# find power of signal

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Daemian on 23 Dec 2014
Edited: Image Analyst on 24 Dec 2014
Hi, how do i find total power of signal from a wav file and display it on axes ? I currently only have this.
[myRecording,fs] = audioread('filename.wav',[1,2*8000]); %fs = sample rate
Nsamps = length(myRecording);
t = (1/fs)*(1:Nsamps); %Prepare time data for plot
%Do Fourier Transform
y_fft = abs(fft(myRecording)); %Retain Magnitude
y_fft = y_fft(1:Nsamps/2); %Discard Half of Points
f = fs*(0:Nsamps/2-1)/Nsamps; %Prepare freq data for plot
%Plot Sound File in Time Domain
plot(handles.normalLies,t, myRecording)
xlabel(handles.normalLies,'Time (s)')
ylabel(handles.normalLies,'Amplitude')
%Plot Sound File in Frequency Domain
plot(handles.fttLies,f, y_fft)
xlim(handles.fttLies,[0 20])
xlabel(handles.fttLies,'Frequency (Hz)')
ylabel(handles.fttLies,'Amplitude')

Shoaibur Rahman on 24 Dec 2014
In time domain: for discrete signal x(n)
Instantaneous power = x(n)^2
Average power = (1/N) * sum(x(n).^2)
N = data length or period

Image Analyst on 24 Dec 2014
Edited: Image Analyst on 24 Dec 2014
The total power would be a single number - a scalar. Do you mean power as a function of frequency, like the spectrum like you'd get from pwelch(), or fft()? From the help: "pxx = pwelch(x) returns the power spectral density (PSD) estimate, pxx, of the input signal, x, found using Welch's overlapped segment averaging estimator. " pwelch() is in the Signal Processing Toolbox. There is a webinar on spectral analysis that hopefully you can find on the Mathworks web site that goes over it and the fft in detail.

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