MATLAB: How can i recording audio immediately

acquisitionaudio acquisitionaudiorecorderdata acquisitionMATLAB

I'm working with audiorecorder object for recording audio, with this code:

recObj = audiorecorder(8000,16,1)
recordblocking(recObj, 1);
audioarray = getaudiodata(recObj);
plot(audioarray)

I noticed that the registration doesn't start immediately, but it waits about 0.4/0.5 s. You can see this problem with this image:

I need that it starts immediately after i run the recording (also because i would like to create small (acquisition windows, about 0.2 s).

I also tried to use pause() and resume() but it has the same problem.

What can i do to solve this problem?

Thanks in advance

Best Answer

Hi,

Given below is a command which will open example for you which will help you record the audio immediately.

openExample('audio/ReadFromMicrophoneAndWriteToAudioFileExample')

Moreover, you can also modify the default properties of your audioDeviceReader object to reduce latency.

openExample('audio/CalculateLatencyDueToDeviceBufferExample')

You can also go through this link for any information.

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Hi Ali,

I work at MathWorks in the Audio System Toolbox team. I can't exactly replicate your experiement as I don't have your hardware, but I could notice a few possible sources of issues.

In your code you seem to be acquiring simultaneously from two different devices using the default audio drivers (typically DirectSound or WASAPI on Windows). That gives you no guarantee of synchronous acquisition for L and R. The two devices themselves may be triggered asynchronously by the operating system, giving you an arbitrary new delay between the two signals every single time you run your script.

The simplest guarantee of a synchronous acquisition comes from acquiring different channels of the same device, ideally using its ASIO driver instead of the default one. ASIO drivers guarantee synchronous multi-channel acquisition.

At a minimum, you should try something like the following, which gets L and R from the first two channels of the same device:

recObj = audiorecorder(fs, 16, 2, deviceID);

Even better, you may want to try audioDeviceReader object in Audio System Toolbox, which supports ASIO drivers and is routinely used out there for latency-sensitive acoustic measurements. See for example the first example from the reference doc page (Read from Microphone and Write to Audio File):

deviceReader = audioDeviceReader('Driver','ASIO','NumChannels',2);
setup(deviceReader);
fileWriter = dsp.AudioFileWriter('myTwoChannelRecording.wav');
disp('Recording...')
tic;
while toc < 5
    acquiredAudio = deviceReader();
    fileWriter(acquiredAudio);
end
disp('Recording complete.')
release(deviceReader);
release(fileWriter);

audioDeviceReader also gives you the ability to acquire whatever arbitrary pair of channels from your device through what we call channel mapping.

You'll find more detailed explanations on audio measurement latency under Audio I/O: Buffering, Latency, and Throughput.

I hope this helps.

Regards,

Gabriele.

MATLAB: Record audio and get data in real time

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.

Best Answer

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