Control Techniques of Frequency Equalizer
The equalizer (EQUALSER) is an electroacoustic processing device that adjusts the frequency response and amplitude of the acoustic signal. It can change the ratio of sound to harmonic components, frequency response characteristic curve, frequency bandwidth, etc. Frequency equalizers are widely used in various audio systems, such as hall amplification and playback systems, broadcast recording systems, and home audio systems. It plays a broad role in beautifying the sound in recording (referring to simultaneous recording and multi-track pre-recording) and post-processing (referring to second-order equalization of ready-made recording programs and multi-track recording post-production). For example: (a) make up for the defects of frequency response; (b) make up for the defects of sound quality and timbre; (c) highlight the characteristics of the instrument or change the timbre of the instrument; (d) balance the loudness of each part in the band; (e) improve the music Fullness, brightness and clarity; (f) Increase presence, adjust playing levels; (g) Alleviate crosstalk between parts, attenuate leakage frequency; (h) Remove noise and interference sounds, improve signal-to-noise ratio; (I ) Fix the frequency response defects in the listening environment and equalize the indoor frequency response? It can be said that the equalizer is the most important tuning tool in the work of sound engineer and sound engineer. It is also the most important tool for our voice workers to improve voice timbre.
A brief introduction to the characteristics of equalizer types
No matter what kind of equalizer, its function is to adjust the frequency response (AUDIO RESPONSE) of the amplifier through the audio frequency (AUDIO FREQUENEY) filtering process. This adjustment can make the loudness of certain frequencies greater or less than the sounds of other frequencies, and the method of raising or attenuating the level of a certain frequency by a few decibels is called EQUALSATIOM (EQ). There are two ways for the equalizer to boost the frequency (BOOS) attenuation (FADE): one is the shelf-shaped method (SHELVING); the other is the peak-valley method (PEAK SLAP AND DIP). The names of these two methods are named after the shape of the frequency response curve for the frequency increase and attenuation (there is another classification is divided into graphic equalizer and parametric equalizer). Below we discuss these two methods further.
The so-called shelving method actually divides the signal, and part of the frequency passes directly, and the other part of the frequency (height or low frequency band) is attenuated, so as to achieve a relative increase or attenuation of a certain frequency in the sound, forming a frequency response The shape of the frame. This method is mostly used by high-pass filter (HIGHT PASS FILTER) and low-pass wave filter (LOW PASS FILTER), the difference is that the attenuation outside the high-pass wave filter pass band (PASS BOND) is not balanced, To be precise, its attenuation increases continuously.
High-pass filter and low-pass as their name implies, some frequencies pass straight through, while others are attenuated. The frequencies with attenuation less than 3dB are the passband frequencies, and those with attenuation exceeding 3dB are the frequencies within the stopband. They have a power of 1/2 the passband power. The frequency at which the signal attenuation is exactly 3dB is the cutoff frequency or crossover frequency. The attenuation of the stop band outside the cut-off frequency is generally attenuated by an equal decibel value per frequency band. The ratio of this attenuation is called the slope (SIOPE). For example, the commonly used attenuation slope is 12dB, 15dB, 18dB and other parameters per frequency range. The cut-off frequency of the high-pass filter is generally between 20 Hz and 250 Hz. The cut-off frequency of the low-pass filter is generally between 6KHz and 12KHz. Generally, the high and low pass filters can be installed on a dedicated equalizer as an auxiliary function for gating frequency characteristics or filtering high and low frequency noise. If the high-pass filter and the low-pass filter are used for attenuation at the same time, and the intermediate frequency band is output straight (FATTENS OUT), then a band pass filter (BAND PASS FILTER) is formed. The bandwidth of the passband of this filtering method is controlled by the cutoff frequency of the high and low pass filters, and the Q value is controlled by the attenuation slope of the high and low pass filters. The frequency response curve of this band-pass filtering method can be flexibly adjusted and can be made very wide.
The simple peak-valley mode is generated by the LC circuit (that is, the circuit composed of the inductor and the capacitor). In the filter circuit, when these two reactive components are connected in series, they will exhibit the minimum impedance for a certain frequency, while for other frequency bands. The signal is very impedance. The frequency with low impedance is called the center frequency (CENTER FREGUENCY) or resonance frequency.
