What is the tuning of DSP？

Many people do not know what is the role of DSP EQ debugging in the end?Today we use the concept of professional audio equipment equalizer to explain what is EQ, in fact, EQ is divided into two kinds (GEQ and PEQ), we will not say complicated today, in the player equalizer setting is we often say EQ.

In the theater, hall, dance hall and other professional audio equipment, in addition to the program source equipment, amplifier, mixer, but also use a lot of signal processing equipment, in order to beautify the sound color, improve the sound quality, enhance a variety of sound effects.Therefore, these signal processing devices are effects in a broad sense.

The so-called signal processing, is the sound signal processing, transformation.In professional acoustics, signal processing or processing mainly has the following aspects.

① Amplitude processing.The equipment that focuses on amplitude processing is compressor, limiter, expander, noise gate, noise reducer and so on.

② Frequency processing.Equipmentfocusing on frequency processing include equalizer, exciter, feedback suppressor, modulator, frequency divider and so on.

③ Time processing.The devices that focus on time processing include retarder, reverberator, etc.

In the signal processing equipment, but also often encountered digital signal processor (DSP), it is the use of digital technology signal processing equipment, can be seen as the description of several aspects of the comprehensive processing, and often in the way of digital program storage.Usually, people are used to refer to the effect is often a reverberator or digital signal processor.

Function and type of frequency equalizer

Frequency equalizer is widely used in hall amplification, and its main functions are as follows

① The correction of frequency distortion caused by audio equipment can not only compensate for the lack of frequency components in various program signals, but also suppress the excessive frequency components.

② Correct the frequency distortion caused by indoor acoustic resonance characteristics to make up the structural defects of architectural acoustics.

③ Restraining sound feedback and improving the quality of hall sound amplification.

④ To improve the sound quality and acoustics by modifying or beautifying the tone.

For example, in the hall sound reinforcement system after the installation, because the hall acoustic resonance and the amplification system (including microphone, amplifier, speakers, the transmission properties of the room) frequency characteristic curve of the ups and downs is very big, then can use frequency equalizer equalizer (room), through ascension (or attenuation) caused by hall of certain frequency of valley point (or the peak point),The overall response characteristics are flattened ten times, which is called mirror equilibrium.For the sound amplification system with acoustic feedback, the maximum gain can only be so large that the maximum peak point in the frequency response curve is close to the point of self-excitation if the system is to be stabilized before equalization.At this time, except for the narrow frequency band near the maximum peak point, the amplification gain in the human part of the frequency band is very low, which often cannot meet the requirements of use.With the help of frequency equalizer, the large peaks are eliminated and the frequency characteristics become uniform, so that the amplification gain of all frequency points has been greatly improved.As for the use of frequency equalizer to modify the tone, improve the quality of sound is well known. 

The main technical indexes of equalizer

Frequency points (number of segments)

The center frequency setting of the equalizer, as mentioned above, has certain regularity, such as octave, 1/2 octave and 1/3 octave, etc.In general, the more frequency points, the narrower the band width and the higher the Q value.

Balance

Namely control range, it refers to the equalizer to the center frequency of the signal corresponding to the maximum amount of promotion or attenuation, commonly used decibels.Its specifications are ±6dB, ±12dB, ±15dB, ±18dB and so on.The higher the value is, the stronger the control ability is.

Harmonic distortion

It is generally required that the harmonic distortion should not be greater than 0.1%.

Equivalent input noise level

This is the index corresponding to the signal-to-noise ratio.The smaller the value, the better the SNR.It is usually required that the equivalent input noise should not be greater than -90dB.

The Q value and center frequency adjustment range of the parametric equalizer

Q value is also called quality factor.The higher the Q value, the sharper the equalizer lift or decay curve, and the narrower the bandwidth (frequency band width);Conversely, the lower the Q value, the wider the bandwidth.The Q value is usually adjusted between 0.3 and 20.The center frequency adjustment of the parametric equalizer can be varied within a certain range.In general, the more frequency points are divided, the smaller the corresponding center frequency range and the larger the Q value, and there should be transitional (or intersecting) frequency points between each frequency band.

The use of the equalizer

The application of equalizer can beautify the sound quality of human voice or musical instrument, so the correct use of equalizer is very important.In order to use the equalizer correctly, it is necessary not only to master the performance and characteristics of all kinds of equalizer, but also to be familiar with the sound quality characteristics of each frequency band of audio, as well as the basic frequency range of various sound sources.Different frequency bands of the equalizer have different effects on the sound quality or hearing sensation.According to the experiment and people's experience, the corresponding frequency band and hearing sense can be generally divided into the following six parts.

16 ~ 60Hz(ultra low tone)

Elevating this band gives a powerful feel.Raise below 20Hz, can increase (such as DISCO) air vibration sense;Raising 60Hz can strengthen the strength of the sound and give people a sense of shock, but too much lifting will make the sound of the instrument cloudy and unclear.

