Application of digital mixing console in integrated video conference system
The video conference system established by public security systems at all levels across the country has played a very important role in the rapid response emergency communication guarantee and the smooth flow of police orders. In view of the fact that this equipment cannot cause problems at critical moments, the Ministry of Public Security has established four video conference systems in the image control center of the provincial (district) office, and at least one system has also been established in the province to the city. Due to the need for more and more venues, such as video and telephone conference rooms, command centers, direct and image control centers, etc., so many conference systems are used at the same time and ensure normal operation, the previous solution is to place a few mixers for Interconnect, and temporarily adjust and plug the required audio signal to a separate mixer when the conference is held at the same time, so as to be independent of each other, so as to achieve the effect of not interfering with each other. However, this method has many disadvantages. Generally, technicians who are not familiar with the mixer cannot control the conference system. At the same time, the socket of the mixer is frequently plugged and unplugged, which makes it easy to make poor contact at the interface, causing hidden technical failures and difficult to troubleshoot. .
In order to solve the above problems, the author used the digital mixer Yamaha LS-9 as the core to integrate the audio signal of the video conference system, and achieved very good results. Generally, technicians who cannot demodulate the performance of the sound console can easily get started with the conference system.
1 Overview of the digital mixer
The digital mixing console is a tuning device with a computer LCD screen. It has multiple inputs and outputs. Each input and output can be displayed by a computer. The digital mixing console also contains digital processors for effectors, reverberators, equalizers, and peripheral devices such as compression, expansion, and limiters. There are a variety of operation menus to call.
Because the digital signal can be easily made very high in terms of total harmonic distortion and equivalent input noise, and the adjustment actions of all its functional units can be easily fully automated. The main features of the digital mixer are as follows.
1) The storability of the operation process. All operation instructions of the digital mixing console can be stored on a magnetic disk, so that the original operation scheme can be reproduced later.
2) Digital processing of signals. The digital signal flowing in the mixer can be used directly for digital effect processing without having to go through digital / analog and analog / digital conversion, which is simple and convenient.
3) The digital mixer has a high signal-to-noise ratio and a large dynamic range. The alternative noise interference source has no effect on the digital signal, so the signal-to-noise ratio and dynamics of the digital mixer can easily be 10 dB better than the analog mixer, and the isolation of each channel can reach 110 dB.
4) The sampling frequency of 44.1 kHz at 20 bit can ensure that the frequency response unevenness in the range of 20 Hz to 20 kHz is less than ± 1 dB.
5) Each channel can be conveniently set with digital compression limiter and noise reduction expander, which can be used to perform necessary technical processing on the audio source.
6) The shift register of the digital channel can give enough signal delay time to adjust the rhythm of each part synchronously.
7) The linkage adjustment of the two channels of stereo is very convenient. Because the channel status adjustment process, all data can be easily copied from one channel to another channel.
8) The digital mixer is equipped with automatic fault diagnosis function.
2 Implementation of the plan
In the image control center of the audio signal collection point, the Yamaha LS-9 digital mixer is used as the control core of the system. The system configuration is shown in Figure 1.
The mixer has 16 ~ 64 input channels, especially up to 16 ~ 32 individually adjustable MIX mixing output channels, and each input and output channel has powerful audio dynamic processing, equivalent to one The digital audio matrix is ​​powerful and easy to use.
At the same time, the mixer also has a USB interface for storing recorders, players, and comprehensive scene storage and callback, as well as any external pre-connected jumper effects and pre-fader auxiliary mixing *. The LS-9's effect device provides 34 different types of effects. The digital mixer uses a linear 20 bit A / DD / A conversion device with a dynamic range of 105 dB and a sampling frequency of 44.1 kHz and 48 kHz. Use LS-9's powerful mixing function and comprehensive scene storage callback to complete the integration of multiple audio signals.
1) Audio signal networking mode
First place two LS-9s in the image control center of the signal collection point, one of which is used to collect audio signals from various venues and the Ministry of Public Security, and the other is used to receive and send audio signals from various cities; Ordinary mixer can be used to exchange audio signals with the center, as shown in Figure 1.
