When using a microphone for live amplification, there will be a problem of microphone squealing (self excited squealing caused by positive feedback of the line signal will not be discussed this time). Simply put, this is when the sound signal is sent out from the speaker and then input into the amplification system again from the microphone, forming a signal superposition, generating positive feedback and causing squealing. Sound workers have been trying various methods and equipment to solve this problem, But it's not very ideal. Based on my own experience, there are several ways that everyone can choose to try:
1. Feedback suppressor: Its working principle is to suppress the level of several or more frequency points that exceed the preset level value in the signal, in order to achieve the purpose of suppressing whistling. This method still has a certain effect on fixed microphone placement and conference amplification, but it is not effective when used in stage performances and may even result in damaging the performance, When performing on stage, actors are constantly moving in different places, making it difficult to track frequency points. Secondly, actors (especially rock singers) are very dynamic during singing, which makes many frequency points' level values not overloaded due to whistling. At this time, the feedback suppressor will mistakenly think that whistling has occurred and suppress these frequency points, causing the sound pressure of the performance to collapse, disrupting the normal performance effect.
2. Frequency shifter: Its working principle is to shift the frequency points of the microphone signal up or down by a few or dozens of frequency points, achieving the goal of not generating positive feedback. This method is also only suitable for use during conference amplification, because the frequency change effect generated by the frequency shifter during performances can be very funny, making it difficult for everyone to find the north.
3. Automatic mixing station: Its working principle is to use an automatic delay noise gate to turn on/off microphones with and without signal input to achieve the purpose of eliminating whistling. This method is very suitable for meeting places with a large number of microphones, and can also be used in language programs during stage performances, but the effect is not good when used in song and dance programs (see noise gate for reasons).
4. Noise gate: Its working principle is to use the threshold level to process the microphone signal on/off, achieving the purpose of eliminating whistling. This method is generally used for drum pickup (drum source pickup method is not included), and only when the drum is hit, the microphone will conduct to prevent signal positive feedback and whistling between the stage return speaker and the drum pickup microphone. However, it is not good for music and dance programs, Because some program actors have a very light voice, at this time, the noise gate cannot reach the threshold level of the noise gate, and the noise gate is not conductive, which can cause on-site "loss of voice".
5. Compressor: Its working principle is that when the signal exceeds the set level value, the compressor starts to compress the signal proportionally to prevent the signal from further expanding and achieve the purpose of eliminating whistling. This method can be used in stage performances of singing and dancing programs, but it is powerless to deal with whistling that did not reach the set level in the early stages.
6. Graphic equalizer: Its working principle is to attenuate or cut off certain frequency points where whistling occurs to prevent whistling. However, its disadvantage is that the frequency point setting is fixed, while the frequency point where whistling occurs is not fixed, which may appear in the first 3/4, 1/2, or last 3/4 of two frequency points... Therefore, sometimes it is necessary to attenuate both adjacent frequency points, and the bandwidth of the graphic equalizer is relatively large, Attenuation or removal of some frequency points can cause frequency collapse and distortion, so the equalizer shown in the diagram is only suitable for situations where there is not a high demand for amplification.
7. Parameter equalizer: Its working principle is to sweep the frequency sweeper to the frequency point where whistling occurs, adjust the bandwidth of that point, and then attenuate or cut off the point to achieve both eliminating whistling and ensuring that useful signals are not attenuated or cut off. Therefore, parameter equalizer is more suitable for various occasions.
The above are some experiences for eliminating whistling, and of course, it should be determined based on the actual situation, including testing. It is recommended not to use dedicated testing microphones for whistling point testing, but to use microphones used on-site for testing, as it is impossible for actors to use the testing microphones for singing. Additionally, methods such as connection also require practice, The usual method I use is to connect a parameter equalizer+compressor to the breakpoint of the microphone input path (one set per microphone), a drum path+noise gate. Of course, this requires a lot of equipment and investment, and everyone can choose to use the equipment and method according to their specific situation (perhaps there is a better method).
