Be careful when operating these audio equipment!

There are many kinds of sound equipment. For our sound engineers, we need to adjust every sound equipment properly. We say that the human operation failures mainly occur during the performance, such as silence, disconnection, feedback, noise, etc. Let's talk about the common sound equipment prone to human operation failures one by one:

1、 Mixer

We generally compare the mixing table to the heart or brain of a sound system, so the mixing table is also the sound equipment with the most human operation faults. The human operation faults of the mixing table are generally manifested as: silent, very small, distorted, loud or small, strict back transmission, obvious noise, etc.

1. Channel level attenuation switch of mixer

Some consoles add a level attenuation switch of about 20dB in front of the gain knob. When CD and other sound sources are input from the high resistance port, it may be necessary to press the switch to reduce the sound source signal by 20dB due to the high level. However, if some sound engineers accidentally press the switch during the performance, it is: the boss is angry, and the consequence is serious ! At this time, the sound signal is suddenly increased by 20dB without attenuation. The consequences can be imagined. The light audience will jump up from the chair in fright, and the heavy audience will be reimbursed on the spot. Therefore, we should have clear and definite purpose when adjusting each knob or switch, and do not operate blindly.

2. Gain adjustment of mixer

Some sound engineers don't know the importance of channel gain. They adjust the knob randomly. Sometimes they turn off the gain knob and even press the 20dB level attenuation switch at the same time. How small is the sound at this time? We can't talk about the signal-to-noise ratio and dynamic of music at all. If we adjust the way of thinking about the microphone channel, the singer will only admit that he is unlucky. Even if he shouts sky breaking, he won't have a high and penetrating voice.

Of course, some sound engineers like to adjust the gain to a large value. It's OK for music. At most, the music is hard, but the singer is miserable. A little loud sound is like a flood breaking through a dam, which seems uncontrollable. The high voice will become as noisy as a broken Gong or a exploded bean, because the signal with too large level is seriously distorted. In addition, in this case, the microphone also Will often lose back. It can be seen that the importance of gain will cause accidents during the performance.

3. Adjustment of balance group of mixer

As the name suggests, the tuning table is mainly used to adjust the timbre, and the timbre adjustment mainly depends on the balance group. It's very simple. It's nothing more than the high and low bass plus several corresponding frequency selection knobs. Although the timbre may not be very good under normal operation, there will be no performance accident, but some sound engineers sometimes boldly turn the balance knob around. I see such a sound The loudspeakers will be shocked. If the bass is added to a large scale, the burden of the whole amplifier and speaker will increase greatly, which may damage the equipment, and at the same time, the sound will be easily distorted. If the midrange and treble are added to a large scale, the treble will be dangerous. In a word, it is necessary to raise the balance knob to a certain degree, and excessive promotion will cause unexpected failure.

4. Adjustment of balance group of mixer

As you know, aux is mainly used to send signals to the effector. In a mixer, if we send signals to the effector from aux 6, if we output two signals to 23-24 channels of the mixer after processing by the effector, then the aux 6 knob in the two channels of 23-24 will not be turned on again, otherwise the signals just processed by the effector will flow back to the effector. As a result, there will be another cycle between aux and the effector. When the loop level gain exceeds a certain range, acoustic feedback will occur.

5. Sound and image of mixer

You want to take the audio-visual knob as a dispensable thing. Sometimes when we only output the volume on the left or right of the total output, we need to pay attention to the audio-visual knob. If we use the total output signal on the right and all the audio-visual signals on the channel of the mixing console are on the left, then there will be a silent fault, which is the opposite.

6. Monitor and mute switch of mixer

Generally, the monitor and mute switch of the mixing console are close together. You must see clearly when you operate them. When you press the monitor switch, you will press the mute switch by mistake, which will cause the silent fault.

7. Marshalling problem of mixing table

Of course, it is convenient to control the channel sound by grouping, but since the group buttons are relatively small and many, they must be operated carefully. Once I finished a project acceptance and handed it over to the sound engineer in the ballroom. I put all instruments into 1-2 formation and singer microphones into 3-4 formation. But at this time, a female singer's microphone has a very small sound, only the hollow effect sound is not direct sound. I ran to the mixing console and saw that the female singer's microphone was put into 1-2 formation, so I quickly put the female singer's channel into 3-4 formation Press down, and at the same time press up the 1-2 formation to remove the fault.

