Audio Noise Reduction Technology For High Precision Keyword Spotting System

With the rapid development of artificial intelligence(AI)technology and Internet of things(IOT)technology,voice interactive devices are more and more used in daily life.As the front-end wake-up module of voice interactive devices,the application of keyword spotting(KWS)system has also been popularized.As the input module of the whole voice interaction equipment,the keyword recognition system has high requirements on its recognition accuracy and power consumption.With the increase of the application scenarios,the noise interference in the environment will lead to the decrease of keyword recognition accuracy.How to maintain the high precision of keyword recognition under the interference of ambient noise is an important challenge in the application of this field.Filter has been playing a very important role in the field of audio signal processing,it can effectively reduce the interference of ambient noise in audio signal,improve the recognition accuracy of keyword spotting system.In order to effectively de-noise the audio signal and finally deploy in the keyword spotting system,the designed filter should have the characteristics of high precision and easy integration.At the same time,in order to be applied to the scene with different noise interference,it is necessary to ensure that the filtering parameters of the audio noise reduction processing module can be adjusted to meet the filtering requirements of different ambient noise.In view of the above problems,a specific research on audio noise reduction technology based on high-precision keyword recognition system is carried out by this paper,and an audio noise reduction filter chip with high precision,easy integration and adjustable parameters is designed.The main contents of this paper are as follows:(1)The circuit of switched capacitor filter with adjustable parameters is designed.The filter is designed with Switched Capacitor(SC)circuit in this paper.Under standard CMOS process,the ratio precision of on-chip capacitance is very accurate,so the switched capacitor filter has good audio signal noise reduction precision and circuit integration.The coefficient of the transfer function of the filter system is related to the ratio of the capacitor in the circuit,and the capacitor in the circuit can be configured according to the needs of the actual scene to achieve the filtering function.In the case of complex noise,this paper uses multi-level cascade to achieve high order filter to fit complex ambient noise characteristics.(2)Verification of keyword spotting system using audio noise reduction chip technology.The core circuit of the chip is a switched capacitor filter circuit with adjustable parameters.The circuit composes of complementary CMOS switch,capacitor and fully differential operational amplifier.The overall design is a differential structure.After the circuit design and layout drawing,the whole chip has completed under the SMIC 0.18 μm process node with an area of 1.061mm~2.(3)Verification of keyword spotting system using audio noise reduction chip technology.According to the design scheme proposed in this paper,an audio signal denoising module is added to the KWS system to verify the feasibility of the scheme.In the KWS system,the audio signal before and after noise reduction is recognized.The results show that the recognition accuracy can be improved by 14.04% after denoising the audio signal superimposed with ambient noise.