Why would this MP3 play slowly in Audacity?

April 19, 2009 9:29 AM

Why would an MP3 play at a significantly different speeds in Audacity and Windows media player, respectively? Specifically, Audacity is playing the file waaay to slow.

When I listen to a particular, MP3, specifically Crush Mode, by the Glitch Mob, it plays at apparently normal speed, with a running time of 40:44. However, When I open it in Audacity, it plays much, much s-l-o-w-e-r, and at a running time of 55:57, and the sound is pitched way down. Almost like playing a 45 on 33, for those of you old enough to remember vinyl. I've never had this happen before, and wonder what is so magical about this particular mp3 that is seeming to baffle Audacity.

Anyone had this happen before? And what might I do to get Audacity to play the file at the correct speed?

posted by chocolate_butch to technology (4 comments total)

It sounds like a 48KHz vs 44.1KHz issue with the file, and Audacity getting confused.
posted by onya at 9:47 AM on April 19

This is not an unknown problem, as a quick google search shows. The suggestions in many of those links say to check the sampling speed settings and adjust those.
posted by hippybear at 9:49 AM on April 19

My guess is that your mp3 is encoded in a non-standard sample rate + bitrate using LAME (possibly with --freeformat), and Audacity doesn't know what to do with it. Not all encoders/decoders are equally capable.

If you don't want to lose any quality, try using LAME's --decode function to convert it to a WAV file before importing. You can also resample it to something standard (22.05, 44.1, 48) with LAME if necessary.
posted by cj_ at 1:05 PM on April 19

This has happened to me a few times with podcasts I was trying to snip some segments out of via Audacity. I don't know if it's just encoding, because I've never seen it happen to more than one episode of any particular podcast, and I'd assume that a given podcast is fairly consistent in how it's encoded.

Anyway. Here's how I address it: I know the 'correct' length of the file via iTunes. I know the 'incorrect' length in Audacity when I load it. I treat this as a ratio and do a rough estimate, then use the "Change Speed" effect in Audacity to make the file the correct length (and hence pitch) again. If my estimate was off by any amount, I hit undo and re-execute Change Speed using a slightly different percentage, until I hit it right on the nose.
posted by sesquipedalia at 11:03 PM on April 19