There are also some high-quality mixers with group mute function. For example, if we want to set channel 1-10 of the mixers to group mute 1, when we press the main button of group mute 1, channel 1-10 will be muted. Therefore, it must be clearly seen when the group mute operation is performed on the mixer with this function.

8. The ins plug-in and out socket of the mixer

Some sound engineers don't know how to use this socket. If you accidentally insert ins of the mixer into the socket and insert a signal line of TS connector, the total output of the mixer will be silent. This introduction has also been mentioned in my previous articles.

9. Find the interference source of the mixer

Sometimes there will be interference noise in the mixer. When all the branch channel switches are turned off and only the total volume of the mixer is turned on, there will be a lot of noise going out. At this time, we can put on earphones and monitor all the way to see which way the noise comes in, or pull out the input line or even output line of the mixer all the way, and then the noise disappears, We'll find the source of the noise. How to deal with interference sound will be discussed in the following article.

10. Phantom power supply of mixer

Most of the mixer will have a 48 volt phantom power supply, which can be used to push a variety of condenser microphones, but because it is the current transmitted from the microphone line, it is necessary to check the microphone line frequently to ensure that the line is unblocked, otherwise the line will produce a large electric shock sound when the line contact is not good.

There is also a phenomenon: if you use a conference condenser microphone with battery in a mixer, do not turn on the phantom power, otherwise the two may interfere with each other, and may make a "rustling" sound like rain.

2、 Equalizer

Equalizer is the most frequently used equipment in peripheral equipment, so we should pay special attention to it. Here are some problems and troubleshooting to be paid attention to when adjusting equalizer:

1. Some mixing consoles will be equipped with 7-9 section equalizer. Such equalizer can only simply adjust the lower timbre, which belongs to an auxiliary property. Therefore, it is better not to greatly improve such equalizer when we use it, otherwise the main output level of the mixing consoles will often exceed the standard. Another such equalizer generally has a switch. Pay attention to the working state of the switch when using it.

2. Some 15 segment Equalizers with two channels will have a state transition switch, which can convert 15 segment Equalizers with two channels into 30 segment Equalizers with one channel. At this time, it is necessary to see clearly the frequency of each segment before adjusting.

3. We currently use the most dual channel 31 segment equalizer. We need to pay attention to the following points:

a. 6dB and 12dB change-over switch: some equalizers have 6dB and 12dB working state change-over switch, which is better adjusted to 12dB in general.

b. Low pass or high pass: some equalizers have low pass or high pass adjustment functions. When adjusting, you should pay attention to that if you attenuate too much sound in the bass, it will not be full or thin; if you attenuate too much sound in the treble, it will be too dim and have no penetration.

c. Frequency push-pull key: when adjusting, pay attention to each frequency push-pull key of the equalizer to see whether it is normal; at the same time, pay attention to that the push-pull key should not make too much attenuation or promotion, especially when lifting, it should not exceed 6 dB generally.

d. Connection: the input and output of the equalizer generally have two ports, XLR XLR and TRS. In addition to different shapes, the functions are the same. In fact, they are all balanced line ports. Therefore, when we connect the equalizer, we need to use XLR XLR signal line and trs6.35 stereo signal line for balanced connection.

3. Equalizer failure example

a. Once I saw his outdoor performance at a friend's place. Their equipment was very old. Several push-pull keys of the equalizer were lost. I always felt that one of the speakers was in a funk during the performance. I looked carefully at the 630hz push-pull key on the left channel of the equalizer and it was broken. There was only a little bit left in it, but it was still high. That is to say, the frequency of 630hz was raised It's up 12 dB. It's strange that the sound is not so loud. I quickly asked my friend to use a small screwdriver to set the push-pull key of this frequency to the normal position, and the fault was eliminated.

b. Once, they helped an organization to repair a set of stereo. They said that there was no sound in one channel. I saw that other equipment was basically OK. In this system, the XLR XLR and TRS output ports of the equalizer were connected with signal lines. Later, it was found that the inner side of the right channel TRS stereo signal line plug was short circuited, which also caused the XLR XLR XLR port of the right channel to be short circuited, because the inner side of the equalizer was short circuited The XLR port of the unit is connected to the TRS port line. After replacing the trs6.35 stereo plug, the fault is eliminated.

