How to Suppress Noise in Video Conferencing System?

In daily life, we often encounter the problem of microphone noise, noise makes the volume of sound system not big (transmission gain decreases), sharp and harsh voice makes it hard to hear, even if it is good quality, expensive sound system also escape this problem. In general, analysis of the reasons for the scream needs to be combined with on-site analysis, and the main reasons are more common:

• The speaker is too far away from the microphone, resulting in a soft tone, which increases the sensitivity and volume of the microphone. Due to the limitation of transmission gain, there will also be noise.
• The speaker installation position is not good. Speakers placed in the two corners of the conference room, sound, due to the height of the microphone and the height of the microphone, direct sound or reflected by the wall sound is easier to enter the microphone to produce noise.
• The walls around the meeting room scene are made of plastic aluminum plates and other materials to form a smooth interface, with strong sound reflection. Strong reflection sound into the microphone, amplification by the system to produce positive feedback, causing noise.
• The scene space of the conference room is narrow, and the sound wave diffusion is poor, and the sound wave is easy to reflect into the microphone and cause a scream.
• The conference sound system is not equipped with feedback suppressor, which is easy to produce noise.

There is a peak frequency in the sound characteristics of the speaker, the microphone will keep receiving the peak, the sound will keep playing back the peak, many times a second, the peak will be infinitely amplified until the equipment is damaged.

ITC technology research and development department gives several solutions to the noise, mainly including the following:

• When decorating sound box, should make the direct sound that listens to sound area obtains sound directly. In general, speaker hanging is a good way to get direct sound in the room.
• In the acoustic design or decoration, the audience area should be reasonably treated with sound absorption. The seats and floor should use sound absorption materials, and the primary reflective surface corresponding to the main speaker should be treated with sound absorption to reduce the sound energy returned from the audience.
• Use good ITC microphones and ITC conference speakers. Good conference room audio and microphone in the factory before the sound characteristics have been tuned very smooth, the waveform is too smooth slope is small, there will not be a narrow band of peaks, scream rarely occur.
• The distance between the speaker's mouth and the microphone in the conference room should be within 15 cm, and the microphone should wear a BOP cover.
• Speakers should be placed symmetrically with the central axis of the room, so as to create a harmonious and even sound field environment.
• itc sound column can be used as sound reinforcement box, because of its strong directivity, reduce reverberation interference, provide strong direct sound, at the same time can compensate for distant sound attenuation, make sound field evenly distributed, reduce sound feedback. ITC line array speaker system can also be used, which can well solve the horizontal and vertical plane coverage, strong direction, and reliable suppression of acoustic feedback.
• Using the feedback suppressor, ITC feedback suppressor can quickly scan and automatically find the feedback frequency, and can automatically generate a set of signals with the same frequency polarity of the opposite signal to eliminate or remove the noise frequency signal, so as to suppress the feedback, improve the transmission gain.
• Using frequency shifter, the basic idea of using ITC frequency shift method to reduce acoustic feedback is to destroy the in-phase condition of feedback sound and original signal by means of offset frequency and suppress the self-excited oscillation of the system. The frequency shifter can be connected in series to the mixer. Increase the frequency of the input audio signal by 3Hz, 5Hz, or 7Hz, and then output, after passing through the peripheral equipment to the power amplifier, through the loudspeaker into the sound field. If the sound re-enters the microphone, after the frequency shift device processing, the frequency of the audio signal will increase 5Hz(or 3Hz, 7Hz) by the speaker into the sound field, because of the frequency change, so will not produce peak noise at the same frequency.