Why are iTunes audiobooks stereo?

[Wowfunhappy]

I am dumbfounded. I can barely believe my own eyes.

For many years now, I have thought that encoding audiobooks in stereo—normal audiobooks, without background music or sound effects or anything like that—was universally stupid.

A narrated book, I'd thought, was a single person's voice. There was zero reason to use stereo, because both channels would be exactly the same. It is unclean at best and an (admittedly-minor) waste of space at worst.

But I've just discovered that every Audiobook I've ever bought from iTunes was in fact encoded in stereo.

Since I find it hard to believe that Apple, of all people, does not know how to properly encode things... why would they do this? What advantage does it serve? When I rip books-on-CD, should I be encoding them in stereo as well? I generally try to follow Apple specs when I encode stuff.

[mariush]

Most codecs have some kind of joint stereo mode or mechanism where they split audio into what's the same on both channels and a separate stream that can be encoded with fewer bits. There may be just a tiny percentage of total bits used to create the stereo effect.

Or maybe both channels have exactly the same content, in which case you're practically wasting no bits for second channel, it's just some flags in the audio header.

At least with FLAC, I've experimented...made a mono track and compressed it, then doubled the channel to produce a stereo file and the FLAC encoding had the same size.
Another reason for stereo could be compatibility - in my particular case, my Sansa Clip portable player can't play mono flac files, but a flac file with that channel duplicated and marked as stereo plays just fine.
Anyway, in the end voice can be compressed quite well, maybe 60-90 kbps are more than enough for voice in stereo (if compressed in aac) ... so it's not like you're downloading huge amounts of data.

[Sharc]

...A narrated book is a single person's voice. There is zero reason to use stereo, because both channels should be exactly the same..
Not strictly. There is always a natural environment which causes multi-path propagation with reflections (reverberations) which is perceived slightly different by the 2 ears. Stereo will therefore sound more natural than a pure single channel even when the source is one speaker only. It has nothing to do with intelligibility though.

[Ghitulescu]

I believe it's better for their HW/SW combination. Has little to do with intelligibility, two personal ears and stuff...
The comparison with CD is wrong. The CD was already stereo, and the "monoing" it would be immediately perceived as a lack of quality.

[StainlessS]

At least one version of Power DVD cannot play mono properly and sounds like Donald Duck (think some players dont like it too, VLC [some versions] dont like audioless clip).

[Wowfunhappy]

I believe it's better for their HW/SW combination. Has little to do with intelligibility, two personal ears and stuff...
The comparison with CD is wrong. The CD was already stereo, and the "monoing" it would be immediately perceived as a lack of quality.
Sorry, to be clear—I was referring to Books-on-CD. I've edited the first post to reflect this. I know that all CD's are technically stereo, but I had thought that for a single-voice recording the channels would be exactly the same.

Not strictly. There is always a natural environment which causes multi-path propagation with reflections (reverberations) which is perceived slightly different by the 2 ears. Stereo will therefore sound more natural than a pure single channel even when the source is one speaker only. It has nothing to do with intelligibility though.

This is what I really wanted to know, thank you. So there are possible audio quality advantages to using stereo, even for a single voice recording.

Is there any way I can see whether the stereo in my audiobooks is actually being used? I opened up a couple of books in audacity and at least to my eyes, the waveforms look like they are exact copies of one another.

[StainlessS]

Dont know of anything in Audacity, but Steinberg WaveLab has something called Phase Scope,
Mono would produce a single vertical line in center, stereo spreads out horizontally as below

https://s20.postimg.org/jp88os0ot/Phase_Scope_zpsfuwvq70d.jpg (https://postimg.org/image/92efjcsjd/)

Perhaps something else also has Phase Scope

[Wowfunhappy]

Okay, so it looks like the left and right channels are in fact 100% identical, in every iTunes book I've tested. Which leaves me still very confused as to why Apple is doing this. :/

(To respond to a question I received in a PM—yes, iTunes audiobooks are DRM'd, but I used Requiem to losslessly strip out the encryption)

Is it possible to change the number of channels listed in the mp4 header? I recognize that there's no space disadvantage to having two identical channels, but I'd like the metadata to reflect reality.