【转帖】Matlab信号上叠加噪声和信噪比的计算

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function [Y,NOISE] = noisegen(X,SNR)

% noisegen add white Gaussian noise to a signal.

% [Y, NOISE] = NOISEGEN(X,SNR) adds white Gaussian NOISE to X. The SNR is in dB.

NOISE=randn(size(X));

NOISE=NOISE-mean(NOISE);

signal_power = 1/length(X)*sum(X.*X);

noise_variance = signal_power / ( 10^(SNR/10) );

NOISE=sqrt(noise_variance)/std(NOISE)*NOISE;

Y=X+NOISE;

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function [Y,NOISE] = add_noisem(X,filepath_name,SNR,fs)

% add_noisem add determinated noise to a signal.

% X is signal, and its sample frequency is fs;

% filepath_name is NOISE‘s path and name, and the SNR is signal to noise ratio in dB.

[wavin,fs1,nbits]=wavread(filepath_name);

if fs1~=fs

wavin1=resample(wavin,fs,fs1);

end

nx=size(X,1);

NOISE=wavin1(1:nx);

NOISE=NOISE-mean(NOISE);

signal_power = 1/nx*sum(X.*X);

noise_variance = signal_power / ( 10^(SNR/10) );

NOISE=sqrt(noise_variance)/std(NOISE)*NOISE;

Y=X+NOISE;

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function snr=SNR_singlech(I,In)

% 计算信噪比函数

% I :\original  signal

% In :noisy signal(ie. original signal + noise signal)

snr=0;

Ps=sum(sum((I-mean(mean(I))).^2));%signal power

Pn=sum(sum((I-In).^2)); %noise power

snr=10*log10(Ps/Pn);

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clear all; clc; close all;

[filename,pathname]=uigetfile(‘*.wav‘,‘请选择语音文件：‘);

[X,fs]=wavread([pathname filename]);

[Y,NOISE] = noisegen(X,10);

subplot 311; plot(X);

subplot 312; plot(NOISE);

subplot 313; plot(Y);

mn=mean(NOISE)

snr=SNR_singlech(X,Y)

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clear all; clc; close all;

[filename,pathname]=uigetfile(‘*.wav‘,‘请选择语音文件：‘);

[filename1,pathname1]=uigetfile(‘*.wav‘,‘请选择噪声文件：‘);

filepath_name=[pathname1 filename1];

[X,fs]=wavread([pathname filename]);

[Y,NOISE] = add_noisem(X,filepath_name,10,fs);

subplot 311; plot(X);

subplot 312; plot(NOISE);

subplot 313; plot(Y);

mn=mean(NOISE)

snr=SNR_singlech(X,Y)