Connect a variable resistor in series with the LC circuit, and then parallel it with another fixed resistor. The signal away from the center frequency passes through the R circuit and is greatly attenuated. At the far end of the fixed resistor, two lines carrying different frequencies are combined, then we can imagine that the center frequency of the LC circuit can get a very high level due to the small attenuation, and the other frequencies through the R circuit are due to the large attenuation. When the level is lowered, the peak shape of a certain frequency is increased, and the degree of increase depends on the resistance of the resistor. If the R circuit is grounded and the LC circuit is bypassed into the ground, the center frequency will be greatly and infinitely attenuated, so that the attenuation of other frequency levels is very small, which will cause a valley-shaped attenuation of a certain frequency. The degree of attenuation depends on the resistance value. The peak-valley mode is mostly used for graphic equalizers and parametric equalizers. The EQ in COOL EDIT is such an EQ.
The equalizer (GRAPHIC EQUALISER) divides the full audio frequency (20Hz to 20kHz) into equal sections of narrow frequency bands, which can be individually adjusted for gain. Each frequency center rate (CENTER FREGUENCY) differs by 1/3 octave. In electroacoustics, the frequency interval with a center frequency of 2: 1 is called octave. 1/3 octave is to insert two center frequencies between the frequencies of one octave, so that the four frequencies are sequentially different by 1/3 octave. At this time, the ratio of the four frequencies is 1: 1.26: 1.578: 2 and relationship. Professional equalizers are almost all equally divided by 1/3 octave. In short, the more points, the narrower the bandwidth, the larger the Q value. Each frequency is controlled by a push potentiometer, and the position of the potentiometer key can show an intuitive equalization frequency curve (ERECT EQUALISER), so the equalizer is named.
The equalizer can cover the frequency range of 10 octave bands, and its center frequency can be symmetrically peak-valley boosted and attenuated. The maximum level value is ± 15dB, regardless of the boost and cutoff level, its Q value is constant Yes, the filter has a steepness of the same shape. The equalizer is suitable for frequency equalization of ready-made musical works.
Parametric equalizer (PARAMETRIC EQUALISER) has two types, fully parametric and quasi-parametric (FULL? AND and QUASI? PARAMETER), the difference between these two types is: full parametric has three completely non-interacting control adjustment parameters, That is, the peak unit (PEAK BOOST) or valley attenuation (SLAP FADE) in dB units, frequency (frequency most affected by equalization) and adjustable Q value. The above three parameters can be adjusted arbitrarily without mutual influence. When the quasi-parametric equalizer is adjusted and / or balanced, the Q value will change and affect the two frequencies of the center frequency, that is, the bandwidth changes. Visually compare the difference between the complete parametric and quasi-parametric equalization. That is, when doing the in-depth processing of infinite depth (FAT), the fully parametric equalizer can well eliminate harmful sounds in a certain frequency band, and the quasi-parametric equalizer is restricted due to reciprocity and is not suitable for eliminating fixed Interference noise at frequency.
In general, the parametric equalizer is a powerful tool for sound quality processing in applications. It can be used for pre-recording and post-secondary processing. Its function is different from the graphic equalizer. Well-designed parametric equalization can correct the peak frequency response according to acoustic resonance. , Single-frequency equalization of a certain sound or the tone of a certain instrument (TONE COLOR) to a large degree of modification or attenuation of single-frequency interference noise, so the role of improving the sound effect is significant.
The professional parameter equalizer has more obvious advantages in performance and indicators. Such as a certain analog digital control model, programmable stereo dual tracking, there are 8 storage groups, can send and store (RAM) 64 data, which provides convenience for complex and complex equalization processing. And can be connected to the computer through the serial bus. For recording resonance points, displaying input and output gains, reducing and boosting levels, and selected Q values, etc. are all displayed by electronic digital, and input gain and output gain adjustment can be selected within 250 gears. Regardless of the adjustment of the center frequency, Q value, and gain can be adjusted by keys, and have "acceleration control" function (the longer the key is pressed, the faster the changes of various parameters). It can be connected with a computer, because the computer keyboard controls the entire function and monitors data from the screen. And the LOCK button can lock all the control keys on the panel, and the password must be entered through the keyboard to release the LOCK function.
