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Poor wideband MOS results can be the result of recording narrowband content (speech sample) in wideband format.  This can be confirmed using the freeware Audacity tool:

• Run a Google search to find the free Audacity download online and install.
• Open the *.WAV file in question with Audacity.
• Select the region of audio to analyze (most likely the entire speech sample).
• Select Analyze → Plot Spectrum.
• The frequency appears on the graph's x-axis:
  • Narrowband - shows to 4000 Hz
  • Wideband - shows to 8000 Hz

This sample was recorded in narrowband format with narrowband content:

This sample was recorded in wideband format with wideband content:

This sample was recorded in wideband format with narrowband content.  This sample exhibited poor MOS due to the fact that the recording format did not support the test content.