Captivate Audio Output Settings Comparison – Part Two – Encoding Frequency

Mark — Sat, 26 Jul 2008 15:33:48 +0000

This is part two of a series of articles written with the express purpose of finding the best filesize-to-quality ratio for publishing voiceover audio out of Captivate. Part One can be found here. At the end of the series I’ll provide my thoughts/opinions, followed up by a tabular summary of the facts. And, of course, a recommended setting.

More information about the testing methodology can be found in part one of the series.

Encoding Frequency

There are three encoding frequency settings available in Captivate:

: Captivate Encoding Frequency Options

For this test, I settled on the following settings for each and simply changed the encoding frequency.

Encoding Bitrate: 48kbps
Encoding Speed: 5 (the default)

As with the last test, each swf was published with the three settings shown on the slide:

Published SWF Files

Published File Size Comparison

As you can see, no matter which encoding frequency is selected the published swf is roughly the same file size. However, if you listen closely you’ll hear that the clarity is slightly better when using the 44.10khz setting. This is not so evident in comparison to the 22khz sample, but definitely if you first listen to the 11khz and then the 44khz. So, it seems that it makes no sense, based on my little test here, to ever drop the encoding frequency to below the default setting of 44khz. I guess I’ll have to try with a larger audio file to see if that makes a difference? Or should I redo these tests with a source audio file that has a short musical intro followed by voiceover audio? Perhaps that would yield more definitive results? If anyone with in-depth knowledge of the meanings behind these settings reads this please comment and/or email me if you can explain some of this stuff better so I can include it here.

Summary

For years I’ve always seemed to settle on using an encoding bitrate of 48kbps. Not due to any real testing other than some quick, under-tight-deadline-pressure, testing. To my ears, this comparison seems to confirm that 48kbps is the proper setting for voiceover audio as it yields good clarity as well as good file size. Listen to the 128kbps sample, followed immediately by the 48kbps sample, and then the 32kbps sample. You’ll hear a definite difference between the three, but the 48kbps is still very good. The 32kbps is somewhat muffled. I don’t think any students/users would know the difference between the upper two, but the 32kbps is muffled enough that it would bother me over time.

In the next part of this series I’ll demonstrate how varying the encoding speed setting effects things.

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Captivate Audio Output Settings Comparison – Part Two – Encoding Frequency