60 ~ 250Hz(bass)

Rhythm The basic sound of a part that determines the balance of the music, giving it fullness or thinness.There will be a "rumble" when you lift too much.Raising 100Hz can produce a realistic double bass playback effect.But for speech sound, attenuation of 6 ~ 12dB below 100Hz can increase the articulation of speech.The frequency band between 100 and 250Hz affects the fullness of the sound, but too much will make the music muddy and increase the feeling of fatigue.

250Hz ~ 2KHz (medium tone)

Contains the lower harmonics of most instruments, affecting timbre.1 ~ 1.5KHz increased by 4 ~ 5dB, the brightness and level of the sound were improved, and the timbre was bright and smooth, especially for the male voice.Among them, raising 300 ~ 500Hz can increase the strength of music and make the restored human voice more realistic. In particular, 330Hz can give people a solid sense of sound and make the bass soft and plump.However, if 330Hz is raised too much, it will produce a "buzzing" "bathroom effect".500Hz has a great influence on the strength. Increasing it by 2 ~ 4dB is like speaking in front of the listener, which gives people a sense of intimacy and depth.Raise 1000-2000Hz, will emit metal sound.

2 -- 4KHz (medium to high pitch)

It is the sensitive hearing range of the human ear and has the greatest impact on the brightness of the sound. The increase of 2-4dB in this section can increase the brightness of the human voice. However, if the increase is too much, especially at 3000Hz, it will produce auditory fatigue and damage the sense of hierarchy of medium and high frequencies. 

4 ~ 6KHz (high pitch)

This frequency band is a telepresence segment, which can increase the clarity of language and musical instrument sound.Appropriately raising the frequency band can make the sound bright and prominent, which is conducive to improving the clarity and richness of the sound.4.5kHz has penetrating power.If there is obvious attenuation above 5 ~ 6KHz, the voice will be dark and dumb without color.The frequency band produces an intolerable cacophony over time.

6 ~ 16KHz (extra high pitch)

This frequency band can control the overall brightness and clarity of sound, especially at 12kHz, but too much emphasis on this frequency can cause speech to produce dental sounds.The frequency band is raised too much, easy to produce hiss, make the sound harsh.

In short, if the listening sensation of the whole sound frequency band is divided into three segments, the low frequency band focuses on the richness and fullness, the middle frequency band focuses on the brightness, and the high frequency band focuses on the clarity.Equilibrium frequencies of some common instruments and sounds are shown in the table.

The above introduction is mainly in the recording, tuning or program recording of the equalizer use methods, the following introduction of equalizer in listening to sound and the use of sound.Due to the development and popularity of home theater and combination sound, the equalizer originally used for professional sound (such as picture equalizer) is also widely used in home theater, recorder and combination sound.The use of an equalizer or a multi-frequency tone controller for listening and pealing is generally shown below.

①When listening to AM radio, due to the narrow frequency band of AM radio, its high frequency can only be transmitted to 5 ~ 6KHz at most, so appropriately attenuating the frequency component below 100Hz and above 6KHz can improve the signal-to-noise ratio.

②When listening to FM radio, due to the frequency band width and high signal-to-noise ratio of the FM radio program, at this time, the push buttons of each frequency band of the diagram equalizer should be placed in the center of the flat position or the high and low frequency should be appropriately promoted to give full play to the characteristics of good sound quality of FM radio. 

③When playing music programs (such as orchestral music), low frequency (such as 60Hz or 100Hz) and high frequency (such as 10KHz or 15KHz) can be promoted to the maximum, LKHz medium frequency point does not increase or attenuate slightly, and 300-500Hz and 3 ~ 5KHz to raise some appropriate.From the graph of pushing buttons on the panel, the push button of the multi-band icon equalizer is in the shape of "V", so that the music released is distinct, the sound is bright, and the bass is full. 

④When playing solo and chorus songs, the high frequency end can be placed in the middle position, and the frequency band of 3 ~ 5KHz will attenuate slightly, the frequency band of 100Hz and 1000Hz will increase slightly, and the frequency band of 300Hz will increase to the maximum. In this way, the basic part of the song can be highlighted, and the song will sound more powerful and clear.In order to make the singer's tonic clear, the main frequency is around 1000Hz, which can give the tonic a sense of depth. 

⑤When playing language programs, the adjustment is generally opposite to that when playing music programs, that is, the frequency band of 1000Hz is promoted, the frequency band of 300-500Hz and 3-5kHz is promoted properly, the low frequency band and high frequency band are generally not promoted or slightly attenuated, that is, it shows an inverted "V" shape from the graph formed by the buttons on the panel.This is because the frequency spectrum of language is concentrated in 300 ~ 4000Hz, so the adjustment of interpretation can improve the articulation of speech and make the background appear quiet. 

⑥When playing a tape program, the graphic equalizer is usually placed in a flat position, or the high-frequency and low-frequency components are appropriately raised.If the tape noise is obvious, the high frequency band can be appropriately reduced to reduce the background noise of the tape. 

Of course, above adjustment sees the content of the program even and the interest of each one and decide, the compensation of the acoustical characteristic that considers acoustical equipment and sound box and listens to sound room environment even in addition.