Some full-parameter equalizers have very high performance indicators, such as: the maximum increase can reach 18dB; the maximum reduction can reach 25dB; the frequency bandwidth can be adjusted arbitrarily from 1/12 to 5 octave; the upper limit of the center frequency can reach 30KHz. And it has been developed to fully digital processing, which has a positive effect on supporting digital recording.
The connotation of EQ
Since adjusting the loudness of certain frequencies can achieve the purpose of frequency equalization, can the adjustment of EQ be understood as simply adjusting the high and low frequencies? In fact, the content of EQ is not as simple as we think "add a little high bass or add a little bass".
Before talking about this issue, I will briefly introduce a few concepts. The vocalization of any object is inseparable from vibration. The unit of the number of vibrations of a vocalized object per second is Hz, and the periodic phenomenon within this unit is frequency. The fundamental frequency of the vibration frequency (or fundamental wave) determines the pitch. The frequency is a sine that is an integer multiple of the fundamental frequency, and the oscillation is a harmonic. The frequency is a sine that is twice the fundamental frequency, and the oscillation is the second harmonic. Musicians call the second harmonic per overtone, which is octave higher than the fundamental frequency. The third harmonic frequency is three times the fundamental frequency, also known as the second overtone. Harmonics determine the waveform and make the sound of various musical sounds different. Even on the same tone, due to the different number of harmonics and the strength and weakness of the relationship, different sounds are formed. In other words, the timbre is determined by the relationship and characteristics of the vibration frequencies of the object. These timbre-related characteristics include harmonics, formants, and time transition characteristics, and the key to determining the main timbre of an instrument is the intensity of the first few harmonics.
The strongest harmonic is the center resonance frequency, which is also the formant frequency.
Each lower-order harmonic, when its loudness is higher than other harmonics, will produce its own characteristic influence, so that the timbre changes. The simplest classification is: the lower order harmonics are divided into two groups, odd harmonics (first, third, fifth, etc.) and even harmonics (second, fourth, sixth, etc.). In terms of music, the second harmonic (one octave) is an octave higher than the fundamental wave, which can increase the intensity of the sound and make it more full. The sound of the third harmonic is "dull", but a strong third harmonic can make the tone softer. The fourth and sixth harmonics produce a "chorus" sound. The strong third harmonic plus the fifth harmonic will give the sound a "metallic" texture. When the amplitude of this sound increases, an unpleasant tone is produced. The combination of a strong second harmonic and a strong third harmonic will break the "dull" effect. If the 4th and 5th harmonics are added, the tone becomes open. Those higher harmonics above the seventh harmonic will produce a sharp sound. If there are too many harmonic components that are not related to music, such as the 7th, 9th, and 10th, there will be harsh, unconsonant audio. As far as music is concerned, the more non-consonant sounds in the partial wave, or the intensity of the non-concord partial wave is greater than the consonant partial wave, the sound must be unpleasant. Since the human hearing is very sensitive to these sounds that are side harmonics, control them The amplitude is extremely important. However, the increase in the amplitude of side harmonics (referring to harmonics above the sixth harmonic) or decrease is almost proportional to the loudness. For the human ear, the balance of side harmonics is an extremely important loudness signal.
So, in the pan-music series, what is the internal relationship between human hearing and harmonic order in terms of music?
In terms of music, the relationship between fundamental and harmonics is consistent with the harmonic sequence. The musical sounds are all compound sounds, and the characteristics of the sound spectrum are completely consistent with the degree of harmony of the music schedule. For a brief explanation, please refer to the table below.
Correspondence between human hearing and interval, frequency and harmonics
Harmonic Interval Frequency Ratio Harmonic Order Full Harmony Pure 1/11 (fundamental)
Pure Octave 2/12, 4, 8, 16
Pure fifth degree 3/23, 6, 12, 24
Pure four degrees
Semi-harmonic third degree 5/45, 10, 20
Small third degree
Big Six Degree
Primary Six Degree 8/525
Disharmony Major Degree 9/89, 8
Second degree 17/1617
Big seventh 15/815
Seven degrees 7/47, 14
Four degrees increase 11/811, 22, 33
Through this table, we can find the frequency that is harmonious or discordant with it according to any fundamental frequency. As long as we can know the frequency value of any first harmonic by simple integer multiple multiplication, it is convenient to adjust the EQ instead of blindly starting. . However, the pattern of each harmonic combination must also reflect the relative intensity spectrum state. In other words, we must understand the corresponding relationship between timbre and frequency spectrum. Only by grasping this rule can we be truly targeted. In the following, we will introduce the corresponding relationship between the chromatographic states of several types of sounds with the spectrum of stable sound.
