MATLAB: Read single channel of multi-channel wav file

wav multi-channel single channel

Hi there. I have 2- and 4-channel wav files that I need to read in to Matlab, but I only need channel 1. The files are too large to load with a single wavread. I could load in chunks, but that will require a lot of changes to the rest of the code to only deal with partial data. And this is something that is supposed to be done in a couple of days… in my spare time…

I've been searching around for awhile now, hoping that there is a simple script that someone else has come up with to read a single channel from a multi-channel wav. But so far no luck. I thought I'd ask the question, in case someone else has come across something appropriate and can steer me in the right direction.

Suggestions would be very much appreciated. Thanks so much for your help.

Michael

Best Answer

There is no supplied method to do this.

http://www.mathworks.com/matlabcentral/newsreader/view_thread/302506

You can write your own routine and would not need to make many changes to your code. Call it wavread1.m or something like that. Make it a wrapper that loops reading chunks of data and throwing away the extra channels, until you get to the end.

Or if you need higher efficiency, then you will find that wavread is MATLAB source; you can trace through the parts of it that are actually used for your files, and edit those parts to not read in the extra channels (if that makes sens for the chunk) or to throw away the extra (if necessary for that kind of chunk.)

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If the .wav file is a stereo audio file, then wavread can read them in as separate channels.

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I believe AUDIOPLAYER underwent a poorly, possibly undocumented, change at some point. The AUDIOPLAYER object now makes use of an ASYNCIO object, which I do not believe was always the case (although again I am not sure).

Probing your problem a little further, it appears that the isplaying method does not become false until the event queue is flushed no matter how long intervening computations take between PLAY and ISPLAYING.

    obj = audioplayer(rand(44.1e3, 1), 44.1e3);
    play(obj);
    t0 = clock;
    cnt = 0;
    while etime(clock, t0) < 2
      cnt = cnt+1;
    end
    isplaying(obj)

At a minimum this needs to be documented, and seems like a bug that you should report.

Looking at the code, the isplaying method of an AUDIOPLAYER object is essentially a wrapper for the isOpen method of an +asyncio.Channel object, which is essentially a wrapper for the proprietary asyncioimpl.Channel.isOpen method. Based on as far as TMW will let us look, there is no way to know why this requires the event queue to be flushed. A hint might be the fact that +asyncio.Channel object has an event called "Closed". Maybe the proprietary asyncioimpl.Channel object also has an event that it is listening for (which would require a flush of the event queue), but that is just a guess.

A simple work around is to use some of the available portaudio implementations for presenting sounds.

Best Answer

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