Ambient sounds, such as air conditioners, projector fans, and humming sounds of light ballasts, do not have the property of rubbing and plosives, which is a collection of composite frequencies of different intensities. Ambient sense technology can detect whether the frequency component of the audio signal is ambient sound. The ambient sound detection algorithm can be applied to ANC (Ambient Noise Compensation).
Application scenario description:
In the public area sound reinforcement system, if the level value of the background music or the paging sound source is constant, the sound pressure level of the environmental noise is often uncertain. When there are many people, the sound pressure level of the environmental noise is relatively large, and may be the background music or paging source is masked off (the masking effect of the sound); when the number of people is small or empty, the ambient noise level is small, and the sound pressure level of the background music or the paging source is large. Therefore, a DSP processing module capable of accurately determining the magnitude of the environmental noise and accurately adjusting the volume of the background music or the paging source is required. The DSP module is an ANC (Ambient Noise Compensation) module.
The traditional ANC (Ambient Noise Compensation) works:
An environmental noise detection microphone is installed in the public area to measure the ambient noise level, and the result is returned to the environmental noise compensation module of the digital audio processing platform (DSP). The other input to the ambient noise compensation module is usually background music or a paging source. Through the setting of the ambient noise compensation module, when the ambient noise exceeds the preset threshold, the background music or paging source level will be increased according to the set ratio and time to ensure that the background music or paging source is clear enough. The ground is heard (the program source is ≥25dB than the ambient noise, which ensures that the person hears the sound of the program source clearly); When the ambient noise is less than the threshold set in advance, the level of the background music or the paging source will be set. The ratio and time decay are fixed to ensure that the background music or paging source does not make the volume too loud.
Application of environmental detection technology:
The seemingly traditional ambient noise compensation circuit has been perfect, and the program source signal compensated by the traditional ambient noise compensation module is increased, and then amplified by the speaker, and then picked up by the ambient sound pickup microphone (in the same sound field), thus an infinite loop will be formed, and the source signal of the program will continue to increase and cannot be effectively adjusted. The solution to the traditional ambient noise compensation is to keep the ambient sound pickup microphone away from the speaker. The consequence of the ambient noise compensation module is not accurate enough.
The environment detection algorithm cuts off the relationship between the ambient sound pickup microphone and the speaker, and uses an adaptive filtering method to tell the ambient sound pickup microphone to filter the audio signal amplified by the speaker, and only pick up the environmental noise, so that ensure accurate processing of ambient noise compensation, while the position of the ambient sound detection microphone is randomly placed.
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