If you import a stereo audio file into your Presenter '09 presentation and find that the volume level is lower, quieter, or softer than expected, the left and right channels of the audio file may be out of phase. A stereo audio file that is out of phase will not play properly when it is imported into Presenter '09.
How to determine if an audio file is out of phase
- Open your audio file in an audio editing program, such as Audacity (which is a free tool).
Zoom in to view a small section of the audio waveform.
- If the left and right audio channels display exact opposite waveform images (mirror images), as shown in the screenshot below, then your audio file is out of phase.
How to correct an audio file that is out of phase
- Open your audio file in an audio editing program, such as Audacity.
Split the stereo track, so that each channel can be modified independently of the other.
Invert one of the channels.
Export the modified audio to a WAV or MP3 file.
- Return to your PowerPoint presentation, and remove the previously imported audio file that is out of phase.
Import the modified audio file into your presentation.
Here is a video screencast of this process using Audacity: