Why whistling in monitoring video recording pickup applications
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Near-end howling produces loops
Because of its built-in preamplifier, the pickup has a pickup range that is many times larger than that of a microphone. This is equivalent to an integrated microphone amplifier and microphone, so that the pickup distance is 3 meters, 5 meters or even farther. The D loop is more likely to occur, and it is more likely to produce howling. Relative to the microphone can reduce the sensitivity, the pickup can not, or can not play the sound effect, so the field application process, if the pickup and the local loudspeaker in the same room, the howling sound is very obvious.
Due to the far distance between pickups of pickups, in some cases, they are also used as pickup devices for voice intercom, so there is another kind of howling circuit. This is the worst case of howling during the application of pickups. Specifically, as shown in Figure 2 below, since there is a line echo in B1, there are A1, B1, C1, and D1 howling circuits, and since there is line echo in B3, there are A1, B2, B3, B4, C1, and D1 howling circuits. The coupling of the two whistling loops results in more powerful whistling. In the field, the simplest method is to cut off the loop of D1, but the loop is often difficult to complete, causing problems in the use of pickups.
Two-way call complex whistle loop
For the first two cases, it is also the case that the actual use of pickups (pickup heads, monitor heads) is the most prone to problems. As the microphones, because of the longer development time, the howling research is deeper, and there are generally frequency shifts, phase shifts, equalization, and feedback suppression. The device, but these devices can only be used as a meeting venue, and in the use of the actual pickup due to the price and construction, the difficulty of use, these simply can not be used, here, according to the experience of the senior audio engineer, recommend the following A simple adjustment method.
1. If there is a need for local sound reinforcement, especially for windows, try to make the loudspeakers outside of the window as far away as possible, and use the directional pickups as much as possible for the inside of the window, and make it point to the direction of loudspeaker amplification. On the contrary, and adjust the sensitivity of the pickup, it is not easy to produce howling, and adjust down properly, in general, this kind of way, can make the pickup within 1 meter is not easy to produce howling.
2. Similar to the first type of local sound reinforcement, you can choose to use the capacitive microphone pickup of the pressure sensor, and the distance between the microphone and the microphone is farthest away. If you can, you can use several microphones in order to be able to get a far distance sound. Close-range pickups (eg, less than 50cm) are cascaded and switched for better sound reinforcement. This application has been seen in classroom lecterns.
3. If for the second kind of complex whistle loop, in particular, it is necessary to reduce the howling caused by acoustic echo, on the one hand, a one-way conversation can be set through the software side, or a hardware switching action can be used to select a one-way conversation, and hand-switching. Calling order, to complete the elimination of line echo when the two-way conversation, on the other hand, due to the presence of line echo, but also try to isolate the D1 circuit in Figure 2, the specific way as the first two points are similar.
4. You can choose a microphone with a pressure limiter, which can suppress the opening of the howling to some extent, or add a noise gate control to the output of the pickup. When the unmanned sound is the sound output is turned off, this prevents the screaming. The occurrence of the call.