Why should we use automatic mixing technology?
Automatic mixing technology is not a new technology. From the 1970s, various types of automatic mixers, as well as various patents, have now become a function in DSP equipment. The shape of the automatic mixer is gradually changing from a stand-alone device to a virtual programming algorithm. Although the software algorithms of various companies will not be announced, we can better understand and use the automatic mixing function in DSP by understanding the core technology and principles in the automatic mixer. A conference room of tens of square meters often needs to plug a dozen or more microphones. Sound engineers will encounter a phenomenon when debugging: one microphone is debugged until it does not howl, but when two or more microphones are turned on, it will whine inexplicably. This is also a law often mentioned by audio people: the number of open microphones is doubled, and the system gain is increased by 3dB, which is NOMG (Number of Open Microphone Gain) = 10lg (NOM). Automatic mixing technology Automatically turn on or off the microphone according to the level, which can automatically balance the system gain that is increased by doubling the number of turned on microphones. In fact, it is very similar to the first method, except that the person becomes a device at this time. The demand for the remaining amount, and the microphone is in the form of a gooseneck microphone, the final sound will be much better than the conference system. But in fact, a single automatic mixer is actually similar to the conference system, and the final mixing is all the way to processing Equipment for processing. This form of processing is actually as problematic as the conference system. Therefore, we generally recommend to customers to use DSP equipment with automatic mixer function. Each microphone can be correspondingly and accurately debugged, so that the sound quality is optimized, and some have direct output function of automatic mixer, which can be easily done. To MIX-MINUS, which is almost impossible to achieve with ordinary automatic mixers or conference systems. And because it can combine the rich functions of DSP itself, it can realize the functions of many conference systems such as chairman priority, request to speak, camera tracking and so on. The automatic mixer needs to have 2 basic elements: 1. When and how to turn the microphone on and off; 2. How to balance the NOM gain. Technically, it can be divided into two categories: Gating and Gainsharing automatic mixers. As the name suggests, the Gating automatic mixer will have a threshold to control the switch of the microphone. If the sound exceeds the threshold, the microphone will be turned on, and if the sound is below the threshold, the microphone will be turned off. How to get the best threshold (Threshold)? Fixed threshold: The simplest and most common is to use a voice trigger switch or noise gate to set a fixed value. Above this value, the microphone is turned on, and below it, it is turned off. Usually this value can be adjusted, but it cannot be adjusted according to the environmental noise, so the effect obtained is often unsatisfactory. In many cases, if the setting is too small, the sound of ambient noise, applause and some music can easily turn on the microphone. If the setting is too high, it is easy to appear to eat words or sound jam. Another problem when using noise gates and other devices is that when the whole applause occurs, all microphones are turned on, and the system and it are prone to howling. Due to the simple implementation of the fixed threshold and low cost, many automatic mixers and software-based automatic mixers still use similar methods to make decisions, and the final results are often poor. Adaptive threshold: Since it is difficult to obtain good results with fixed thresholds, various manufacturers have successively launched their own adaptive threshold circuits or algorithms, which can obtain new thresholds in real time according to environmental noise, and the final effects are different. From an engineer's point of view, we need to understand and know which parameters of the Gating automatic mixer can be controlled to achieve it well! Last On: Last On ensures that even if no voice is detected, the microphone that last spoke will remain on. This function can ensure that the speaker can not turn on the microphone when the level is below the threshold during the sentence break, thus avoiding the problem of the loss of the prefix when speaking next. Mute: The overall output of the automatic mixer is muted. Gain: The overall output level gain of the automatic mixer. Hold: Hold function can adjust the length of time the channel remains open after the speaker stops speaking. This function ensures that the short pause between words and sentences when the speaker is speaking will not cause the channel to close. Off Gain: The level of the off channel. For example, the first microphone is turned on during the speech, and the second microphone is turned on to talk, then the microphone two will gain, but the gain is the value set by the microphone second speech level plus Off Gain. Excessively high settings will cause room noise and reverberation to be received by microphones that are not turned on. A setting value that is too low will prevent the microphone 2 from outputting a sufficient level. Sensitivity: Sensitivity control, the channel must be turned on when it exceeds the adaptive noise threshold of the channel. If the value of this setting is increased, the channel will be easily turned on under very quiet noise. In my experience, a noisy room requires a lower setting value than a quiet room. Because in a quiet room, even very low-level sounds will be much higher than the background noise. NOM Atten: The NOM attenuation fader can affect the amount of attenuation of all channels when more microphones are turned on. This parameter reflects the attenuation when two microphones are turned on, as well as the additional attenuation that will be added after doubling the number of microphones turned on. For example, when it is set to 3dB, the attenuation will be 3dB when two microphones are turned on, 6dB when four microphones are turned on, and 9dB when 8 microphones are turned on. Similarly, doubling the number of microphones will increase the output attenuation by 3dB. NOM Limit: Set the maximum number of microphones turned on. Channels that are not in Auto mode or have been muted are not included. After understanding the meaning of each parameter, it is much simpler to implement. Then the only difficulty is in obtaining the automatic threshold. 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