MATLAB: Using mp3write

MATLABmp3write

I have used mp3write with success often in the past but lately I am getting "clipping" errors.
Here is a typical session:
>>  mp3write(y,Fs,16,'BuiltUpWave',1);
Warning: Data clipped during write to file:temp.wav 
> In wavwrite>PCM_Quantize at 287
    In wavwrite>write_wavedat at 309
    In wavwrite at 138
    In mp3write at 53
Can't init outfile 'c:\matlab6p1\apps\musicalsoundanalysis\matfilesmusicwaves\BuiltUpWave.mp3'
where
c:\matlab6p1\apps\musicalsoundanalysis\matfilesmusicwaves
happens to be the current folder and the variables involved are:
>> whos y Fs
  Name      Size                Bytes  Class     Attributes
    Fs        1x1                     8  double              
    y         1x33075            264600  double
Can anyone show me what I am doing wrong? Thanks.

Best Answer

The warning comes from the standard MATLAB function wavwrite. Given some other questions on Answers, I think wavwrite may have changed its behavior recently (although I haven't checked). Basically, a vector that has a +1 value will be clipped (by a single quantization unit). My guess is that mp3write is scaling things to be +/-1 and that this causes the clipping warning.
You should report the warning on the fex page: http://www.mathworks.com/matlabcentral/fileexchange/13852-mp3read-and-mp3write
As a work around on line 53 (according to your error message) should be a line like
wavwrite(x, ...);
you can replace this with.
wavwrite(0.99*x, ...);
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