About recording narration in PowerPoint 2007 and onward
When you record narration in PowerPoint, what you get will depend on which version you use. If you choose to record narration in PowerPoint 2007, you'll see this dialog box:
Change Quality opens another dialog box where you can choose from a fairly wide range of sampling rates, each with stereo or mono choices. The choices you make can a big effect on the size of the recorded narration files. The lower the sampling rate, the smaller (but lower quality) the file. Stereo records two tracks so selecting stereo will result in files approximately twice the size of mono recordings.
You also have the choice of linking or not, and choosing the folder to link to.
(Note that this gives you a fully pathed link, even if you're saving the linked narration files to the same folder as the PPTX itself. This is probably a bug. It can cause links to souds to break if you move the sound files to a different folder or computer.)
The narration files, whether linked or embedded, will be in WAV format; meaning uncompressed ... large.
If you choose to record narration in PowerPoint 2010 and later, you'll see a different dialog box:
Perhaps Microsoft felt that all the choices in 2007 scared users. If so, they've certainly solved that problem, leaving us with the following setup:
- Narration is recorded at 64kbps (higher than the default in 2007, but no options for higher/lower rates).
- Narration files are embedded (no option to link).
- Narration is saved as WMA format files (compressed, so they're smaller).
- Period. Other options? None.
Not bad as options go, but sometimes a higher or lower sampling rate is preferable (when we want higher quality sound or need smaller files).
How do the different settings interact?
When you open a file with narration recorded and embedded in PowerPoint 2007, PowerPoint 2013 tells you that it can optimize and compress the media if you let it convert the file to the 2013 format.
If you do that without making any other changes, you still have WAV files in the PPTX but the PPTX file size will be smaller, perhaps by half the size of the original embedded WAV files. Most probably, PowerPoint has "downsampled" from its original sampling rate to 88kbps.
If you open the same file and then choose PowerPoint 2013's option to optimize for compatibility, the WAV sounds get converted to MP4. In one test, the resulting MP4 was sampled at 100kbps and was larger than the WAV from the previous step (but still smaller than the original WAV recorded by PowerPoint 2007).
Can I get more control over the sound quality and other options?
Yes. Your friends at PPTools (that's us) have written a PowerPoint add-in called PPTools Narrator. It's free for now.
You record your narration in your own preferred audio recording software where you have total control over the sampling rates and other factors, and can easily edit out glitches and add effects. Once you're satisfied with the narration, you split it into multiple individual files, one for each slide that needs narration, and name them in a special way. Audacity is a great free audio editing program and makes splitting up the audio track very simple (Narrator's help file includes insructions). Narrator then marries the audio files to the slides in a logical way.