What is hanming window? What is the function of adding a hanmming window?

What is hanming window? What is the function of adding a hanmming window?

 

1.What is hanming window?

A:I am engaged in speech recognition. Let me talk about it from the perspective of speech.

 

Generally, the voice signal ranges from 10 ms to 30 ms. we can regard it as stable. To process the voice signal, we need to add a window to the voice signal, that is, only the data in the window is processed at a time. Because the actual voice signal is very long, we cannot and do not have to process very long data at a time. The wise solution is to take a piece of data for analysis each time, and then take a piece of data for analysis.

 

How can I retrieve only one piece of data? One way is to construct a function. This function has a non-zero value in a certain range, and the value of 0 in other intervals is such a function. The shape of the main part is sin (x) in the range from 0 to Pi, and the rest is 0. such a function is multiplied by any other function f. Only a part of F has a non-zero value.

 

Why is it like this? We will then perform FFT on the data in the Hamming window. It assumes that the signal in the window represents a periodic signal. (That is to say, the left and right sides of the window should be largely connected together.) Generally, there is no obvious periodicity in a small segment of audio data. After the Hamming window is added, the data shape will feel a little cyclical.

 

Because the Hamming window is added, only the data in the middle is displayed, and the data information on both sides is lost, when the window is moved, only 1/3 or 1/2 windows will be moved, in this way, the data lost from the previous frame or two frames is reflected again.

 

In short, the hanming window is a function, and its shape is like a window. Therefore, similar functions are called window functions. I hope you can understand.

 

2.Function of adding a hanmming window

Now I am reading g.723.1. I am just getting started with Speech Encoding,

It is found that before LPC analysis on the signal, multiply the signal by a Hamming window,

Multiplication: multiply the signal directly by the value in a hammingwindowtable. What is the function of this window?

If the bandwidth is restricted, the signals in the time domain should be convolutionalized. If you do not understand, please kindly advise.

 

Because we want to process a segment of an infinite long sequence, we must add a window to collect this sequence.

 

The typical window size is 25 ms, and the frame shifting is 10 ms. The Hamming window function is

W (n, α) = (1-α)-α cos (2 * pI * n/(N-1), 0 108n N-1

Generally, α is 0.46.

Can someone explain this function? I really don't understand. Thank you.

 

Because the direct truncation of the signal (adding a rectangular window) will lead to frequency leakage, in order to improve the frequency leakage, non-rectangular windows are usually added with a hanming window, because the amplitude-frequency characteristics of the hanming window are the large side-lobe attenuation, the peak attenuation between the main side and the first side-lobe can reach 40 dB.

 

For example: aw.wavread('jiasiqi.wav '); %reads the audio signal jiasiqi.wav into subplot (, 1), and % allocates the canvas. There are two images in one image. This is the first plot (); title ('original signal '); % plot the original signal, that is, add the grid line N = 256 to the original waveform grid of the preceding audio signal; % set the length of the short-term Fourier transformation, it is also the Hamming Window Length H = Hamming (n); % set the Hamming window for M = 1: N % to intercept the signal with the Hamming window, the length is n, mainly to reduce the barrier effect caused by truncation, such as B (M) = a (m) * H (m) Endy = 20 * log (ABS (FFT (B ))) % perform Fourier transformation, take its modulo value, that is, the amplitude-frequency characteristics, then use dB to indicate subplot (, 2) % to allocate the canvas, and the second figure plot (y ); title ('short-term spectra '); % draw short-term spectral grid % add grid lines

 

What is hanming window? What is the function of adding a hanmming window?