# Why would an MP3 sound file drop in bit rate when transferred via Dropbox? **URL:** \ **Category:** Factual Questions\ **Created:** [May 22, 2016, 11:35pm UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418 "2016-05-22T23:35:12Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Infovore](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/infovore/32/420_2.png) [@Infovore](https://boards.straightdope.com/u/Infovore)\ **Post date:** [May 22, 2016, 11:35pm UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/1 "2016-05-22T23:35:12Z")
Any audio gurus out there? I have an audiobook project I’m working on, and I keep having trouble with ACX’s requirement that the files be at least 192kbps. When the engineer sends them to me (by posting them in a Dropbox directory) he told me the first batch was encoded at 192kbps, but when I tried to upload them, ACX said they weren’t high enough. I looked at them in iTunes and they showed up as 112-114. He sent me a new set of files encoded at 256, but these show up as 177-181. (I tried uploading a chapter to ACX before I put them in iTunes, in case iTunes was doing some kind of compression I wasn’t aware of). He can’t figure out what’s going on–they’re fine on his end, and compressed on mine. I tried uploading them from both my Mac and my PC, and got the same problem. The file size on his end and my end are the same (for example, Chapter 1 is 10.9 MB for us both). Originally I downloaded the files as one big .zip file, but I tried downloading individual files and get the same result. Anybody have any idea what might be going on? ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [May 23, 2016, 12:26am UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/2 "2016-05-23T00:26:49Z")
maybe it’s confused by variable bit rate/average bit rate-encoded files? ---
**Author:** ![davidm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/davidm/32/225_2.png) [@davidm](https://boards.straightdope.com/u/davidm)\ **Post date:** [May 23, 2016, 12:30am UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/3 "2016-05-23T00:30:31Z")
Does the bit rate change when they’re in a zip file? If not, then have him zip them before uploading (you can zip individual files). That said, I’m skeptical that Dropbox is changing file contents. ---
**Author:** ![Infovore](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/infovore/32/420_2.png) [@Infovore](https://boards.straightdope.com/u/Infovore)\ **Post date:** [May 23, 2016, 12:30am UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/4 "2016-05-23T00:30:32Z")
> [@jz78817](#): > > maybe it’s confused by variable bit rate/average bit rate-encoded files? Can you explain that in English, please? 😃 I’m pretty much a n00b when it comes to this sort of thing. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [May 23, 2016, 12:35am UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/5 "2016-05-23T00:35:23Z")
If the files really did get reencoded to a different bit rate, the size of the file would be different. Check the size of your files and compare them with the size of the sender’s files. –Mark ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [May 23, 2016, 1:38am UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/6 "2016-05-23T01:38:51Z")
> [@Infovore](#): > > Can you explain that in English, please? 😃 > > I’m pretty much a n00b when it comes to this sort of thing. there are a few different ways to encode an MP3 file. “constant bit rate” means just that, it uses a constant number of bits per second. So, an MP3 encoded at 192 kb/s constant-bit-rate will use 192,000 bits for every second of music, period. “variable bit rate” means the encoder will use a different number of bits per second depending on what’s required to meet the desired sound quality. “average bit rate” means the encoder will target an average bit rate, but may go higher or lower depending on how complex the segment of music is. some older tools for working with MP3 files can get confused with files using VBR or ABR. if they look at a particular “frame” within the file, they might see a lower number than desired. ---
**Author:** ![Wolf333](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolf333/32/3460_2.png) [@Wolf333](https://boards.straightdope.com/u/Wolf333)\ **Post date:** [May 23, 2016, 2:02am UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/7 "2016-05-23T02:02:35Z")
From ACX: be a 192kbps or higher MP3, **Constant Bit Rate** (CBR) at 44.1 kHz ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [May 23, 2016, 3:00am UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/8 "2016-05-23T03:00:04Z")
Assuming you both have access to gmail have him send you a chunk that’s 25 megs or less so you can use gmail for the transfer and test. I would say chances are 99.99% it’s not dropbox but how the different programs are reading and writing bit rates. Have you tried a different media play or assembly program to see what it says? What does simply right clicking on the file “properties” then “details” in windows explorer say about the file? ---
**Author:** ![Infovore](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/infovore/32/420_2.png) [@Infovore](https://boards.straightdope.com/u/Infovore)\ **Post date:** [May 23, 2016, 3:06am UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/9 "2016-05-23T03:06:26Z")
> [@Wolf333](#): > > From ACX: > > be a 192kbps or higher MP3, **Constant Bit Rate** (CBR) at 44.1 kHz Yes, exactly. The 44.1 part is fine. The 192 is where we’re having the problems. ---
**Author:** ![Infovore](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/infovore/32/420_2.png) [@Infovore](https://boards.straightdope.com/u/Infovore)\ **Post date:** [May 23, 2016, 3:07am UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/10 "2016-05-23T03:07:30Z")
> [@markn\_1](#): > > If the files really did get reencoded to a different bit rate, the size of the file would be different. Check the size of your files and compare them with the size of the sender’s files. > > –Mark We did. As I said, we tested one chapter - it shows as 10.9 MB on both his system and mine, but his says it’s 256 and mine (and ACX) say it’s 177. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [May 23, 2016, 3:23am UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/11 "2016-05-23T03:23:53Z")
