How do i plot an audio file with an interval in ms?

Hi! I am currently using matlab 2021 version. I want to know how would I plot an audio file in the interval of 20 miliseconds of my choice for example the audio recording is 10 seconds long but, I want to plot only from 0 to 20 miliseconds. How would I do that? This is my code right now

recObj = audiorecorder;
Fs=8000;
filename = sprintf('myAudioData.wav');
disp('Start speaking.')
recordblocking(recObj, 10);
disp('End of Recording.');

doubleArray = getaudiodata(recObj);
audiowrite(filename,doubleArray,Fs);

[x,Fs] = audioread('myAudioData.wav');
[m,n]=size(x);
dt=1/Fs;
t=dt*(0:m-1);
idx = (t>=1.030) & (t<1.032); 
selected_t = t(idx);
selected_x = x(idx,:);
plot(selected_t, selected_x);

Answer 1

[Scott MacKenzie]

Using the sample frequency of the audio data (Fs), this code will extract and plot the first 20 ms:

[x, Fs] = audioread('AudioSample.wav'); % test audio file

ts = 1 / Fs;         % duration of each sample
n = round(0.02/ts);  % number of samples in 1st 20 ms
plot(x(1:n));        % plot 1st 20 ms of audio file

[Michael Sugiarto]

what if the interval of 20 ms is in the middle?

[Michael Sugiarto]

the middle of the audio say 3.000s to 3.020

[Scott MacKenzie]

In this case you need to compute the start and end index of the segment of interest. This can be done as follows:

[x, Fs] = audioread('AudioSample.wav');
ts = 1 / Fs;           % duration of each sample

% start and end time of segment of interest (seconds)
t1 = 3.000; 
t2 = 3.020; 

% start and end index in audio data of segment of interest
idx1 = round(t1/ts)+1;
idx2 = round(t2/ts)+1;

% plot it!
plot(x(idx1:idx2));         

[Michael Sugiarto]

Thank you so much!!

[Scott MacKenzie]

@Michael Sugiarto, you're welcome. Good luck.

Answer 2

[KSSV]

idx = t <= 20*10^-3 ; 
plot(t(idx),x(idx))