Finding local minima

The following code snippet is something that I put together for a school project some time ago. In this project I was trying to apply some speech processing techniques to alter the pitch of a male speakers voice. At the time I was searching for the formants and trying to move them manually in the frequency domain.

I used this in conjunction with my local maxima code to find the position and the width (using local minima) of the speakers formants. If you give this function a 1-dimensional vector it will return both the indices in which each local minimum is found as well as it's amplitude.

I hope this code can find its way to other fun and exciting applications!

function [time,amp] = minima(signal, len)

%

% Finds the local minimum values of the given signal.

% 

% Usage:  [IND,AMP] = MINIMA(X, N);

% 

%         N is the number of points that need to be evaluated

%           (Normally equal to LENGTH(X))

%         X is the data 

%         IND contains the indices of X that contain the minima data

%         AMP contains the minima amplitudes

%

% Author: sparafucile17 10/02/2003

%Initialize data

index = 1;

prev = signal(1);

local_time = 0;

local_amp = 0;

prev_slope = 1;  %allow a maxima point at the second sample

%prevent length error

if(len > length(signal))

   len = length(signal)

end

%Loop through data and find local minimums

for loop_i=2:len

   cur = signal(loop_i);

   slope = cur - prev;

   if((cur < prev) & (prev_slope > 0))  %Positive slope and amplitude dips

      local_time(index) = loop_i-1;

      local_amp(index) = prev;

      index = index+1;

   end

   prev = cur;

   prev_slope = slope;

end

%After loop assign data to output variables

time = local_time;

amp = local_amp;

Rate this code snippet:

Rating: 0 | Votes: 0

posted by

Sign in

Search code

Ads

See Also

DSP Code Sharing > Finding local minima

Finding local minima

Finding local minima

ravitejaelx wrote: