurately select the desired frequency and adjust it more precisely. Analog parametric equalizers are quite rare and have a small number of adjustable frequency bands. However, advances in digital processing of the audio signal contributed to the emergence of digital parametric equalizers with an almost unlimited number of adjustable frequency bands. Very often, parametric equalizers can serve as one of the processing units of digital acoustic processors . Moreover, in digital parametric equalizers there are often additional band parameters, such as: filter type, curve nature, etc.

There are mixed-type equalizers that can be found in mixing consoles, where, for example, low and high frequencies are regulated by the type of graphic equalizer of the “shelf” type, and between them there are two semi-parametric bands (without Q adjustment).

There are also hybrids called "paragraphic" - it is a graphic type equalizer with Q-factor adjustment.

When working with the equalizer, it is very important to understand that amplification of a frequency band leads to an increase in the overall level of the audio signal and excessive amplification of the bands can often lead to distortion of the audio signal. In this regard, the weakening of the "unnecessary" frequencies often gives a better result than the amplification of the "necessary". Therefore, the equalizer should be used very carefully and not used if there is no obvious need for it.

Equalizers have a wide range of applications. Their main purpose is to obtain an adequate (linear) sounding of the source material, the frequency response of which may be distorted due to deficiencies in speaker systems, inter-unit processing devices, room parameters, etc.

Often equalizers are used in the lines of stage monitors, the main problem of which is the occurrence of the “ feedback ” effect. In this case, the sound engineer uses a multi-band graphic equalizer to search for the resonant frequency and its attenuation. In addition, using the equalizer, you can limit the frequency range of sound reproduction. However, not all experts use graphic equalizers to eliminate feedback, since there are special devices for this - digital automatic feedback suppressors, which, in essence, are a parametric equalizer with automatic selection of the resonant frequency, and their filters have a very high Q factor.

Many musicians during recording or performances use various equalizers to get the unique sound of their instruments , as well as special effects associated with the bright highlighting of specific frequency bands. For example, removing all low and high frequencies with an equalizer, leaving only the middle range, you can get the effect of the “old radio”. Almost all DJs during the sets actively use equalizers on mixing consoles, again to create certain effects.

Another fundamental application of the equalizer is the frequency correction of sound reproduction of stationary sound amplification systems depending on the acoustic parameters of the room. The frequency response of sound is influenced by many factors: the size and shape of the room, wall coverings, the number of spectators in the room and much more - all this can greatly change the frequency response of the reproduced material. In this case, specialists use three main components: a high-precision measuring microphone , a spectrum analyzer and an equalizer. All this allows them to find out which frequencies "disappear" in a given room and which are allocated, and in accordance with this, make a correction.

In recording studios, equalizers in the form of separate devices are used infrequently. This is due to the fact that modern studios are equipped with equipment that practically does not distort the frequency response of the recorded material. However, with digital mixing and mastering, almost all tracks “pass through” the software equalizer, but, as a rule, in order to remove or attenuate unnecessary frequencies that can interfere with the purity of the resulting mix. This is especially true for the voice (vocals), which has a fairly narrow frequency range, as well as some disadvantages that may be associated with articulation and manner of performance.

As a rule, feedback suppressors are multi-band equalizers with the function of automatically determining the “problem” frequency and changing its volume. Suppressors can work in different modes and solve a problem differently.
Example: feedback occurs at a frequency of 1500 Hz. In automatic mode, the device continuously scans the entire frequency spectrum of the signal for feedback, finds it at a frequency of 1.5 kHz, then attenuates the volume level of this frequency to the optimal state and remembers this frequency. After that, feedback at 1.5 kHz no longer appears.

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• Equalization (audio) (English)