Help required with audio in MATLAB
I'm 开发者_JAVA百科trying to write an .m file to extract energy features from an audio track but I seem to be having trouble in its implementation:
% Formula for calculating RMS
[f, fs, nb] = wavread('Three.wav');
frameWidth=441; %10ms
numSamples=length(x);
numFrames=(numSamples/1);
energy(frame)=0;
for frame=1:numFrames,
startSample=(frame-1)*frameWidth+1;
endSample=startSample+frameWidth-1;
% Calculate frame energy
for i=startSample:endSample
energy(frame)=energy(frame)+x(i)^2;
end
end
I run that file in MATLAB and get the following error:
??? Attempted to access x(2); index out of bounds because numel(x)=1. Error in ==> myrms at 12 energy(frame)=energy(frame)+x(i)^2;
Any help would be much appreciated.
You should be using f
instead of x
, since f
is the actual signal loaded from your .wav file. The variable x
was probably just some other scalar in your workspace, which is why you were getting the error you saw.
There are a few other corrections/improvements that should be made to your code. First, as Paul R pointed out, you need to correct how you compute numFrames
. Second, energy
should be initialized as a vector of zeroes. Third, you can reduce the inner for loop to a one-line vectorized operation.
Here's how I would rewrite your code (EDIT: Based on comments, I have updated the code to save a few extra variables computed in the loop):
[y, fs, nb] = wavread('Three.wav'); %# Load the signal into variable y
frameWidth = 441; %# 10 msec
numSamples = length(y); %# Number of samples in y
numFrames = floor(numSamples/frameWidth); %# Number of full frames in y
energy = zeros(1,numFrames); %# Initialize energy
startSample = zeros(1,numFrames); %# Initialize start indices of frame
endSample = zeros(1,numFrames); %# Initialize end indices of frame
for frame = 1:numFrames %# Loop over frames
startSample(frame) = (frame-1)*frameWidth+1; %# Starting index of frame
endSample(frame) = frame*frameWidth; %# Ending index of frame
frameIndex = startSample(frame):endSample(frame); %# Indices of frame samples
energy(frame) = sum(y(frameIndex).^2); %# Calculate frame energy
end
Shouldn't this line:
numFrames=(numSamples/1);
be something like:
numFrames=(numSamples / frameWidth);
or possibly:
numFrames=((numSamples + frameWidth - 1) / frameWidth);
?
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