Mixer, multi-channel input signal for amplification, mixing, distribution, sound quality modification and sound effects processing. It is the heart of an audio system, and how this heart's blood circulation directly affects the stability of the entire system.
1 signal input
The input signal of the mixer is roughly divided into two types: low-resistance microphone signal input and high-resistance line signal input. Each input can be thought of as a water pipe, that is, if a mixer has multiple signals input, it seems that there are multiple water pipes flowing into the mixer for processing. The distinction between low resistance and high resistance can be seen as the difference between water pressure or flow speed. For example, the high-impedance input level is high, as if the water pressure is very high, the water flow is more urgent, and it is suitable to input directly into the pool of the mixer. It is not necessary to add any link in the middle to adjust the water pressure and water flow rate; The low-impedance input level is low, as if the water pressure is very low, the water flow is very slow, and it is not suitable to directly input it into the pool of the mixer. It is necessary to add a pump in the large pool to give the low-pressure low water pressure. It is enlarged to speed up the flow of water, so a special circuit amplifier is built into the low-impedance input channel of the mixer to amplify the low level to the appropriate level. The characteristics of water use to describe low-resistance signals and high-resistance signals should be well understood.
2-channel gain adjustment
To input to the sound source in the mixer, first distinguish whether it is low impedance or high impedance, and then connect it to the mixer with the standard signal cable. If you want to achieve perfect sound quality for each source, you need to make careful adjustments. The gain of each input channel of the mixer is very important, but many sound engineers seem to simply see the gain as a volume knob, which is a big mistake. In fact, the gain is mainly used to control the dynamic range of the input signal. When the general gain is adjusted to the maximum without distortion, it is the maximum effective dynamic range, and it is also the best effect state. This is hard to understand. It is also described by water: the input channel and input line of the mixer will have a basic noise floor. The noise floor is like the sediment in the river bottom, which cannot be eliminated. As we all know, when the river is not deep, the flowing water is under the mud, and the water quality is definitely not good. So if the dynamic range of the gain adjustment is not enough, the sound source signal is like the flowing water under the mud, the noise floor will emerge, and the sound quality is definitely not good at this time; when the river is deep, The flowing water is relatively clear, and the water quality is definitely good. That is to say, the dynamic range of the gain adjustment is large and reasonable, so the sound quality is definitely good. Of course, if the water is huge, even the river dam will be washed, and the river bottom will give Overturned, this is equivalent to the level signal is too large, this time can not talk about the sound quality, but also damage to the equipment, so the gain is not the bigger the better, to have a degree, suitable. The author wants to describe the effect of gains, even if it is a beginner of audio, it should be understood.
3-channel equalization group adjustment
When the gain is adjusted, it is generally necessary to adjust the equalization group of the mixer channel. The adjustment sequence should be first adjusted from the bass part and then adjusted to the high-pitched part. Because only the fundamental sound of the sound is guaranteed, the sound can be guaranteed to have multiple overtones. The basic adjustment is no problem for everyone. Here I only talk about a few technical aspects.
Now the balance group of professional mixers usually has frequency selection adjustment. Many sound engineers will not use them flexibly. It is difficult to say all the details. Some things depend on personal understanding. The author can only talk about simple things: It is said that when playing the disco music, the bass is not strong enough. You can choose the bass frequency of the channel equalization group of the disco music to be around 200Hz, and then use the adjustment knob to moderately increase, so that the bass strength comes out; When a female singer's tooth sound is obviously prominent, the high-frequency frequency can be selected at about 6000 Hz, and then the adjustment knob is used for moderate attenuation, so that the tooth tone is appropriately reduced. If the application is flexible, you can also use the equalization group's frequency selection function to suppress the acoustic feedback. For example, there will be a formant around 300Hz in the general ballroom. Usually this frequency is easy to produce acoustic feedback. You can select the frequency of the microphone input channel at around 300Hz. Then use the adjustment knob for moderate attenuation, which can effectively reduce the acoustic feedback. Of course, the frequency of acoustic feedback generated by each sound field is different, but no matter what frequency the acoustic feedback can be controlled by this method, of course, this needs to be flexibly controlled according to experience, and the sound field should be perfectly adjusted and avoided. Acoustic feedback needs to be adjusted with a professional multi-band equalizer or feedback suppressor.
In short, a mixer, the need for the sound engineer to constantly adjust is the balance group of the mixer. I often see that some sound engineers only know the push-pull volume fader, too lazy or do not know how to adjust the equalization knob. In fact, in use, it can be said that the mixer needs to be adjusted every moment.
