Hello, I used STFT spectrogram, when I plot the contour on time-frequency plot. The x-axis (time) starts from 25.4 not 0. I want it to start from 0. Below is the code I wrote. clear all; close all; clc; a=uigetfile('.txt'); b=dlmread(a); x=b(:,1); % data length is 3000 and sampling rate is 5000000. tt=0:0.2:(length(x)-1)*0.2; % The sampling rate is 5000000, multiplied it to find %time in micro seconds. % tt=0:0.2:(length(x)-1)*0.2; % time [y,f,t,p]=spectrogram(x,256,255,,5000000,'yaxis'); subplot(212) surf(t,f,abs(p),'EdgeColor','none'); axis xy; axis tight; colormap(jet); view(0,90); subplot(211) plot(tt,x) % plots the signal in time.