record audio and get data in real time

Hello, i want to make a recorder in real time, and i get data every 0.01 second with recording parameters(Fs = 8000, nbits = 16 bits, nbChannel = 1), so i want to get the 80 samples (every 0.01) second to analyse them and apply my work. i used audiorecorder object but no result, when i try to get data it is empty. Thank you

[Geoff Hayes]

dz - please show the code that you have written to use the audio player. Have you created a GUI to start the recording and display the results in real-time? Provide some context as to what you are attempting.

[Geoff Hayes]

dz's answer moved here

clear all 
clc 
close all 
global dt dtt c 

%%Create a timer object:
time_rec = 2; 
recObj = audiorecorder(8000,16,1);   
set(recObj,'TimerPeriod',0.01,'TimerFcn',@VADML); 
record(recObj,time_rec)

%%below function is to try to read data by samples for each 0.01 sec 
function [dt] = VADML(h,~) 
    global dt dtt c 
    % Get data from each sample 
    dt = getaudiodata(h) 
    % compute energy 
    c=0; 
    if mod(length(dt),80)==0 
        c=c+1 
        dtt=dt(1:80) 
    end 
end

Answer 1

[Geoff Hayes]

dz - a couple of things to note. You don't need to declare some of your variables as global if you nest your VADML function within a parent function. For example,

 function mainScript
     dt  = [];
     c   = 0;
     dtt = [];

     % create the timer 
     % ...
     function VADML(h,~)
         dt = ....;
         % etc.
     end
 end

Using globals is fine, but you can avoid it with nested functions and (as in above) there is no need to return dt from VADML since you are updating a local variable in the parent function workspace.

I suspect that you aren't getting any data because you are using record instead of recordblocking. The latter does not return control until recording completes. Using record will not block and so once you call it once, the code will continue on its way and exit the main function or script before it has a chance to do anything. So you want to block to prevent this from happening.

I'm a little unclear on the code in your VADML function

 function VADML(h,~) 
    % Get data from each sample 
    dt = getaudiodata(h);
    % compute energy 
    c=0; 
    if mod(length(dt),80)==0 
        c=c+1;
        dtt=dt(1:80); 
    end 
 end

Why do you reset c each time this function is called? Won't dtt be the same on each iteration as you are always grabbing the first 80 samples? Note that getaudiodata returns all of the collected data to that point in time. So dt will "grow" on each iteration: 80, 160, 320, etc. I suspect that you want to extract the latter 80 samples.

Finally, the 0.01 second rate may be too ambitious given that you are trying to extract some data and process it. If I just do

    function VADML(h,~) 
        % Get data from each sample 
        dt = getaudiodata(h) ;
        c = c + 1
    end

I find that c iterates from 1 to 151 (using R2014a on a MacBook Pro) and not the expected 200 times. You may need to relax this 0.01 second requirement and bump this up to 0.1 seconds.

[dz despe]

Thank you for your answer, i tried using function parent but it does not work, anyway, forget all variables, my main idea is to GET data (here data is 80 samples values) every 0.01 second,when running code below the for 1 second (so 8000 samples as total data), the variable data_each_sample is a vector of length(8000), why its not a vector of length (80) ? i used recordblocking for 0.01 but no result, i want for example when time = 0.01, data_each_sample(1:80) = whole_data(1:80) time = 0.02, data_each_sample(1:80) = whole_data(81:160) time = 0.03, data_each_sample(1:80) = whole_data(161:240) . . time = 1 sec, data_each_sample(1:80) = whole_data(8000-80+1:8000) Wokring in REAL Time of corse. see my new code below, i remove all unecessary variables:

if true
 clear all
clc
close all
global data_each_sample
% data_each_sample = read data (values of 80 samples)
% every 0.01 second 
time_rec = 1; % total time for recording
recObj = audiorecorder(8000,16,1); % create rec object
set(recObj,'TimerPeriod',0.01,'TimerFcn',@VADML); 
record(recObj,time_rec)
recordblocking(recObj,0.01)

if true
 function VADML(h,~)
 global data_each_sample 
 data_each_sample = getaudiodata(h,'int16')
end

Thank you again my friend. end end

[Geoff Hayes]

dz - I don't understand why you are calling record (for one second) and recordblocking (for 0.01 seconds). Something like the following will work "better" but still not behave as expected

 function [sampleData] =  mainScript

    sampleData = {};

    atSample = 1;
    atPeriod = 1;

    time_rec = 5; % total time for recording
    recObj = audiorecorder(8000,16,1); % create rec object
    set(recObj,'TimerPeriod',0.01,'TimerFcn',@VADML); 

    recordblocking(recObj,time_rec);

    function VADML(h,~)
        samples = getaudiodata(h);
        sampleData{atPeriod} = samples(atSample:end);
        atPeriod = atPeriod + 1;
        atSample = length(samples)+1;
        get(h,'CurrentSample')
    end
 end

It won't work as expected since it does not seem to be able to keep up with the samples that are being collected i.e. it runs slower and so when the timer callback fires, more than 80 samples have been collected since the last time.

Why is it necessary to collect and process those 80 samples immediately once collected? Why can't the processing be deferred?

[Geoff Hayes]

Perhaps try this

 function [sampleData] =  mainScript

    sampleData = {};

    atSample = 1;
    atPeriod = 1;
    fs       = 8000;
    timerPer = 0.01;
    sampleSize = floor(fs*timerPer);

    time_rec = 5; % total time for recording
    recObj = audiorecorder(fs,16,1); % create rec object
    set(recObj,'TimerPeriod',timerPer,'TimerFcn',@VADML); 

    recordblocking(recObj,time_rec);

    function VADML(h,~)
        samples = getaudiodata(h);
        sampleData{atPeriod} = samples(atSample:sampleSize+atSample-1);
        atPeriod = atPeriod + 1;
        atSample = atSample + sampleSize;
    end
 end

We ensure that we only get 80 samples each time the callback fires but it may still lag. When I tried this just now, in the five seconds, I was only able to get the samples for the first 3 seconds or so...

[David Clark]

Thank you for this answer! It really helped with a project I am working on. (Simultaneously sampling EKG data while recording audio).