To make the video conference better, we must improve the aesthetic appreciation of the sound and artistic accomplishment, and conceive and creative the restoration of sound in order to improve the artistic expression of sound.
The restoration of sound is an organic combination of technology and art. The quality of the sound must be measured both in subjective and objective terms. With the increase in the degree of informatization of organization work, video conferencing systems in all provinces and cities have been extended to varying degrees. The design, purchase, installation, and commissioning of the entire system have involved audio, video, power, and other factors. This article discusses related technical issues and proposes different solutions.
I. Signal flow The equipment in the conference venue includes the conference terminal and related external equipment. The equipment types and functions are similar. As can be seen from the above figure, the audio signal transmission process is divided into two parts:
1 The voice of the local end is picked up by a microphone, and the vocal voice is converted into an electric signal and sent to the mixer for amplification, mixing, distribution, sound quality modification and effect processing. The signal is then divided into two paths: the one-way signal sent to the local power amplifier. After amplification, it is restored to sound through the speaker; another signal is sent from the console's auxiliary output (AUXOUT) to the conference terminal and transmitted to the remote end.
2 After the signal sent from the remote end is processed by the conference terminal, the audio signal enters the mixer for processing, and is sent to the local power amplifier for amplification, which is restored to the sound by the speaker.
The above analysis shows that the mixer is the convergence point for each signal processing. How to adjust the various knobs and function keys of the mixer is the key to debugging.
Second, there are problems Throughout a variety of large and small video conferences, the quality of sound recovery has been significantly improved, but there are still some problems, mainly as loud noise, distortion, non-standard levels, frequency response is not uniform, Distorted sound ratio, improper reverb delay, etc.
1, noise. It affects the clarity, softness, and brightness of the sound. When it is serious, it can obscure the sound of the venue. 1 Noise floor. The noise floor will appear due to excessive gain, automatic gain control, and impedance mismatch. 2 The microphone "pops". The microphone is the first part of the public address system. The quality of the signal directly influences the effect of the entire meeting. Therefore, according to its characteristics and performance, the characteristics of sound source reproduction, and the relative relationship between sound sources Settings. For speakers who have strong breaks, they should use a microphone that prevents sounds.
2, great distortion. It is related to the nonlinear distortion and human factors of the equipment. It is characterized by hoarseness, breakage, and harshness. When severe, it affects the clarity, softness, brightness, fullness, and presence of the sound. Causes of distortion are many reasons, such as the microphone's high sensitivity, improper placement, power supply microphone is not normal, the mixer's level adjustment is too large, the equalizer adjustment is not appropriate, between the devices Impedance mismatch, etc.
3, the level is not standardized. No adjustments were made to mixers, equalizers, etc. before commissioning, resulting in signal levels that were too high or too low. In addition, the unbalanced line output is directly connected to the balanced line input, causing the signal level to drop.
4, uneven frequency response. It is related to the frequency response indicators and human factors of the equipment. For example, if the microphone is pointing away from the sound source, too much attenuation of the intermediate frequency and low frequency, and the microphone transmission line is too long, it will affect the clarity, layering, and fullness of the sound restoration.
5. The sound is out of proportion. If the ratio of the sound between the main control room, the main site, and the sub-sites to be spoken is out of balance, it will affect the balance of other sub-meetings to restore the remote sound, and the overall effect of the meeting will be reduced.
6, improper reverberation delay. Different types of meetings and pickup environments require different reverberations and delays, so adjust the reverberation and delay parameters based on acoustic characteristics.
1 The size of the venue affects the time of reflection in the reverberation of the sound field and the sense of time in the auditory sense.
2 The reverberation time reflects the process of sound absorption from the sound source through the surrounding absorption and reflection. The reverberation time depends on the size of the venue. The larger the space, the greater the reverberation time. It is necessary to make up for and modify certain sound defects through audio processing equipment, but if it is not adjusted properly, it will be counterproductive. If the reverberation time is too long, the sound will have a "turbidity". Therefore, in combination with reality, a reverberation effect should be added to enhance the sound depth. The same is true for delay processing.
3 The frequency characteristics of reverberation reflect the reverberation effect and sound quality of the sound at different frequencies. To familiarize yourself with the frequency characteristics of reverberation, adjust the ratio of the direct and reflected sound picked up by the microphone to increase the realism and sharpness of the sound.
4 sound diffusion is a parameter that reflects the acoustic properties of the venue. The microphone should be set reasonably to make up for the defects of the sound diffusion conditions of the venue, while avoiding the area with judder echo and the direction of strong reflection.
Third, the interference of common interference audio signals in the transmission process is many, common power interference, interference between devices, light interference and so on.
1, power interference. Poor grounding of the power supply, poor ground contact and impedance mismatch between devices, power supply of the device without "cleaning", audio cable and AC wire laying on the same pipe, on the same ditch, or on the same bridge, will cause noise interference to the audio signal. , forming a low-frequency exchange "click" sound.
2. Interference between devices. "Howling" is caused by positive feedback between the speaker and the microphone. The main reason is that the microphone is too close to the speaker or the microphone is pointing to the speaker. The “space noise†is generated by the sound wave delay, if the microphone picks up the sound source signal and picks up the amplified sound recovery signal, or two microphones with different distance from the sound source pick up the signal of the same sound source, or a microphone picks up The signal of another microphone after being amplified will produce a corresponding path difference and cause a delay. When these signals are superimposed, some of the frequency components cancel each other, forming a "space noise."
Fourth, processing methods Video conference sound recovery, according to the theoretical knowledge of acoustics, according to different actual conditions, flexible adjustment of the mixer and equalizer, the sound processing and beautification, make up for the sound field defects, create a more ideal acoustic environment Properly adjust the compression limiter, encounter sudden large peak signal is not overloaded and distortion, but also to avoid the compression limiter is in a compressed state for a long time, so that the sound convergence smooth and rounded.
For power interference, the following methods can be used to solve: 1 With Sizheng professional power adapter, "clean" interference, output power; 2 signal input and output lines and power lines are separated, and can not be parallel wiring, to avoid adjacent and Cross-interference, mutual induction; 3 using twisted pair power lines, so that the total flux generated by the two wires cancel each other out.
For the "howling" phenomenon, the following methods can be used to avoid the formation of a natural resonance point: 1 reduce the gain of sound reinforcement; 2 use an equalizer or an automatic feedback suppressor to reduce the amplitude of the "howling" frequency point; 3 connect a frequency shifter or adjust Phaser, use the offset frequency or phase to destroy the in-phase condition of the feedback sound and the sound source; 4 adjust the speaker layout, change the microphone direction, and the distance between the two, to avoid the formation of positive feedback.
For the “space noise†phenomenon, the following methods can be used to avoid acoustic delay: 1 Select a microphone with strong directivity; 2 Turn off the ST switch in the mixer or pull down the extra microphone putter; 3 Adjust the sound source and its amplified sound The proportion of restored sound.
In summary, to make the video conference better, we must improve the aesthetic appreciation of sound and artistic accomplishment, and propose solutions to various problems of sound appearance. Guangzhou Sizheng Electronic Technology Co., Ltd., It is the leading audio solution provider in China. As a domestic real audio solution developer, Sizheng is committed to providing users with the most practical solutions and products.
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