The use and function of several major equipment in professional audio equipment

　　In professional audio systems, speakers and power amplifiers are commonplace, but there are also some peripheral devices that are necessary, but few people pay attention to these details, then GAEPro audio editor will take you to know them.

　　1. Frequency divider - The frequency divider refers to distinguishing the sound signals of different frequency bands, amplifying them respectively, and then sending them to the speakers of the corresponding frequency bands for playback. Electronic crossover processing is required for high-quality sound reproduction.

　　It can be divided into two types: (1) Power divider: located after the power amplifier, set in the speaker, through the LC filter network, the power audio signal output by the power amplifier is divided into bass, midrange and treble, which are sent to the respective speakers. The connection is simple and easy to use, but it consumes power, appears audio valley, and produces crossover distortion. Its parameters are directly related to the impedance of the speaker, and the impedance of the speaker is a function of frequency, which deviates greatly from the nominal value, so the error It is also larger, which is not conducive to adjustment. (2) Electronic frequency divider: The equipment that divides the weak audio signal is located in front of the power amplifier. After frequency division, each independent power amplifier is used to amplify the signal of each audio frequency band, and then send it to the corresponding speaker. unit. Because the current is small, it can be realized by an electronic active filter with low power, which is easier to adjust, reduces power loss, and interference between speaker units. The signal loss is small and the sound quality is good. However, this method uses an independent power amplifier for each channel, which has high cost and complex circuit structure, and is used in professional sound reinforcement systems.

　　2. Exciter - Exciter is a harmonic generator, a sound processing device that uses human psychoacoustic characteristics to modify and beautify sound signals. By adding high-frequency harmonic components to the sound and other methods, it can improve the sound quality, timbre, improve the penetration of the sound, and increase the sense of space of the sound. Modern exciters can not only create high-frequency harmonics, but also have functions such as low-frequency extension and musical style, making the bass effect more perfect and the music more expressive.

　　Improve the clarity, intelligibility and expressiveness of your voice with exciters. Make the sound more pleasing to the ear, reduce listening fatigue, and increase loudness. Although the exciter only adds about 0.5dB of harmonic content to the sound, it actually sounds like the volume has increased by about 10dB. The auditory loudness of the sound is significantly increased, the stereoscopic effect of the sound image, and the separation of the sound are increased; the positioning and layering of the sound are improved, and the sound quality of the playback sound and the reproduction rate of the tape can be improved. High-frequency noise occurs because the acoustic signal loses high-frequency harmonic components during transmission and recording. At this time, the former uses an exciter to compensate the signal first, and the latter can filter out the high-frequency noise with a filter, and then create a high-pitched component to ensure the playback quality. The adjustment of the exciter requires the sound engineer to judge the sound quality and timbre of the system, and then adjust it according to the subjective listening evaluation.

　　3. Equalizer - Equalizer is an electronic device that can separately adjust the amount of electrical signal amplification of various frequency components. It compensates for the defects of speakers and sound field by adjusting the electrical signals of various frequencies, and compensates and modifies various electrical signals. Sound source and other special functions, the equalizer on the general mixer can only adjust the electric signals of high frequency, intermediate frequency and low frequency respectively.

　　Equalizers are divided into three categories: graphic equalizers, parametric equalizers, and room equalizers.

　　1. Graphic equalizer: also known as graphic equalizer, through the distribution of push-pull keys on the panel, the adjusted equalization compensation curve can be directly reflected, and the boost and attenuation of each frequency are clear at a glance. It adopts constant Q value technology. There is a push-pull potentiometer at each frequency point, no matter whether a certain frequency is boosted or attenuated, the frequency bandwidth of the filter remains unchanged. The commonly used professional graphic equalizer is to divide the 20Hz~20kHz signal into 10, 15, 27, and 31 segments for adjustment. In this way, people choose frequency equalizers with different numbers of segments according to different requirements. Generally speaking, the frequency points of a 10-band equalizer are distributed at octave intervals. In general, a 15-band equalizer is a 2/3-octave equalizer. When used in professional sound reinforcement, a 31-band equalizer is 1 /3-octave equalizer, most of them are in the more important occasions that need fine compensation, the graphic equalizer is simple in structure, intuitive and clear, so it is widely used in professional audio.

　　2. Parametric equalizer: also known as parametric equalizer, an equalizer that can finely adjust various parameters of equalization adjustment. It is mostly attached to the mixer, but there are also independent parametric equalizers. The adjusted parameters include frequency band, Frequency point, gain and quality factor Q value, etc., can beautify (including ugliness) and modify the sound, making the sound (or music) style more distinctive and colorful to achieve the desired artistic effect.

　　3. Room equalizer, an equalizer used to adjust the frequency response characteristic curve in the room, due to the different absorption (or reflection) amount of decorative materials for different frequencies and the influence of normal resonance, resulting in sound coloration, room equalizer must be used. Objectively compensate and adjust the frequency defects due to sound construction. The finer the frequency band is, the sharper the adjustment peak, that is, the higher the Q value (quality factor), the more detailed the compensation during adjustment, the coarser the frequency band, the wider the adjustment peak, when the sound field transmission frequency characteristic curve is more complex difficult to compensate.

　　4. Compression Limiter - Compression limiter is a general term for compressor and limiter. It is a processing device for audio signals, which can compress or limit the dynamics of audio electrical signals. The compressor is a variable gain amplifier, and its amplification factor (gain) can automatically change with the strength of the input signal, which is inversely proportional.

　　When the input signal reaches a certain level (the threshold value is also called the critical value), the output signal increases with the increase of the input signal, which is called Compressor; if it does not increase, it is called Limiter. In the past, the compressor used a hard knee (Hard-knee) technology, once the input signal reached the threshold. The gain is immediately reduced, so that there will be a dynamic sudden change of the signal at the inflection point (the turning point of the gain change), so that the human ear can clearly feel that the strong signal is suddenly compressed. In order to solve this problem, the modern new compressor adopts the soft-knee technology. The compression ratio change of this compressor before and after the threshold is balanced and gradual, making the compression change imperceptible, and the sound quality is further improved. .

　　The compressor can keep the volume of the instrument and the singer in a certain balance during the recording process; ensure the balance of various signal strengths. Sometimes it is also used to eliminate the vocalist's articulation, or to change the compression and release time to produce a "reversed sound" special effect where the sound changes from small to loud. In broadcast systems, it is used to compress program signals with a larger dynamic range, and to improve the average transmission level on the premise of preventing modulation distortion and preventing overloading of the transmitter.

　　In the sound reinforcement system of dance halls, the compressor is used to compress the signal to maintain the original program and reduce the dynamics of the music to meet the requirements of the sound reinforcement system and artistic activities. While compressors serve a variety of purposes, modern compressors commonly employ new technologies such as soft knees that further reduce the compressor's impact on the compressor.

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