Source: http://feeds.gawker.com/~r/lifehacker/full/~3/XwjGXC1GORM/how-do-i-speed-up-hundreds-of-audio-files
I have unabridged Asimov audiobooks that are great, but read at a mind-wrenchingly slow pace. I can boost an MP3's speed 20 percent using Audacity, but I have around 250 MP3s. How can I process these files all at once?
Signed,
Sped-Up Sci-Fi Fan
Dear Sped-Up,
If you were a command line geek, or knew one who owed you a favor, speeding up all of your audiobooks at once would probably be a five-minute affair. That said, it's not that difficult to set up a "Chain" in Audacity (which runs on Windows, Mac, and Linux) that you can apply to multiple files from inside the program.
You already know the effect you want to apply to all your MP3s: a 20 percent "speed" increase, where pitch and tempo are sped up at the same time and no correction is applied, as if you were just playing a tape faster. Most folks would go for "ChangeTempo" instead, because a ChangeSpeed on a normal narrator sounds pretty Alvin & The Chipmunks. Still, you described your audiobook narrator as "mind-wrenchingly slow." Let's set this speed-up as a chain by hitting the File menu in Audacity and selecting "Edit Chains"—it's down near the bottom of the menu.
Update: If you don't see "Edit Chains" in your File menu, you may need to upgrade to the latest Beta release, as opposed to Stable.
You'll get a new window with two "chains" pre-loaded as examples. Hit the "Add" button in the lower left, give your new "chain" a name like "Asimov Audiobook Speed-Up," and hit OK. You'll notice that there's a single command listed for your new chain in the right-hand window, but it's just an empty "END" command. Double-click that command, or hit "Add." You'll get a pop-up window asking you to select a command and edit its parameters.
Click on the image below for a larger view.
I double-clicked "Change Speed" in the commands window, and it auto-filled the fields above with the basic command line operation to run a speed change on files. It's set to 0 percent, however, which won't do us much good. Hit "Edit Parameters," and you'll get a slider and numeric input you can use to set a percentage for the speed-up or slow down. You can use the automatic vinyl conversion tools if you were copying a 33 1/3 record to some other format, but we already know our number, 20 percent, and we'll stick with that. I'm not sure how the Preview button is supposed to work, but let's just leave it alone. Hit OK, hit OK back at the command chooser, and OK once more at the Edit Chains box, where you can see your one-line Asimov Audiobook Speed-Up chain.
Back in Audacity, close any files you happen to have open for editing. Hit the File menu and select "Apply Chain," and in the dialog that pops up, select your Asimov chain and click the "Apply to Files" button. Choose the audio files you want to run through your speed wringer. Audacity isn't the A-number-One most stable program I've ever used, so I'd recommend running around 10 files at a time through your chain—then again, maybe you can plug in 30 files at a time and just deal with the crashes when they happen, since it processes them one at a time anyways.
Audacity will run through your files and convert them, one by one, and show you its progress. Not every Audacity command can be plugged into a "chain," but speed change just so happens to be one of the lucky ones.
Good luck with your listening,
Lifehacker
P.S. — We truly do appreciate the smiling coincidence of devising an automation process for the preeminent author of robotic-based fiction.