3、 Pressure limiter

The main function of the pressure limiter is, of course, the protection equipment. Here are some problems and troubleshooting that need to be paid attention to when adjusting the pressure limiter:

1. Threshol in noise gate

The noise gate in the pressure limiter doesn't really remove the noise in the music. It only works when there is no useful audio signal in the system. For example, when the leader whispers in the meeting, such useless sound can be intercepted by the noise gate. But when the leader speaks loudly to the microphone, the noise gate can't be intercepted, otherwise there is no sound How can it work when the voice goes out?

The real situation is: when the useful audio signal in the system rushes through the threshold level of the noise gate, actually this threshold level has no effect. At this time, the noise in the system will be mixed with the useful audio signal and transmitted together, but at that time, the noise is covered by the useful audio signal, we can't hear it.

Therefore, the noise gate is actually unable to eliminate any noise in the normal audio signal, it is not like the noise sampler in the audio workstation that can moderately eliminate some noise in the normal audio. If the noise gate is adjusted too high, the phenomenon of "panting" will appear. It will not happen once and for all. It is intermittent. Therefore, this kind of artificial fault should be avoided as far as possible.

2. Threshold in compressor

Although the threshold in the compressor part and the threshold in the noise gate part are both threshold circuits, their functions and working states are quite different. In normal use, the threshold of the noise gate may not work in 99% of the time, because most of the audio level signals will be higher than this threshold; and the threshold of the compressor may also be higher It doesn't work for 70-90% of the time, on the contrary, because most audio level signals may be below this threshold.

3. Compression ratio Ratio ratio

The adjustment of compression ratio actually determines whether the pressure limiter becomes a "compressor" or a "limiter". Its adjustment should be carried out in combination with the threshold of the compressor part. Too low compression ratio does not work, and too high compression ratio sometimes damages the sound quality. Basically, the compression ratio less than 1:6 is the compression function, and the compression ratio greater than 1:6 is the limiting function. Of course, I personally think it's more appropriate to adjust the compression ratio to about 1:3.

4. Stereo interlock

There is a stereo link in the pressure limiter. When you adjust it, you should be careful not to press this key carelessly, which will turn the stereo signal into a mono signal.

5. Pass through: I often find that some sound engineers have passed through the pressure limiter without knowing what is the pass through state and what is the working state, so we should pay attention to this point.

6. Fault Example of pressure limiter

a. Once a set of audio equipment was overhauled, and it was found that one of the pressure limiters was not working properly. Three or four compression indicators were on on one side, and seven or eight compression indicators were on the other side. However, all the equipment in front of the pressure limiter were working normally, so it was only the pressure limiter itself. Later, it was found that the level change-over switch on one side of the back panel of the voltage limiter was placed at - 20. Under normal circumstances, it should be selected to work at + 4dB level. Otherwise, when the level of the voltage limiter does not match the level of other equipment, the signal of the voltage limiter will be easily seriously distorted. We must pay attention to avoid this kind of failure when using.

b. Once my friend asked me to tell him that there was a problem with the sound equipment. During the performance, the music system for playing songs and accompaniment was still normal. However, when the singer suddenly started to sing loudly, the overall volume of the system would suddenly be much smaller, like being out of breath. After a period of time, it gradually returned to normal. I found that they used the 266 pressure limiter of DBX in the United States, as mentioned earlier In fact, the threshold level of the voltage limiter is too low, and the voltage limiter is overloaded. At this time, it is necessary to increase the threshold level, and the fault is eliminated. This phenomenon is also a feature of the 266 voltage limiter of DBX, so we should pay attention to it later.

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