Sound restoration is an organic combination of technology and art, and its quality should be measured both subjectively and objectively. With the improvement of the informationization of organizational work, the video conferencing systems of various provinces and cities have different degrees of extension. The design, purchase, installation and debugging of the whole system involve the influence of audio, video, power, lighting and other factors. So what are the reasons for the audio interference in the conference system, and what is the processing method?
First, the conference system signal flow
The equipment of the conference venue includes the conference terminal and related external equipment, and the types and functions of the equipment are similar. As can be seen from the above figure, the transmission process of the audio signal is divided into two parts: 1 The sound of the local end is picked up by the microphone, and the voice is converted into an electric signal and sent to the mixer for amplification, mixing, distribution, sound quality modification and effect processing. After that, it is divided into two ways: one signal is sent to the local power amplifier for amplification and then restored to sound by the speaker; the other signal is sent to the conference terminal by the auxiliary output (AUX OUT) of the mixer and transmitted to the far end. 2 After the signal sent from the far end is processed by the conference terminal, the audio signal enters the mixer for processing, and then sent to the power amplifier of the local end for amplification, and is restored to sound through the speaker. The above analysis shows that the mixer is the convergence point of each signal processing. How to adjust the knobs and function keys of the mixer is the key to debugging.
Second, there are problems with audio interference
Throughout the routine debugging and convening of the video conference system of the national organization department, the quality of sound reproduction has been significantly improved, but there are still problems in some provinces and cities, mainly due to large noise, large distortion, unregulated level, and no frequency response. Uniform, unbalanced sound ratio, improper reverberation delay, etc.
1. The noise is large, which affects the clarity, softness and brightness of the sound. In severe cases, it will cover the sound of the venue. 1 noise floor. The noise floor occurs due to excessive gain, automatic gain control, impedance mismatch, and the like. 2 The microphone "bounces". Microphone is the first link of the sound reinforcement system. The quality of the signal directly affects the whole conference effect. Therefore, it should be reasonably selected according to its characteristics and performance, the characteristics of sound source reproduction and the relative relationship between sound sources. Settings. For speakers with strong breaks, you should use a microphone that is resistant to "sound".
2, the distortion is large, it is related to the nonlinear distortion of the device and human factors. It is characterized by hoarseness, breakage, and sharp thorns. In severe cases, it affects the clarity, softness, brightness, fullness and sense of the sound. The causes of distortion are various, such as the sensitivity of the microphone is too high, the placement position is not suitable, the microphone with phantom power is not powered properly, the level of the mixer is too large, the adjustment of the equalizer is not appropriate, and the device is The impedance between the two does not match.
3. The level is not standardized. No adjustments were made to the mixer, equalizer, etc. before commissioning, causing the signal level to be 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. The frequency response is uneven. It is related to the frequency response index and human factors of the device. For example, the microphone is pointing away from the sound source, the intermediate frequency and the low frequency attenuation are too much, and the microphone transmission line is too long, etc., all of which will affect the clarity, layering and fullness of the sound reproduction.
5, the sound ratio is out of balance. If the proportion of the sound between the general control room, the main venue, and the sub-meeting venue is out of balance, it will affect the balance of remote sounds restored by other sub-sites, resulting in a decline in the overall effect of the conference.
6, the reverberation delay is not appropriate. Different conference types and pickup environments have different requirements for reverberation and delay, so the parameters of reverberation and delay are adjusted according to acoustic characteristics. 1 The size of the venue affects the time of reflection and the sense of time in the sound field reverberation. 2 The reverberation time reflects the process of the sound diffusing 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 and modify the defects of certain sounds through audio processing equipment, but if it is not properly adjusted, it will be counterproductive. If the reverberation time is too long, the sound will have a "cloudy" feeling, so it is necessary to combine the actual and reasonable to add the reverberation effect to enhance the depth of the sound. The same is true for delay processing. 3 The frequency characteristics of the reverb reflect the reverberation effect and sound quality of the sound at different frequencies. To familiarize yourself with the frequency characteristics of the reverb, adjust the ratio of the microphone to the direct and reflected sounds to increase the realism and clarity of the sound. 4 Sound diffusion is a parameter that reflects the acoustic characteristics of the venue. It is necessary to properly set the microphone to compensate for the defects of the site's sound diffusion conditions, while avoiding the direction of the vibrating echo region and strong reflection.
Third, common interference
The interference generated by the audio signal during transmission is multi-faceted. Commonly, there are power supply interference, interference between devices, and light interference.
1. Power interference. Poor power supply grounding, poor ground contact between equipment and impedance mismatch, equipment power supply not "purified" processing, audio line and AC line with the same tube, the same trench or the same bridge, will cause clutter interference to the audio signal , the formation of low-frequency exchange "å—¡å—¡" 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. "Empty sound" is generated by the sound wave delay. If the microphone picks up both the sound source signal and the amplified sound restored signal, or two microphones with different sound source distances pick up the same sound source signal, or a microphone picks up The signal of the other microphone after the amplification is restored will cause a corresponding path difference and cause a delay. When these signals are superimposed, certain frequency components cancel each other out, forming an "empty sound."
3. Light interference. If the venue uses intermittent ballasts to activate the lights, the high-frequency radiation will be generated when the lamp is excited, and the microphone and its leads will be inserted in series, and a “beep†sound will appear; the microphone cable will be too close to the light line and will appear. "å±å±" sound. In addition, external high-frequency electromagnetic interference can also occur.
Fourth, the conference system audio interference processing method
The sound restoration of video conference should be based on the theoretical knowledge of acoustics, flexible adjustment of the mixer and equalizer according to different actual conditions, processing and beautifying the sound, making up for the defects of the sound field, creating an ideal acoustic environment; The limiter encounters a sudden large peak signal without overloading and no distortion, and at the same time avoids the compression limiter being in a compressed state for a long time, so that the sound connection is smooth and round.
For power supply interference, the following methods can be used: increase the power filter, use the resonant circuit to filter out harmonics, and “purify†the output power; the input and output lines of the signal are separated from the power line, and cannot be parallelly routed to avoid adjacent and Cross interference, mutual induction; use twisted pair power lines, so that the total magnetic flux generated by the two wires cancel each other out. For the "howling" phenomenon, the following methods can be adopted to avoid the formation of the inherent resonance point: reduce the sound amplification gain; use the equalizer or automatic feedback suppressor to reduce the amplitude of the "howling" frequency point; connect the frequency shifter or phase modulator, Use the offset frequency or phase to destroy the in-phase condition of the feedback sound and the sound source; adjust the speaker layout, change the direction of the microphone, and the distance between the two to avoid positive feedback. For the "empty sound" phenomenon, the following methods can be used to avoid the sound wave delay: use a directional microphone; turn off the ST switch in the mixer or pull down the extra microphone fader; adjust the sound source and its sound restored by the sound reinforcement proportion. For light interference, the following methods can be used to solve: the microphone line is away from the light line; the microphone line is shielded by the tube; and the microphone with strong anti-interference ability is adopted. To sum up, to make video conferencing better, it is necessary to improve the aesthetic appreciation of the sound and artistic accomplishment, and to conceive and creatively restore the sound, in order to improve the artistic expression of the sound.
Dongguan City Yuanyue Electronics Co.Ltd , https://www.yuanyueconnector.com