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'

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.

[Image Analyst]

I don't have mp3write so I can't try anything. What toolbox is it in, or where did you get it?

[Daniel Shub]

mp3write comes from http://www.mathworks.com/matlabcentral/fileexchange/13852-mp3read-and-mp3write

Answer 1

[Daniel Shub]

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, ...);

[Walter Roberson]

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]

Looking at this question again, it appears David uses MATLAB 6.1, so it is not a recent change in wavwrite.