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Zero Cross Rate VAD

Question asked by benjaminws on Mar 31, 2016
Latest reply on Jun 8, 2016 by benjaminws



I am currently working on two noise reduction algorithms. One for background noise and one for non-stationary noise. The background noise algorithm is finished. For the none stationary noise I wanted to use a VAD. The VAD block from SigmaStudio does not function properly with non-stationary noise. I created a Zero Crossing Rate(ZCR) detector to classify frames as speech or noise.


The idea is to measure the zero crossings for a frame of 20ms. If the frame contains more than 25 zero crossings it will be classified as noise and it will not be routed to the output of the DSP. What I have implemented now is shown in the figure below.


It measures the zero crossings and routes the signal with 20ms delay to the output if it is speech. The ZCR "works". Speech is routed through and noise is classified as noise, however the noise is not classified as noise when the Max & Hold is reset. During the reset the rate is 0 and the noise is routed to the output causing a stutter.


The Yellow signal is the output  of the DSP. It is a noise only signal. The Blue signal is the Max & Hold. As you can see when the Max & Hold is reset the noise signal passes though for a brief period.


I want to create a buffer of 20 ms if it is possible, count the ZCR during 20ms and multiply the buffer by 1 or 0 for speech and noise respectively.



I changed the schematic to hold the value at the end of the frame just before the reset. Compare it to the threshold and let a 0/1 pass accordingly, use Hold blocks with a inverted timer to hold the 0/1 for 20 ms and multiply it by the delayed signal. This is on an ADAU1761. The project is attached, it works but not well. It seems some parts of the noise have the same number of ZC as the speech signal. The test signal is also attached.

ZCR 2.png