MATLAB Answers


Using mp3write

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'
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.


Image Analyst
on 9 Apr 2012
I don't have mp3write so I can't try anything. What toolbox is it in, or where did you get it?
Daniel Shub
on 9 Apr 2012
mp3write comes from

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1 Answer

Daniel Shub
Answer by Daniel Shub
on 9 Apr 2012
 Accepted 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.
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, ...);


Walter Roberson
on 9 Apr 2012
I haven't checked the older documentation, but the documentation of the current wavwrite() range limits is the same as my memory of the limits. It could be that before it did not warn about +1 exactly though.
Daniel Shub
on 23 Apr 2012
Looking at this question again, it appears David uses MATLAB 6.1, so it is not a recent change in wavwrite.

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