From the spectrum state of the graph, the following subjective timbre hearing can be obtained:
1. There are not many harmonics and the fundamental frequency is strong. If it is located in the low frequency band or the middle frequency band, the listening feeling is as soft as velvet and has a certain sense of warmth.
2. There are not many harmonics and the fundamental frequency is strong. If it is located in a high frequency band, the sound of the sound will be sharp and crisp.
3. There are not many harmonics and each harmonic is strong. The sense of hearing is thin and slender, and there is a certain sense of desolation.
4. There are not too many harmonics, the low-frequency harmonics are stronger, and the less important harmonics are reduced in power and weakened, and the sense of hearing is round and warm.
5. There are many harmonics, but each harmonic is very weak, the sense of hearing is insufficient, and there is a sense of blandness.
6. There are many harmonics, and the lower harmonics are stronger. The harmonics of each order are arranged in descending power. The sense of hearing is full and bright, and full of vitality.
7. Lack of harmonics in the middle frequency band, the harmonics at the low and high ends are strong, and the sense of hearing is empty or has a sense of Xiao Ran.
8. There are many harmonics, but the higher harmonics are prominent, the sound is sharp and harsh, and the sense of hearing is not harmonious.
9. Odd harmonics are strong, even harmonics are weak, the sound is stiff, and the timbre is erratic.
10. Even harmonics are strong, odd harmonics are weak, the sound color has a sense of transparency, and the timbre has a pure color.
From the above example, we can understand that the tone adjustment should be consistent with the physical nature of the sound. Any different combination of frequencies will produce completely different effects. Only by mastering the laws of the spectrum and understanding the acoustic results of various spectrum states can we really Make EQ adjustments to the timbre of the sound.
Adjustment of the best frequency point
From a statistical point of view, the sound emitted by each sounding body has a certain frequency band (frequency range)
Only by regularly grasping the frequency range of the sound source can the targeted sound be balanced and solve the problems encountered in speech practice. If we do not know the basic range of the speech, it is as if the artist does not know the color, and it is impossible to adjust the tone of the speech, but are all the frequencies included in the frequency range of various sound sources useful for equalization? Music, vocals, and sound effects contain a wide range of frequencies, covering almost the entire range that the human ear can perceive. When using an equalizer, it is impossible for us to raise or attenuate all the frequencies contained in a voice or a piece of music. If we do so, we will increase and decrease the volume, and will not play a role in equalizing the frequency.
So how to adjust the frequency spectrum? What frequency can be increased and what frequency should be attenuated? Here we only discuss the problem of adjusting the timbre with you.
As we have said before, when each lower harmonic loudness is higher than other harmonics, it will produce its own characteristic influence and change the timbre. But the harmonics we want to adjust must observe the relative intensity of the tone reference line. In the specific control, the sound of a certain voice is real and true, which shows that the components of the lower harmonics, especially the second harmonic, are stronger. If you adjust the timbre again, you can balance the proportion of each harmonic according to your needs. If you want to make the sound thicker and more powerful, you can increase the 4th, 5th, and 6th harmonics; if you want to make the sound brighter, you can The 10th harmonic increases a bit, and the above frequencies will attenuate the level as the frequency increases. As long as it basically conforms to the timbre reference line, the depth attenuation of the harmonics above the 10th order will work. Another example: the sound of a certain instrument is fictitious and unreal, which shows that the components of the first and second harmonics are weak and the amplitude is small. At this time, the tone adjustment should compensate for the gain of the first and second harmonics. If the sound is still sharp, it means that the amplitude of the treble band is too large or even exceeds the timbre reference line. Therefore, the attenuation of other frequencies should be considered. It is never advisable to increase the chance of distortion.
In the operation of using EQ in COOL EDIT, we can immediately determine what frequency should be adjusted according to the analysis of the timbre. In fact, they first consider the characterization of the main resonance center frequency of the sound source timbre, and then modify it. Some minor harmonics are used to achieve frequency equalization. This includes correct evaluation of timbre and mastery of frequency characteristics. Here are some experiences for everyone.
