Sound restoration is an organic separation of technology and art, and its quality should be weighed from both objective and subjective aspects. With the advancement of informationization in organizational work, video conferencing systems in various provinces and cities have been extended to varying degrees. The design, selection, installation, and debugging of the entire system involve the influence of factors such as audio, video, power, and lighting. So, what are the causes of audio interference in conference systems, and what are the corresponding solutions?
The equipment at the sub-session includes conference terminals and related external devices, with similar types and functions. In summary, the transmission and processing of audio signals is divided into two parts:
The voice on this end is picked up by a microphone, converted into an electrical signal, and sent to the mixing console for amplification, mixing, distribution, sound quality enhancement, and effect processing. It is then split into two paths: one signal is sent to the power amplifier on this end for amplification, and then restored to sound through the speaker; the other signal is sent to the meeting terminal via the console's auxiliary output (AUX OUT) for processing and transmission to the remote end.
Remote signals are processed through the conference terminal, then the audio signals are sent to the mixing console for further processing. They are then amplified by the power amplifier at the local end and restored to sound via the speakers. The analysis shows that the mixing console is the focal point for processing various signals. Proper adjustment of the console's knobs and function keys is crucial during the tuning process.
The routine debugging and convening of national organizational department meetings have shown significant improvements in sound restoration quality. However, issues persist in some provinces and cities, primarily manifested as excessive noise, significant distortion, irregular levels, uneven frequency response, unbalanced sound ratios, and inappropriate reverberation delays.
Loud noise. It affects the clarity, warmth, and brightness of sound, and in severe cases, it can even overpower the sound in the venue.
Background noise. Excessive gain, the use of automatic gain control, and impedance mismatch can all lead to the presence of background noise.
② The "pop" sound of a microphone. As a component of the public address system, the quality of the microphone's signal directly impacts the overall effectiveness of the meeting. Therefore, it is essential to select and set it reasonably based on its characteristics and performance, the features of sound source reproduction, and the relative relationships between different sound sources. For speakers with strong popping, a microphone designed to prevent "popping" should be used.
2. Significant Distortion. It is related to the non-linear distortion of equipment and human factors. Characteristics include a hoarse, broken, and shrill sound that can, in severe cases, affect the clarity, warmth, brightness, richness, and presence of the sound. The causes of distortion are multifaceted, such as an overly sensitive microphone, improper placement, abnormal power supply to a phantom-powered microphone, excessive level adjustments on the mixer, inappropriate adjustments on the equalizer, and impedance mismatches between equipment.
3. Improper signal levels. Prior to debugging, the console, equalizers, and other equipment were not properly adjusted, resulting in signals that were too high or too low. Additionally, directly connecting unbalanced line outputs to balanced line inputs caused a drop in signal levels.
4. Inconsistent Frequency Response. It is related to the device's frequency response specifications and human factors, such as the microphone's direction deviating from the sound source, excessive attenuation of mid and low frequencies, and excessively long microphone transmission lines, all of which affect the clarity, layering, and richness of the sound restoration.
5. Sound Ratio Imbalance: If there is an imbalance in the sound ratio among the control room, the main venue, and the speaking sub-venues, it will affect the overall balance of remote sound recovery in other sub-venues, leading to a decline in the overall meeting effect.
6. Inadequate Reverb Delay. Different meeting types and microphone environments have varying demands for reverb and delay. Therefore, parameters for reverb and delay should be adjusted according to acoustic characteristics.
The size of the venue affects the time of reflection in the acoustic reverb and the perceived auditory time sense.
② The reverberation time reflects the process in which sound spreads from the source, being absorbed and reflected by the surroundings. It varies with the size of the venue, with larger spaces having longer reverberation times. Audio processing equipment is used to compensate and modify certain sound defects, but improper adjustments can have the opposite effect. If the reverberation time is too long, the sound can become "muddy," so it is necessary to differentiate theory from practical application and reasonably engage with the reverberation effect to enhance the depth of the sound. This is also true for delay processing.
The frequency characteristics of reverb reflect the echo effect and sound quality at different frequencies. To master the frequency characteristics of reverb, adjust the ratio of direct and reflected sound picked up by the microphone to enhance the authenticity and clarity of the sound.
④ Sound diffusion is a parameter reflecting the acoustic characteristics of the venue. It is essential to properly set up the microphone to compensate for the deficiencies in the venue's sound diffusion conditions while avoiding directions with flutter echo areas and strong reflections.
Interference in the transmission of audio signals is multifaceted, commonly including power interference, inter-device interference, and light interference, among others.
Power Interference.
Poor grounding of power supplies, poor contact between earth wires of equipment, impedance mismatches, unfiltered power supply treatment of equipment, and routing audio cables alongside AC wires in the same conduit, trench, or bridge can introduce noise interference to audio signals, resulting in low-frequency AC "humming" sounds.
2. Interference between equipment.
"Echo" is caused by positive feedback between the speaker and microphone, primarily due to the microphone being too close to the speaker or pointing towards it. "Hollow sound" is produced by the delay of sound waves. If the microphone picks up both the original sound signal and the amplified signal, or if two microphones at different distances from the sound source pick up the same signal, or if one microphone picks up the amplified signal of another, a corresponding path difference will be created, leading to delay. When these signals overlap, certain frequency components cancel each other out, resulting in "hollow sound."
3. Light interference.
If the lighting at the venue is started intermittently using ballasts, the tubes will generate high-frequency radiation when they are excited, which is then picked up by the microphone and its wires, resulting in a "tick-tick" sound; if the microphone wire is too close to the lighting wire, a "squeal" sound may also be produced; in addition, external high-frequency electromagnetic waves can also cause interference.
