[Octave-bug-tracker] [bug #56889] Incorrect encoding results from uint8 vector to wav file

[Rik]

Follow-up Comment #10, bug #56889 (project octave):

In audiowrite, the translation from [0, 255] to the range [-1.0, +1.0] for
passing to libsndfile *is* compressing the range.

First this code,


  if (args(1).is_uint8_type ())
    bias = scale = std::pow (2.0, 7);


which sets bias and scale at 128.  And then


for (int i = 0; i < audio.rows (); i++)
  {
    for (int j = 0; j < audio.columns (); j++)
      {
        double elem = (audio.xelem (i, j) - bias) / scale;
        data[idx++] = std::min (std::max (elem, -1.0), 1.0);
      }
  }


The value 255 is translated to (255 - 128) / 128 = 127/128 which is not 1.0.



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