(1) Listen to determine your evaluation of the sound. Of course, we must understand the correct timbre of the sound source, otherwise we will not aim.
(2) Decide which frequency to adjust according to the subjective evaluation of hearing, that is, determine the rough frequency adjustment range.
(3) Turn the equalized gain to the maximum value to make it convenient for listening.
(4) Use this frequency and nearby frequencies to try to gradually narrow the frequency range. When it is confirmed that the tone of a certain frequency point meets the intent of adjustment, that frequency or a frequency is determined.
(5) Reduce the frequency gain of this segment, and determine the loudness when the hearing frequency balance ratio is appropriate.
(6) Listen carefully again to confirm whether other frequency bands still need to be adjusted until satisfied.
Of course, this method is also suitable for attenuating a certain frequency, and the gain knob is set to a large attenuation value. When scanning this frequency, which frequency is effective for the amount of sound to be reduced, the best attenuation frequency point is found.
Since speech (which should include all sounds) is a composite timbre, and contains many features that need to be portrayed, according to Fourier analysis. In this way, when we are equalizing, we can generally consider the characteristics of the timbre and reflect the whole picture as much as possible according to the relationship between the fundamental wave and the harmonics. Therefore, when performing frequency equalization of a certain segment of speech, it cannot be effective by increasing or decreasing the single-point frequency. In other words, it needs to be processed separately at each frequency. Only by fully exerting the coordination of each frequency of the entire audio range can the voice of this segment reach its own requirements.
In the frequency domain of music programs, each frequency band has its own independent role. The increase or attenuation of each frequency segment will change the content of the musical tone. Below we divide the full audio into six segments for specific analysis:
(1) The frequency range of 16 ~ 80HZ (super bass) can bring a strong feeling to music, especially at frequencies below 20Hz, it can enhance the sense of air vibration, and too much improvement will make the sound turbid. But in the process of replaying our speech, this frequency is generally not replayable.
(2) The frequency range of 80 to 250 Hz (bass) contains the basic sounds of each part in the voice. Adjustment of this frequency can change the balance of the music, making it tend to be full or thin, too much increase will cause "Rumble" (low-frequency buzz RUMBLE). In order to enhance the fullness of the performance of some instruments with weaker sound power, in the processing of vocals, the frequency of the bass can usually be reduced to below 100Hz, but when the frequency below 100Hz is cut off, the low-frequency noise can be eliminated to make the tone more sound. Pure. When the frequency of 100-160Hz is high, the human voice will be low and dull.
(3) The frequency range of 250HZ? 2KHZ (midrange) contains the lower harmonics of most parts, and 250-500Hz affects the strength and firmness of the timbre. 330HZ gives a solid sense of human voice, making the bass soft and full. But too much improvement will produce a "buzzing" bathroom effect. More than 500 to 800 will make the sound stiff. If a wide boost peak is added in the range of 800Hz to 2KHz, the sound will be more prominent. The center frequency gain should generally not exceed 8dB. When the frequency is too high at 500Hz, the sound quality of the cone sound will be generated. When it is used, it is mostly used for the attenuation state. The tone of the phone.
(4) 2K ~ 4KHz (medium-high pitch) frequency band, this frequency should be used with caution, too much increase will mask the recognition of language, especially the lip sounds like "M, B" are easy to blur. We should pay attention to this point. Excessive improvement around 3Khz will cause listening fatigue and upset. The tone of this frequency is flat and sharp, and it has a broken effect on the sense of hierarchy in the middle and high frequencies. It should be used with caution.
(5) The frequency range from 4K to 6KHz (treble) is a frequency band with a sense of presence. It can increase the clarity of language and music. Increasing this frequency can make the distance between the performer and the listener closer. 4Kz has a frequency of penetrating hearing, and 5kHz boost or attenuation has a great influence on the loudness.
(6) The frequency of 6K ~ 16KHz (super treble), this frequency controls the clarity of the brightness of the overall sound. For language programs, raising this frequency too much will accentuate the tooth sound and break the sound. But in the 11025Hz sampling, this frequency is gone. In the application of the frequency of 6.8kHz, attention should be paid to limit the use, because this frequency can cause the resonance of the outer ear of the person, the screaming of the hearing, too much component can destroy the overall sound quality.
We can see from the effect of the above frequency bands that the increase or attenuation of any section of frequency is pros and cons, and the key lies in rational use.
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