Today, most meeting rooms, theaters, etc., have a standard configuration, that is, audio, there are many uses, this problem need not be said more. But in addition to these uses, will the sound also encounter interference? Conference venue equipment includes conference terminals and related external equipment, and the types and functions of the equipment are basically the same. Therefore, the transmission processing of audio signals is divided into two parts:
The local sound is picked up by the microphone, the human voice is converted into a telecommunication number and sent to the mixing table. After amplification, mixing, distribution, sound quality modification and effect processing, it is divided into two channels: one signal is sent to the power amplifier at the local end for amplification and then restored to sound by the speaker; The other end is amplified by the mixer and then output by the speaker (AUX).
The other part: After the signal sent by the remote end is processed by the conference terminal, the audio signal enters the mixing table for processing, and then is sent to the power amplifier at the local end for amplification, and is restored to sound by the speaker. The above analysis shows that the mixer is the meeting point of each signal processing process, and how to adjust each key and function key of the mixer is the key to debugging.
The quality of sound restoration has been significantly improved, but there are still some problems in individual provinces and cities, mainly for loud noise, distortion, irregular level, uneven frequency response, sound proportion imbalance, mixing delay and so on.
Loud noise
This will affect the clarity, softness and brightness of the sound, and in severe cases will mask the sound of the venue.
① Background noise. When the gain is too large, automatic gain control is used, impedance mismatch, etc., background noise will be generated.
② The microphone "flutter" sound. The microphone is the first link in the PA system, and its signal quality directly affects the whole PA effect, so it should be reasonably selected and set according to the characteristics and performance of the PA system, reproduction characteristics and the relative relationship between the sound sources. For speakers with strong broken sound, a microphone should be used to prevent "flapping" sound.
Large distortion
This is related to the nonlinear deformation of the equipment and human factors. Symptoms are hoarse, broken, shrill, severe can affect the clarity of the sound, smoothness, brightness, fullness and sense of scene. There are many reasons for the distortion, such as excessive microphone sensitivity, improper placement, abnormal phantom power supply, excessive level adjustment of the mixer, improper adjustment of the equalizer, impedance mismatch between devices, etc.
Non-standard level
Devices such as the console and equalizer are not debugged before tuning, resulting in high or low signal levels. In addition, the direct connection of unbalanced output and balanced line input causes the signal level to drop.
Uneven frequency response
This is related to frequency response indicators and human factors, such as microphone pointing offset, IF attenuation is too large, microphone transmission line is too long, etc., will affect the clarity, layer sense, fullness of sound reduction.
Tone dissonance
If the sound ratio is out of whack in the main control room, main venue and sub-venue, it will affect the restoration of remote sound balance in other sub-venues, resulting in a decline in the overall effect of the conference.
False alarm delay
Due to the different requirements of reverberation delay time for different meeting types and audio environments, the reverberation delay parameters should be adjusted according to the acoustic characteristics.
① The size of the field affects the time sense of sound reflection and auditory time sense during reverberation.
② Reverberation time is the process of sound diffusion from the sound source through the surrounding absorption and reflection, the reverberation time depends on the size of the venue, the larger the distance, the longer the reverberation time. Audio processing equipment compensates and modifies certain sound defects, but improper adjustments can backfire. If the reverberation time is too long, the sound will produce a sense of "turbidity", so it should be combined with the actual situation, and reasonably add the reverberation effect to enhance the depth of the sound. Deferred processing also applies.
The frequency characteristics of reverberation reflect the reverberation effect and sound quality of sound at different frequencies. Be familiar with the frequency characteristics of reverberation, adjust the ratio of the microphone to the direct sound and the reflected sound, and improve the realism and clarity of the sound.
Sound diffusion is a parameter that reflects the acoustic characteristics of the site. The microphone should be set reasonably to make up for the defects in the sound diffusion conditions of the venue, and the vibration echo area and strong reflection direction should be avoided.
In the transmission process of audio signal, there are a lot of interference, common power interference, equipment interference, lighting interference and so on.
Power interference
Poor power grounding, poor ground contact between devices, impedance mismatch, power supply is not purified, audio line and AC wire with the same tube, the same ditch or the same bridge laying, etc., will cause clutter interference to the audio signal, forming a low-frequency AC "buzz" sound.
Interdevice interference
"Whistling" is caused by positive feedback between the speaker and the microphone, mainly because the microphone is too close to the speaker, or the microphone is pointed at the speaker. "Empty sound" is generated when the sound source is delayed, such as the microphone picks up the sound source signal and takes the signal restored by amplification, or two microphones at different distances from the sound source pick up the signal of the same sound source, or the signal of one microphone will produce the corresponding delay. After these signals are superimposed, certain frequency components cancel each other out, resulting in an "empty sound."
Lighting interference
The field uses the ballast mode to start intermittently the lamp, the lamp tube will generate high frequency radiation when excited, and through the microphone and its lead string, produce a "rattling" sound; If the microphone line is too close to the light line, there will also be a "squeak" sound; In addition, high-frequency electromagnetic can also cause interference.
Sound restoration of video conference should be based on the theoretical knowledge of acoustics, according to different actual conditions, flexibly adjust the mixer and equalizer, process and beautify the sound, make up for the defects of sound field, and create a more ideal acoustic environment; Adjust the compression limiter appropriately to meet the sudden large peak signal but not load and lose the weight, in order to make up for the lack of sound field and create a more ideal acoustic environment.