How do I go about using startBackground to get live microphone data, and process that data live?

Basically I want to get microphone data, put it through the B1 = bandpower(data,fs,freqrange1) method, and then output the result of the method. And I want it to do this constantly. How do I go about doing this? I've tried various documentation, but they don't explain well how to use the listener to get data into a variable. Here is what I have so far:

fs = 41000;

d = daq.getDevices;

dev = d(2);

s = daq.createSession('directsound');

ch = addAudioInputChannel(s, dev.ID, 1);

s.IsContinuous = true;

lh = addlistener(s,'DataAvailable', @(src,event) expr);  //This is where I am getting stuck. How do I make this so it feeds the data it recieves from the mic into a variable called data that I can then use to input into the bandpower method.

freqrange1 = [20,60];

freqrange2 = [60,100];

freqrange3 = [100,500];

freqrange4 = [500,1000];

freqrange5 = [1000,1500];

freqrange6 = [1500,2000];

freqrange7 = [2000,2750];

data = startBackground(s);

      while s.IsContinous

          B1 = bandpower(data,fs,freqrange1);

          B2 = bandpower(data,fs,freqrange2);

          B3 = bandpower(data,fs,freqrange3);

          B4 = bandpower(data,fs,freqrange4);

          B5 = bandpower(data,fs,freqrange5);

          B6 = bandpower(data,fs,freqrange6);

          B7 = bandpower(data,fs,freqrange7);

      end

Answer 1

[Walter Roberson]

"How do I make this so it feeds the data it recieves from the mic into a variable called data that I can then use to input into the bandpower method."

You do not do that.

When you use background operations, have you to get rid of the idea that the background operation is going to return data that you can store into a variable and then proceed to analyze. Instead you need to make the function you designate as the listener do the work.

Look at the first example for startBackground:

s = daq.createSession('ni');
addAnalogInputChannel(s,'cDAQ1Mod1','ai0','Voltage');
lh = addlistener(s,'DataAvailable',@plotData); 

function plotData(src,event)
     plot(event.TimeStamps,event.Data)
end

each time that data is available, the function plotData will be invoked with two arguments. The data is available in the Data field of the second argument.

For example you could code

      function do_the_thing

      [...]

      lh = addlistener(s,'DataAvailable', @(src, event) analyze_bandpower(event.Data));

      startBackground(s);

      function analyze_bandpower(data)      %nested so can use the shared variables freqrange*
          B1 = bandpower(data,fs,freqrange1);
          B2 = bandpower(data,fs,freqrange2);
          B3 = bandpower(data,fs,freqrange3);
          B4 = bandpower(data,fs,freqrange4);
          B5 = bandpower(data,fs,freqrange5);
          B6 = bandpower(data,fs,freqrange6);
          B7 = bandpower(data,fs,freqrange7);
      end

    end

[John Hackett]

How do I go about testing this? When I put it into the command window (with the necessary stuff first) it said it couldn't find the function?

It said this: Undefined function 'analyze_bandpower' for input arguments of type 'double'.

EDIT: I think I figured out how to run it, I just ran the script I made for it called test.m, however now I have the problem with it saying it can't find the variable fs... What is going on?

[Walter Roberson]

You would store it all in a file such as do_the_thing.m

Do not try to do this from the command line: the code for analyze_bandpower relies upon the freqrange* variables being shared variables. To be able to do this from the command line, you would need to pass the freqrange* variables to analyze_bandpower which you would have had to store into analyze_bandpower.m

[John Hackett]

I see. I think I have something now. At the very least the number get bigger when I speak. I ended up just putting the fs and freqrange variables into the function itself. For some reason even when I ran it as a file, it couldn't find the variables.