Take a song as an example: When the singer goes to the stage to introduce his own performance, you need to turn off the bass of the microphone, adjust the reverb to moderate or turn off, so that the clarity of the language can be guaranteed; when the music sings the singer When you start singing, you need to increase the bass of the microphone, otherwise the sound will be thin and the reverberation volume will be increased. In addition, in order to avoid the high-pitched sound of the microphone, you can attenuate the music treble; but when the song is between When playing, the audience's attention will be transferred from the singer to the music, so at this time you need to increase the treble of the music, and at the same time open the music sound, so that the music will be very good and natural, otherwise No change will be too rigid. And at this time, the reverberation volume should be turned down, so that even if the singer suddenly speaks during the interlude, there will be no complicated reverberation; when the song is finished, the next concert will be closed. , attenuate music treble, push up the microphone and reverb volume. At the climax of the final singer, you need to turn the mic volume up, then turn the volume of the music from small to large, creating a perfect, shocking, magnificent orgasm effect to end, of course not all songs are suitable for this. The operation, so what the sound engineer needs is flexible.
4-channel AUX adjustment
The various adjustment knobs on the mixer are generally the most in the equalization group. The next step is the AUX knob. The term is called: Aux Send Control. Because it is an auxiliary nature, so many sound engineers pay less attention to it, and do not fully understand its function. I remember that when I was studying in the Beijing Radio and Television Department in 1997, I talked about this AUX teacher for two days, but many students were still confused. In the end, the author couldn't help it. It took two minutes to solve the confusion of them for two days. After I understood that many of my classmates were sighing that this AUX was so simple! Of course, I can't say that the author was at a higher level. Teacher, just the author used an image metaphor: The author said that each input channel of the mixer is like a large water pipe. After the water comes in, it is basically divided into two main water pipes, A and B. The water pipe is: the volume fader of the channel of the mixer, sent out by grouping, etc., everyone knows the channel volume fader; the other B road water pipe is: AUX group, the difference is a mixer The AUX part can be divided into multiple channels. If a mixer has 4 channels of AUX, it seems that the AUX group is divided into 4 small pipes and then flowed out. It is the same as the principle of the fader below, except that most AUX volume switches are controlled by knobs, and the channel volume switch of one channel is controlled by a fader, just like a large water pipe even if it is divided into A , B two main water pipes, and they are divided into a lot of small water pipes, but the water quality is still the same. So you can't just look at the surface differences of things. In fact, their functions are similar. Most of the audio beginners should be able to understand this. The most important thing is that the AUX knob can be used in the same way as the mixer's volume fader function.
Next, we will talk about the specific use of the AUX group: Generally, AUX is used for external vocal effects. The sound that needs to be processed is sent to the effect processor with the corresponding AUX switch, and then flows back to the effect processor. Tuning, this is the basic knowledge, most sound engineers should be. The AUX of a large console generally has a pre/post fader. When set in front of the fader, the total volume fader below the channel has no way to control the volume of the AUX; instead, it is subject to this channel. Volume control. Other features of AUX are for listening or recording. Another convenient use is that readers can also use AUX to control the bass volume of an audio system, so that more bass channels can be used to open the corresponding AUX without the need for loud and subwoofer sources such as microphones. The corresponding AUX can be opened with less volume, otherwise it will easily produce bass feedback. In general, I understand the principle of AUX can be inferior, I do not say much here.
5 image balance adjustment
The sound of the mixer is generally understood by the sound engineer, but many of them are rigid understandings. For example, a two-channel stereo music signal is input to the mixer, and most sound engineers will turn the sound channels of these two channels toward Left and right to the end, think that this is "stereo", in fact, the sound coming out of these two channels will appear very floating, the middle is imaginary, powerless; if you put the sound image knob in the middle, you will feel the music sound Going up to the head, it's hard to accept, and the width of the sound is not enough; the best position is that the panning knob of the left channel turns to the 9 o'clock position of the clock, and the panning knob of the right channel goes to the 15 o'clock position of the clock. Music will not spread the dynamic range and width, and the strength and penetration are good. Everyone can try it carefully, the author does not analyze the principle, the author only pays attention to practice. The other aspects of the sound image application are not much to say, are the basic knowledge. In fact, it is often considered the simplest thing, and it is very complicated to think about it.
6 main output part adjustment
The main output portion of the mixer refers to the grouping volume and total volume. For example, the band can be programmed into 1-2 groups; the microphones can be programmed into 3-4 groups; the bass can be controlled by the volume of the 5-6 group, and the auxiliary speakers can be controlled by the volume of the 7-8 group, in short, there are multiple Grouped mixers are easier to control. In addition, the group can choose to output the signal separately or cut the grouped signal into the mixer's master volume mixing control. Others such as channel faders are very simple, but the volume fader should be flexibly controlled according to the condition of each input channel. This part of the adjustment is simple but very important, mainly to observe the input and output levels of each signal. Signal, there can be no serious distortion.
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