Screencast: Using Audacity to trim down podcasts

As I was jogging away on the treadmill last night, it occurred to me that the 75-minute lecture that I was listening to for school was primarily dead space. People pause between sentences, and generally ramble on like I do. A lot of that space can be eliminated, so the lecture that I was listening to could probably be much shorter than it was.

What I’m going to show you how to do with this screencast is save yourself a lot of time, but still get the exact same information. And maybe reduce the classes that you are listening to to something more like a 45-minute workout instead of a 75-minute workout.

The screencast does have some information that is specific to the system that my school uses to distribute podcasts, but if you skip ahead to about 1:25 then you can get right to the juicy bits that anyone can use.

Abbreviated transcript follows:

  1. Download Audacity from SourceForge. You want to get at least the 1.3 series, as the 1.2 series doesn’t have all of the filters you need.
  2. Open the MP3. Do a Select All to get the entire thing.
  3. From the Effects menu, choose Truncate Silence. For a well-normalized lecture, a threshold of -20db is probably best, but you can play with it to get it how you like it. This one effect will normally trim down your MP3 by a good 15-35%, without losing any of the useful data.
  4. If you want to crunch a bit more out of it, use the Change Tempo effect. This clips out some of the speech data and may make the words sound choppy. Alternatively, you can use Change Speed, which actually squishes the waveform to make it play faster. This makes the instructor sound like Mickey Mouse, but doesn’t cause them to clip and chop. A combination of the two, with the latter at no more than 10%, is recommended.
  5. Go under Preferences and make sure your MP3 export settings are set to be the same as the source bitrate. For Tegrity lectures, that’s 16 kbps.
  6. Use Export > MP3 from the File menu to save the resulting MP3.

That’s it! The whole process should take you less than 5 minutes per track, but should save you far more time than that when it comes time to listen. You can squeeze more class time and more information into the same workout time. And, I’ve found that eliminating the stilted drawl of some of my professors helps me to not lose focus on the workout or the material.

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Rick Osborne

I am a web geek who has been doing this sort of thing entirely too long. I rant, I muse, I whine. That is, I am not at all atypical for my breed.