then it’s VBR/ABR and ACX is choking on it. ---
**Author:** ![Infovore](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/infovore/32/420_2.png) [@Infovore](https://boards.straightdope.com/u/Infovore)\ **Post date:** [May 23, 2016, 3:48am UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/12 "2016-05-23T03:48:24Z")
> [@jz78817](#): > > then it’s VBR/ABR and ACX is choking on it. Does that mean my system is choking on it too? Because as I said, when I import it into iTunes (the only way I know to be able to look at the bit rate), it shows up as 177, not 256. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [May 23, 2016, 4:22am UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/13 "2016-05-23T04:22:13Z")
> [@Infovore](#): > > Does that mean my system is choking on it too? Because as I said, when I import it into iTunes (the only way I know to be able to look at the bit rate), it shows up as 177, not 256. What does simply right clicking on the file “properties” then “details” in windows explorer say about the file? ---
**Author:** ![Infovore](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/infovore/32/420_2.png) [@Infovore](https://boards.straightdope.com/u/Infovore)\ **Post date:** [May 23, 2016, 6:23am UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/14 "2016-05-23T06:23:54Z")
> [@astro](#): > > What does simply right clicking on the file “properties” then “details” in windows explorer say about the file? Well, it didn’t work on the Mac (which is what I’m primarily using). I will check it on the PC. However, the engineer sent me some new files (encoded at 320kbps this time) and, go figure, they didn’t change at all. I got them at 320, and ACX accepted them, so I think I’m good to go. ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [May 23, 2016, 2:51pm UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/15 "2016-05-23T14:51:44Z")
Whatever transfer app you’re using, email or FTP etc., it may be detecting the type of file and re-encoding it to save bandwidth (without asking first). Similar to how MS Outlook will ask for a ‘quality’ setting when you attach picture files (.jpg, .bmp etc.) to email messages. A simple way to check would be to change the file’s three letter extension before sending it. Instead of _soundfile.mp3_ change it to _soundfile. **old** _ then the app won’t recognize it (you have to change it back before trying to open it)… ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [May 23, 2016, 3:17pm UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/16 "2016-05-23T15:17:03Z")
> [@Infovore](#): > > Well, it didn’t work on the Mac (which is what I’m primarily using)… The equivalent for Mac is right click \> Get Info. ---
**Author:** ![Infovore](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/infovore/32/420_2.png) [@Infovore](https://boards.straightdope.com/u/Infovore)\ **Post date:** [May 23, 2016, 3:25pm UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/17 "2016-05-23T15:25:05Z")
> [@Hail\_Ants](#): > > Whatever transfer app you’re using, email or FTP etc., it may be detecting the type of file and re-encoding it to save bandwidth (without asking first). Similar to how MS Outlook will ask for a ‘quality’ setting when you attach picture files (.jpg, .bmp etc.) to email messages. > > A simple way to check would be to change the file’s three letter extension before sending it. Instead of _soundfile.mp3_ change it to _soundfile. **old** _ then the app won’t recognize it (you have to change it back before trying to open it)… Ah, good idea! Next time I have to try this, I’ll do that and see if it works. ---
**Author:** ![Infovore](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/infovore/32/420_2.png) [@Infovore](https://boards.straightdope.com/u/Infovore)\ **Post date:** [May 23, 2016, 3:26pm UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/18 "2016-05-23T15:26:12Z")
> [@pulykamell](#): > > The equivalent for Mac is right click \> Get Info. I know that. But the info that shows up doesn’t include the bit rate. It includes the 44.1K part, but not the 192. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [May 23, 2016, 3:32pm UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/19 "2016-05-23T15:32:37Z")
> [@Infovore](#): > > We did. As I said, we tested one chapter - it shows as 10.9 MB on both his system and mine, but his says it’s 256 and mine (and ACX) say it’s 177. If the file size is the same, then obviously it’s not being re-encoded. I’m guessing the file is encoded as VBR (variable bit rate); when you use VBR, you specify the maximum and minimum bit rate, and the encoder varies the actual bit rate as needed. I’m guessing one software/OS is reporting the maximum bit rate (256 is typical) and the other is reporting the average actual bit rate (177). ---
**Author:** ![control-z](https://avatars.discourse-cdn.com/v4/letter/c/eada6e/32.png) [@control-z](https://boards.straightdope.com/u/control-z)\ **Post date:** [May 23, 2016, 8:12pm UTC](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418/20 "2016-05-23T20:12:26Z")
> [@scr4](#): > > If the file size is the same, then obviously it’s not being re-encoded. I’m guessing the file is encoded as VBR (variable bit rate); when you use VBR, you specify the maximum and minimum bit rate, and the encoder varies the actual bit rate as needed. I’m guessing one software/OS is reporting the maximum bit rate (256 is typical) and the other is reporting the average actual bit rate (177). I think this is the correct answer. If the file size is the same then it’s likely the same file. And I don’t think Dropbox is messing with it, re-encoding someone’s file would pretty much defeat the purpose of cloud storage. Have the author ensure it’s a constant bitrate file because ACX specifically asks for that. [Next page](https://boards.straightdope.com/t/why-would-an-mp3-sound-file-drop-in-bit-rate-when-transferred-via-dropbox/755418.md?page=2)