Fig.1 System configuration of image control center
2) Plan the scene in detail
This step is critical. Different venues have detailed and different uses. The venue used in each meeting is different. Therefore, when multiple conferences are held at the same time, there will be multiple combinations of the use of the venue. This requires a good meeting. In the analysis of the specific situation before, list the possible situations, be prepared, and avoid problems and surprises.
What kind of specific scenes are there usually? For example, the video call of the image control center of the central control point of each province is set to A, which is scene 1; use the video and telephone conference room to hold a video conference for each city separately, and set it to B, which is scene 2. When Scene 1 and Scene 2 do not appear in a time period, both are independent scenes and will not have any mutual influence.
When scene 1 and scene 2 need to hold separate meetings in the same time period, the two cannot mix and there will be a conflict, so this requires setting scene 3 on the LS-9, namely A ∪ B, both Proceed but do not interfere with each other. Similarly, when video conferences are held in various provinces, video and telephone conference rooms are used, and each city also needs to participate in the conference. At this time, scene 4 should be set to meet this situation, that is, A ∩ B is set on LS-9. Situation, both video conferences need to be mixed.
By analogy, no matter how many conferences there are and how many conference venues there are, you can plan the scene in advance and set up various parameter storage according to this method.
3) Use comprehensive channel functions and intuitive Selected Channel to set parameters
The LS-9 mixer has powerful channel functions, and their operation is similar to an intuitive and convenient digital audio matrix. In each scene, each audio input signal is sent to the 16 channels of the LS-9. For the definition of the scene, turn the MIX bus knob of the 16 channels of the mixing output channel to the appropriate position, and turn off the MIX bus returning to the local side; at the same time, the definition of the audio input and output lines needs to be consistent, that is, The A signal enters the input 1 of LS-9, and the output 1 of LS-9 also sends the signal to A, so that errors in operation can be avoided.
As in the above scenario 3, it is the situation of A ∪ B, that is, the sound of the Ministry of Public Security cannot be sent to the conference room of the TV and telephone in the hall. The incoming audio signal enters input 3, so that the knob sent to MIX bus 3 (that is, output 3) in input 1 and the MIX bus 1 (that is, output 1) that returns to itself need to be closed; the same is sent to MIX in input 3 Both the bus 1 (ie output 1) and the knob that returns to its own MIX bus 3 (ie output 3) also need to be turned off.
In scene 4, it is the situation of A ∩ B, that is, the sound of the Ministry of Public Security needs to be mixed with the sound of the hall ’s TV and telephone conference room. If the audio signal sent by the Ministry of Public Security enters the input 1 of LS-9, the hall TV The audio signal from the telephone room enters input 3, so that the knob sent to MIX bus 3 (that is, output 3) in input 1 needs to be turned to an appropriate level, and returns to the knob of its own MIX bus 1 (that is, output 1). It needs to be closed; in the same way, the knob sent to MIX bus 1 (that is, output 1) in input 3 needs to be turned to an appropriate level, and the knob that returns to its own MIX bus 3 (that is, output 3) needs to be turned off.
By analogy, the settings of each audio input signal are different in each scene, and need to be completed according to the definition of the scene. After completing these settings, you can define the commonly used scenes on the right of the LS-9 12 numbers Jian Shang. When the conference is held, only one key is needed to call the desired scene, and the rest is to use the faders to adjust the size of each audio input signal appropriately.
4) Other practical functions
(1) Beginners can fully set and monitor channel signals through the LCD display and independent LED level meters. You can also return to the main operating mode with one touch of the "HOME" key.
(2) Use the built-in USB storage recorder / player together with a USB memory stick plugged into the USB interface of the mixer to record MP3 formats at 96 Kb / s, 128 Kb / s, and 192 Kb / s. File and play it back.
(3) The comprehensive scene storage has backup and lock functions. The backup function means that after the LS-9 is set, it can be saved as a file and exported to the storage device for storage; the lock function means that after the scene is locked, other human errors can be avoided Changes in setting parameters caused by operation.
(4) Connect the LS-9 to a common computer via a network cable, and the operator can perform remote control through the computer running management software.
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