Sound recovery is an organic separation of technology and art, and its quality should be weighed from both objective and objective aspects. With the progress of the degree of information technology in organizational work, the video conferencing system in various provinces and cities has been extended to different degrees, and the design, purchase, installation and debugging of the entire system have touched the influence of audio, video, power, lighting and other elements. So what are the reasons why the conference system presents audio interference, and how to deal with it?

　　The equipment of the sub-venue includes the conference terminal and related external equipment, and the type and function of the equipment are similar. In general, the transmission and disposal process of audio signals is divided into two parts:

①After the local sound is picked up by the microphone, the human voice is converted into an electrical signal and sent to the mixing table to stop amplification, mixing, distribution, audio quality modification and effect processing, and then divided into two ways: one signal is sent to the local power amplifier to stop amplification and then recovered to sound by the speaker; The other signal is sent to the conference terminal by AUX OUT of the sound mixing console for disposal and then transmitted to the remote end.

②After the signal sent from the remote end is processed by the conference terminal, the audio signal enters the mixing table to stop processing and disposal, and then sends to the power amplifier at the local end to stop amplifying and recover to sound by the speaker. The above analysis shows that the mixer is the gathering point of each signal processing and disposal, and how to adjust the knobs and function keys of the mixer is the key in debugging.

　　Throughout the national organization of departments conference system routine debugging and holding meetings, the quality of sound recovery has made significant progress, but there are still problems in individual provinces and cities, mainly manifested as large noise, distortion, irregular levels, uneven frequency response, sound proportion imbalance, improper reverberation delay and other problems.

1. Loud noise. It affects the clarity, gentleness and brightness of the sound, and can mask the sound of the venue in severe cases.

①Background noise. Due to excessive gain, automatic gain control, impedance mismatch, etc., will present background noise.

② Microphone "flutter" sound. The microphone is the first link of the PA system, and the quality of its signal directly affects the effect of the entire conference, so it is necessary to choose and set reasonably according to its characteristics and performance, the characteristics of the sound source reproduction and the relative relationship between the sound sources. For speakers with strong broken sound, a microphone that prevents "flapping" should be used.

2、Large distortion. It is related to the nonlinear distortion of equipment and human factors. It is characterized by hoarseness, breakage, sharpness and harshness, which will affect the clarity, gentleness, brightness, fullness and sense of scene of the sound. The causes of distortion are many, such as the sensitivity of the microphone is too high, the placement is not suitable, the microphone with the phantom power supply is not normal, the level adjustment of the mixer is too large, the adjustment of the equalizer is not appropriate, and the impedance between the devices is not matched.

3、The level is irregular. The signal level is too high or too low if the tuning of equipment such as the mixer and equalizer is not stopped before debugging. In addition, the unbalanced line output is directly connected with the balanced line input to form the signal level drop.

4、The frequency response is uneven. It is related to the frequency response index of the equipment and human factors, such as the direction of the microphone deviates from the sound source, too much attenuation of the medium frequency and low frequency, and the microphone transmission line is too long, which will affect the clarity, layer and fullness of the sound recovery.

5、The sound is out of proportion. If the sound proportion between the main control room, the main venue, and the sub-venue of the speech is out of whack, it will affect the balance of the remote sound in other sub-venues, and constitute the overall effect of the meeting.

6、Improper reverberation delay. Different meeting types and pickup environments have different requirements for reverberation and delay, so the parameters of reverberation and delay should be adjusted according to the acoustic characteristics.

① The size of the venue affects the time of reflection in the reverberation of the sound field and the auditory sense of time.

② Reverberation time reflects the process of sound absorption and reflection from the sound source. The reverberation time depends on the size of the venue. The larger the space, the larger the reverberation time. Some sound defects should be compensated and modified by audio processing equipment, but improper adjustment will backfire. If the reverberation time is too long, the sound will have a sense of "turbidity", so it is necessary to separate the theory and reasonably participate in the reverberation effect to enhance the depth of the sound. The same goes for delayed handling.

③ The frequency characteristics of reverberation reflect the reverberation effect and sound quality of sound at different frequencies. To be familiar with the frequency characteristics of reverberation, adjust the proportion of direct sound and reflected sound picked up by the microphone to increase the realism and clarity of the sound.

④Sound diffusion is a parameter that reflects the acoustic characteristics of the venue. It is necessary to set the microphone reasonably to compensate for the defects of the sound diffusion conditions of the venue. At the same time, the direction with shivering echo area and strong reflection should be avoided.

　　The interference generated by audio signal in the transmission process is many aspects, common power interference, interference between devices, lighting interference and so on.

1, power interference.

Poor grounding of the power supply, poor ground contact and impedance mismatch between the devices, the power supply of the equipment is not "purified" disposal, the audio line and the AC wire are laid with the same tube, the same ditch or the same bridge, which will cause clutter interference to the audio signal, constituting a low-frequency AC "buzz" sound.

2, interference between devices.

"Whistling" is caused by the positive reaction between the speaker and the microphone, the main reason is that the microphone is too close to the speaker or the microphone is pointed at the speaker. "Empty sound" is generated by acoustic delay, if the microphone picks up both the sound source signal and pick up the signal recovered by amplification, or two microphones with different distances from the sound source pick up the signal of the same sound source, or a microphone picks up the signal of the other microphone after the amplification recovery, it will produce the corresponding road difference and constitute a delay. When these signals are superimposed, certain frequency components cancel each other out, forming an "empty sound."

3. Lighting interference.

If the venue uses the ballast intermittently started lamp, the lamp tube will generate high-frequency radiation when aroused, and will pass through the microphone and its leads, presenting a "rattling" sound; If the microphone line is too close to the light line, it will also show a "squeak" sound; In addition, the external high-frequency electromagnetic will also cause interference.