Matlab real-time audio plotting in a GUI

Hi Community,

I encountered the following two problems using the audioPlayerRecorder object. I hope to display some processed variable based on input audio and provide audio alarming if such variable above a certain threshold. I followed instructions here: https://www.mathworks.com/help/audio/gs/real-time-audio-in-matlab.html Right now the audio processing is conducted in an infinite while loop. The code is roughly working however still have some issues

Problem 1): since the current procesing time is long. When running the code, the audio player queue always has some underruns. I do not know how to solve this. I tried Malab multi-threading while the performance is even worse

Problem 2) I tried to design a GUI for the existing code, when pressing the 'start' button, the code should run and real-time display the variable in the area speicifed by the GUI settings. However, when pressing the start button, the loop not conduct properly, should I use timer for such process?

Thank you in advance for any help.

Best,

Larry

[Mario Malic]

Hi, I haven't worked much with such object, but maybe I can give some hints.

I will try to explain your problem 1: if you want to capture a signal for 20 seconds with sample rate of 100, meaning, in total you will get 2000 samples. There is a thing called buffer size which says, what number of samples MATLAB is going to take before processing it (whatever you want to do to signal). For the sake of the example, let's say, buffer size is 500 samples.

You start acquiring signal with sound device, MATLAB waits until 500 samples are in the buffer (~5 seconds, with sample rate from above) and then it gives you signal (data) to process with your algorithm. As you are processing it, MATLAB is still acquiring signal in the background. Once analysis/processing is finished, your algorithm wants to process more signals. If there isn't a signal to process, then you have an underrun which means that MATLAB has to wait for another 500 samples to feed them into your analysis. This is not really a bad thing, but it's not as close to the real-time as it can(should) get which depends on your problem.

I wouldn't go into details, how would you organise your acquired data as I am not super familiar with the audiodevice object.

I don't think you should use timer as it may slow down the acquisition process.

If I manage to, I could create an example app soon.

[Liwei Wang]

Hi Mario @Mario Malic, Thank you for your kind reply. Actually, I hope to build a system continuous conducting audio recording and playing (unless manually stopped by user). I use the AudioPlayerRecorde object. I noticed that when the processing algorithm is complex, the player part sometimes have underruns since whether I trigger the player function depends on the processing result of input audio. The player part just plays some beeping sound as alarm (generated by sine() function). It is strange as the player just plays some pre-generated tones while still have underruns. And The processing algorithm cannot be minimized. I am wondering is there any suggestions for solving this? (Maybe by decreasing the sampling rate?)

For the UI part, I tried to use the UI figure function. Is it possibe to permanently display the processing result (SNR value dots with lines between each dot)? Somes docs said a while() loop cannot be conducted by a buttonPressed() function?

Thank you in advance for any help.

Best,

Larry

[Matthew]

Hi,

I am facing a similar issue. I am creating an application that plays real time audio and plots the spectrum with some other functions. Also using the AudioPlayerRecorder.

Here is a quick list of things I have tried that have not seemed to work:

• Using the background thread or parallel processing toolbox. Unfortunately neither the AudioPlayerRecorder or the GUI can be pushed to a background thread, meaning that an update to the GUI results in an underflow in the audio.
• Timer. I have a successful demo of using a timer to periodically play/record samples. However I've run into the same issue regarding underflows with GUI underflows. This solution works to a point, but does not scale as the GUI demands increase.

The big issue that I am facing is the fact that the AudioPlayerRecorder and anything to do with the GUI seems to fight over the same resource without an easy way to multithread the two operations.

I am open to all ideas to get this to work.

Thanks,

Matt