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I noticed I've ripped two different Arlo Guthrie CDs that I own ("Alice's Restaurant", and "The Best of Arlo Guthrie"). Rips probably done with different programs, years apart.

Each had "Alice's Restaurant Massacree" on the CD, each was ripped to mp3.

The two mp3 files are reportedly the same "kind" (Audio file with ID3 version 2.3.0, contains:MPEG ADTS, layer III, v1, 128 kbps, 44.1 kHz, JntStereo), and nearly the same length (18:36 for the larger one, 18:33 for the smaller one), but the older/larger one is 80% larger than the other.

Any ideas why?

The file info is:

sf: ls -l /alic

-rw-r--r--@ 1 sieler  staff  31536096 Apr  6  2008 alices_restaurant/alices_restaurant_massacree.mp3
-rw-r--r--  1 sieler  staff  17342000 Dec 29 22:37 the_best_of_arlo_guthrie/alices_restaurant_massacree.mp3

sf: file /ali

alices_restaurant/alices_restaurant_massacree.mp3:        Audio file with ID3 version 2.3.0, contains:MPEG ADTS, layer III, v1, 128 kbps, 44.1 kHz, JntStereo
the_best_of_arlo_guthrie/alices_restaurant_massacree.mp3: Audio file with ID3 version 2.3.0, contains:MPEG ADTS, layer III, v1, 128 kbps, 44.1 kHz, JntStereo

sf: ssaudio /ali

mp3 Duration:    18:36 :: alices_restaurant/alices_restaurant_massacree.mp3
mp3 Duration:    18:33 :: the_best_of_arlo_guthrie/alices_restaurant_massacree.mp3

ssaudio is a utility I wrote to peek at audio files of various format and try to find/report their duration information ... not all mp3 files contain such information. If anyone is interested in it (Linux, Mac, Windows), let me know.

(Oddly, macOS "Get Info" (and Quicktime app) both report the songs are 18:37 ... but I've dumped the files in hex, found the "TLEN" entry, and verified that my utility is correctly reporting that the lengths are slightly different.)

thanks!

Stan

Stan Sieler
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    Best guess: implementation of compression improved over the decades. Since compression decouples the file size from the audio length, you can always do it worse. – guidot Dec 30 '21 at 20:19
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    One may be fixed rate, the other variable. The only simple drag & drop app I have that shows that has vanished from the web. – Tetsujin Dec 31 '21 at 13:24
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    use mp3info with -xrv flags and it'll tell you if it's variable bitrate or not. The Audio: line will either give the bitrate such as 128 kbps, or it'll say Variable kbps. – nelgin Jan 02 '22 at 09:51

2 Answers2

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At constant 128kbps the music data shouldn't be more than 17,4MB, so if the file isn't corrupt in any way, the only reasonable explanation is that the larger file has lots of metadata in it, possibly album art. Lookup ID3v2 for more info.

tallberg
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MP3 is a compressed file format. I'm probably not telling you anything you don't know, but for the sake of completeness it essentially uses a codec to compress a music file, typically removing all frequencies which are beyond the range of normal hearing. Some codecs achieve this with better results than others. For example, one of the "artifacts" of a poorly compressed MP3 is a swishing sound when cymbals are hit by the drummer.

As such, one codec may have used better optimization or cut out more of the frequency range than the other, which would result in differing file sizes. The only way to know which is better is to actually play and compare them. You could also use one of the many Frequency Analysis applications out there to see if one has a wider frequency range than the other.

Johnny Bones
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