输出信噪比计算

function snr_vec = fftdisto(x, C, varargin)

% FFTDISTO compute distortion of sinusoidal signal

% SNR_VEC = FFTDISTO(X,C,N)

% input:

% x signal vector

% C number of full sinusoids in X

% N length of signal to consider (must be a power of 2)

% only N last samples in x are used in fft

% output vector:

% 1 pwr signal power [dB] (amplitude 1 --> 0dB)

% 2 sndr signal-to-noise+distortion ratio (DC omitted) [dB]

% 3 snr only uncorrelated noise (harmonics + DC omitted) [dB]

% 4 sdr signal-to-distortion (only harmonics, noise+DC omitted) [dB] % 5 tdh total harmonic distortion [%]

% NOTE: make N > 6 * C -->

% considers only approx. first N/2C harmonics,

% rest are treated as noise

if nargin > 3

fprintf('nargin = %d\n', nargin)

error('Too many arguments.');

end

N = length(x);

if nargin == 3

if varargin{1} > N

error('N exceeds length(x)');

end

lenx = N;

N = varargin{1};

if lenx > N

x(1:(lenx-N)) = [];

end

end

N2 = 0.5 * N;

if log2(N2) ~= round(log2(N2))

error('N must be power of 2');

end

if C > N2

error('C > N/2 (signal frequency > sampling frequency');

end

if N < 6*C

% warning('computing less than 3 harmonics!');

end

a = abs(fft(x))/N2; % amplitude vector

p = a .* a; % power vector

dc = 1; % index of DC component

sig = C+1; % index of signal

harm = (2*C+1):C:N2; % indices of harmonics

noise= 1:N2; noise([ dc sig harm ]) = [];

% indices of noise

sp = p(sig) + 1e-100; % signal power

dp = sum(p(harm)) + 1e-100; % distortion power

np = sum(p(noise)) + 1e-100; % noise power (not including distortion)

snr_vec = zeros(1,5);

snr_vec(1) = dB10(sp);

snr_vec(2) = dB10(sp/(np+dp));

snr_vec(3) = dB10(sp/np);

snr_vec(4) = dB10(sp/dp);

snr_vec(5) = 100*sqrt(dp/sp);

matlab中的信噪比

(2011-03-22 19:52:49)

分类：学习

标签：

信噪比

杂谈

以高斯噪声为例：若有用信号s(n)的最大幅度am，要求得到的信噪比为p，则p=10log10[(am^2)/b^2]，用这个公式反推出高斯噪声的方差b^2，若s(n)单通道实信号，则Matlab程序就是x=s+b*randn(size(s))；若s(n)是正交双通道信号，则Matlab程序就是

x=s+b/sqrt(2)*randn(size(s))。

如果s(n)是一个N行、2列的复信号，前后两列各表示实部和虚部，则b/sqrt(2)*randn(size(s))产生的也是N×2的高斯分布噪声，实部和虚部的方差均为

b/sqrt(2)。实部和虚部分别产生也可以，但不能用

b*randn(size(s))。第一，如果这样产生噪声，那么最终信号的信噪比应该用

p=10log10[(am^2)/(2*b^2)]；第二，不能用size(s)，应该用size(c)，c为s(n)的实（虚）部列矢量的长度。

Matlab中计算信噪比方式：

%===========================Happy===== ==============================%

function snr=SNR(I,In)

% 计算信号噪声比函数

% by Qulei

% I :original signal

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

% snr=10*log10(sigma2(I2)/sigma2(I2-I1))

[row,col,nchannel]=size(I);