iTunes displays two quantitative measures for the "quality" of the encoded audio for an audiobook, the bit rate and the sample rate. The bit rate is the best pragmatic measure of quality, it basically describes the amount of bytes it takes to record a second (or whatever) of audio. More bytes = higher quality, all other things being equal (which they never are, but let's not get complicated). Skip sample rate for now.
Audible has multiple formats, 2-4 and "Enhanced". (Format 1 was discontinued, it dated to when 64 megabytes would be a high capacity player.) Apple only sells audiobooks encoded in one format, recognizing that (most) people don't want to have to make decisions about which format to choose.
In terms of the quantitative measures of quality, here are the specifics of the three highest quality formats between both Apple and Audible:
Vendor | Format | Bit Rate | Sample Rate
~~~~~~ | ~~~~~~~~~ | ~~~~~~~~ | ~~~~~~~~~~
Audible | "Format 4" | 32 kbps | 22.050 kHz
Apple | AAC (.m4b) | 32 kbps | 24.000 kHz
Audible | "Enhanced" | 64 kbps | 22.050 kHz
As you can see from the differing sample rates, while Audible is indeed the supplier of Apple's audiobook titles, they don't supply the audio file directly. Apple's audiobooks have a different sample rate (which probably doesn't affect quality perceptibly), and they use a different encoding format.
In terms of more subjective measures of quality, the first two formats in the list are roughly comparable, and they are both "more than good enough." But if you have hard drive space and capacity on your listening device, Audible Enhanced is noticeably more crisp and clear, especially with books that have musical passages (e.g., mood music in between chapters). Enhanced format is relatively new, within the last year or so (my oldest Enhanced audiobook is dated 3/9/2009).
Audible has multiple formats, 2-4 and "Enhanced". (Format 1 was discontinued, it dated to when 64 megabytes would be a high capacity player.) Apple only sells audiobooks encoded in one format, recognizing that (most) people don't want to have to make decisions about which format to choose.
In terms of the quantitative measures of quality, here are the specifics of the three highest quality formats between both Apple and Audible:
Vendor | Format | Bit Rate | Sample Rate
~~~~~~ | ~~~~~~~~~ | ~~~~~~~~ | ~~~~~~~~~~
Audible | "Format 4" | 32 kbps | 22.050 kHz
Apple | AAC (.m4b) | 32 kbps | 24.000 kHz
Audible | "Enhanced" | 64 kbps | 22.050 kHz
As you can see from the differing sample rates, while Audible is indeed the supplier of Apple's audiobook titles, they don't supply the audio file directly. Apple's audiobooks have a different sample rate (which probably doesn't affect quality perceptibly), and they use a different encoding format.
In terms of more subjective measures of quality, the first two formats in the list are roughly comparable, and they are both "more than good enough." But if you have hard drive space and capacity on your listening device, Audible Enhanced is noticeably more crisp and clear, especially with books that have musical passages (e.g., mood music in between chapters). Enhanced format is relatively new, within the last year or so (my oldest Enhanced audiobook is dated 3/9/2009).
The iPod and iPhone can handle files that contain approximately 2 billion audio samples or less. This translates into roughly
- 27 hours for Audiobook Builder's Low Quality preset (22.05 kHz)
- 18 hours for its Normal Quality preset (32 kHz) and
- 13 hours for its High Quality preset (44.1 kHz).
The lower the audio sample rate the longer your parts can be. It's possible to reach a maximum part length of 74 hours by selecting the Custom... Quality option and choosing an 8 kHz sample rate. Files that exceed the 2 billion sample limit will not play properly on the iPod or iPhone.
No comments:
Post a Comment
Note: Only a member of this blog may post a comment.