[knowledge] What are the problems in audio security monitoring?

Many network cameras provide audio support. Whether they are built-in microphones or/and microphone/line input jacks, audio signals are transmitted through the network. Most traditional surveillance systems do not have sound. Like early silent movies, people can only see silent sounds. Image, many monitoring systems now require integrated audio. What are the technical challenges faced by the pickups in the right angle of security monitoring and what should they pay attention to in actual operation?

First, the three major technical problems in the audio security monitoring pickups

1. The audio monitoring technology has been developing slowly for a long time, and noise processing is difficult.

Since vocals and noise are easily conflated after amplification, audio monitoring does not achieve its purpose and meaning even if it is noise that is picked up by pickups. Pickup noise reduction needs to solve two problems, one is to reduce the noise from the circuit itself, and the other is to reduce the interference from environmental noise. The noise of the circuit itself is relatively easy to solve, and the environmental noise problem is more complicated and difficult to solve. Low-level environmental noise can be automatically monitored by noise and feedback suppression. This technology can suppress some of the ambient noise. However, in strong noise environments such as highways, DSP noise suppression must be used to achieve higher requirements. At present, the most advanced voice noise reduction algorithm can only reduce noise by about 20dB in the case of ensuring less distortion.

2, remote audio monitoring is difficult

From the physical principles of sound propagation in the air, we know that most people speak loud sounds at 50 decibels and spread distances of about 30 meters. Noise on busy roads is basically at 60 decibels, and the sound of speech can easily be “overwhelmed”. This is why everyone is getting louder and louder in a noisy environment so that the other party can hear it. However, the sound energy of a person's voice spread to 100 meters away has already tended to be zero. No matter how magnified, it is useless. With the mixing of environmental noises, the processing of speech becomes more difficult. The laser pickup can solve the problem of hearing long-distance sound, but the cost is very high, the sound quality is poor, and the directionality is strong. It cannot be widely promoted in the audio monitoring field and can only be used in the criminal investigation field.

3, good pickups are expensive

Microphone microphone head as a key component of the pickup, its performance directly affects the quality of the sound. Poor mics cost a few cents, and good mics cost tens of thousands. In order to obtain better sound quality, you must use a high-grade microphone head, and its cost accounts for more than half of the total cost of the pickup. Coupled with the high cost of DSP chips for back-end noise processing, the price of high-end pickups has remained high. This is why karaoke microphones are a few hundred dollars, and why CCTV announcers use tens of thousands of microphones.
 

Second, the network camera sound pickup poor solution

1: first determine whether the network camera audio input is: LINEIN (linear level)

2: If it is to determine the LINE audio input port, then check whether the microphone power supply is normal, check the connection of the pickup is correct.

If the above two cases are determined, the sound quality recorded by the webcam is still very vague or has no sound?

1: First, check the pickup audio signal output connection, the general network camera audio input connector is 3.5 headphone connector, then the corresponding pickup audio signal line, it must be transferred into a 3.5 headphone connector.

2: It should be noted that although you plug in a 3.5 headphone connector, but the 3.5 connector, he is divided into two channels and single channel points, that is, stereo and mono, check your 3.5 connector is dual channel or Single channel.

3: If the confirmation is mono, then the positive electrode of the pickup is connected to the positive electrode of 3.5, and the negative electrode is connected to the negative electrode. If you have two channels, then there will be a three-core cable, the negative electrode of the pickup is connected to the negative electrode of 3.5, and the positive electrode is connected to the other two wires corresponding to the 3.5 connector, which are the left and right channels respectively.

4: There is also a situation where the audio input of some brands of network cameras now has both: LINE and MIC input, that is to say an audio input port, he may be left channel is LINE right channel is MIC, In such a situation, you cannot connect the left and right channels together to connect the positive pole of 3.5. For example, if the negative electrode is connected to the negative electrode, the positive electrode is connected to one of the 3.5 connectors, and then listen to the sound. If it is not normal, change it to another audio cable. But can't carry on the parallel connection of the left and right channels, also forbid to use the monophonic 3.5 joints, must use the dual-channel joint.
 

Third, pickups access video optical transceivers and DVR should pay attention to matters

The indicators that should be noted in the pickup optical transmitter are bandwidth, impedance, input/output level, maximum output power, signal-to-noise ratio, and nonlinear distortion. However, due to the relatively inconsistent application of audio, such as: probes (pickers) arranged at monitoring points, background music in parks, or intercoms between the two places, their requirements for audio transmission are all different. Should be considered as appropriate according to the actual situation.

In addition to the number of channels, the audio selection also divides one-way audio and two-way audio according to actual needs. Where one-way audio is applied, such as transmitting the signal of the pickup in the monitoring alarm, it only transmits the audio signal from the front end to the control center and applies bidirectional audio. Places such as audio toll stations and other places.