CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of TW application serial No. 110102441 filed on Jan. 22, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a delay time estimation method and a system thereof, and more particularly to an echo delay time estimation method and system thereof.

2. Description of the Related Art

As video conferences becomes popular for business meetings, demands for equipment for the video conferences are also raised. During video conferences, often a part of sound coming out of a speaker is picked up by a microphone, initiating a loop of sounds between microphones and speakers. This sound oscillation is an echo, disturbing the quality of the video conferences.

An important step to cancel the echo of the video conferences is to estimate an echo delay time. Once obtaining the echo delay time, most video conference software will be able to suppress the echo with its own algorithm. However, a common echo delay time estimation method is time consuming and complicated, creating quite a computational complexity on the video conferences equipment.

For instance, a common echo cancelling system would suppress an echo by measuring an acoustic impulse response of an environment. First the echo cancelling system will broadcast a testing impulse signal through a speaker, and then a microphone will pick up a received signal. The echo cancelling system will then calculate a cross-correlation of the testing signal and the received signal in time domain. However in real spaces, environmental factors can change over a period of time. Time dependent environmental changes in temperature and relative object positions can increase margins of error for the aforementioned cross-correlation.

The common echo cancelling system will also be affected by the quality of video conferences equipment. For instance, if the testing signal impulse cannot be cleanly broadcasted because of problems of a speaker, it will be more difficult to calculate cross-correlation of the testing signal and the received signal, causing an extra cost for a computing system.

Furthermore, the common echo cancelling system often uses an adaptive filter to suppress the echo. The adaptive filter would include a least mean square (LMS) filter and a recursive least squares (RLS) filter. The least mean square (LMS) filter will estimate the gradient of the received signal through each iteration. Since the gradient estimation technique is a stochastic gradient descent (SGD) method, the estimation is time consuming and complicated to calculate. The recursive least squares (RLS) filter will recursively adjust the weights of corrections for an estimation. The recursive least squares (RLS) filter takes less time to calculate an estimation, and calculations of the recursive least squares (RLS) filter are even more complicated than the least mean squares (LMS) filter's, causing the computing system to process extra computational loads.

The common echo delay time estimation technique suffers as its margins of error are affected by environmental changes during video conferences, as its computational complexity increases whenever the speaker used in the video conferences cannot produce clean testing signals, and as its computational complexity also increases by using complicated filters to calculate.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide an echo delay time estimation method and system thereof to mitigate a problem of an echo canceling system wherein the computational complexity is heavy and margins of error is wide.

The echo delay time estimation system includes a pre-processing device, a dynamic vector calculating device, and a cross-correlation calculating device.

The pre-processing device receives a testing signal and a received signal, and respectively executes a time to frequency analysis to generate a testing signal spectrogram and a received signal spectrogram.

The dynamic vector calculating device is electrically connected to the pre-processing device, receives the testing signal spectrogram and the received signal spectrogram, and respectively executes a characteristic signal dynamic detection calculation for the testing signal spectrogram and the received signal spectrogram to generate a testing signal characteristic dynamic vector and a received signal characteristic dynamic vector.

The cross-correlation calculating device is electrically connected to the dynamic vector calculating device, receives the testing signal characteristic dynamic vector and the received signal characteristic dynamic vector, executes a cross-correlation vector calculation for the testing signal characteristic dynamic vector and the received signal characteristic dynamic vector to generate a cross-correlated vector, and calculates an echo delay time according to the cross-correlated vector.

Furthermore, the echo delay time estimation method includes the following steps:

receiving a testing signal and a received signal;

respectively executing a time to frequency analysis for the testing signal and the received signal to generate a testing signal spectrogram and a received signal spectrogram;

respectively executing a characteristic signal dynamic detection calculation for the testing signal spectrogram and the received signal spectrogram to generate a testing signal characteristic dynamic vector and a received signal characteristic dynamic vector;

executing a cross-correlation vector calculation for the testing signal characteristic dynamic vector and the received signal characteristic dynamic vector to generate a cross-correlated vector; and

calculating an echo delay time according to the cross-correlated vector.

The present invention uses addition and subtraction to calculate shifting of the cross-correlated vector in frequency domain. By avoiding executing cross-correlation calculations in time domain, the echo delay time estimation method is able to ensure a better delay time estimation accuracy as calculations in frequency domain will not be affected by non-linear sounds and non-linear environmental changes in the time domain. Therefore, the echo delay time estimation method may estimate an echo delay time with stability and tolerance.

Since the echo delay time estimation method only executes addition and subtraction calculations in the frequency domain to obtain the cross-correlated vector, the echo delay time estimation method does not need to execute convolution calculations in the time domain, and is able to simplify calculations to alleviate some computational complexity.

