First of all, thank you for your patience in waiting for this response-- many apologies for the delay!
To answer your question, the new Campbell releases through iTunes do in fact have a bitrate of 256 kbps. (I will check with Martin re: his previous response to see what led him to conclude that the new lectures are at 128 kbit/s, but can assure you that it is 256.)
We've made arrangements with iTunes to offer the entirety of the new lecture series with their iTunes Plus designation. Not only does iTunes Plus format feature the 256 kbps bitrate (as opposed to the formerly standard iTunes bitrate of 128 kbps), but iTunes Plus files are also DRM-free.
(DRM stands for Digital Rights Management, and when audio files include DRM encoding, that means they are limited in the number of machines they can be played on/transferred to. DRM-encoded tracks have been a sore point among digital music consumers since the inception of iTunes, and Apple has finally capitulated to industry demand by offering DRM-free tracks. So, once purchased, you can transfer/copy/listen to your Campbell lecture tracks anywhere, as much as you want-- this wouldn't have been the case with iTunes just a couple years ago.)
Here is a cut-and-paste from the Apple site describing iTunes Plus:
For more on this topic, you can read this article on the Apple site from May 2007, when iTunes Plus was first introduced. Back then, they imagined offering iTunes Plus tracks for $1.29 as opposed to the standard tracks for $0.99, but since then, they've lowered the price to $0.99 as well. In fact, iTunes Plus is becoming the new standard across iTunes, and Apple is in the process of phasing out the old standard so that everything will be iTunes Plus across the board:iTunes Plus music refers to songs and music videos available in our highest-quality 256 kbps AAC encoding (twice the current bit rate of 128 kbps), and without digital rights management (DRM). There are no burn limits and iTunes Plus music will play on all iPods, Mac or Windows computers, Apple TVs, and many other digital music players.
http://www.apple.com/pr/library/2007/05 ... splus.html
That's probably more information than you wanted, but I thought it might be helpful to have all of this info in one place.
Finally, thank you for your support for and enthusiasm for the lectures!
Please let us know if you have any more questions, and I promise to answer in a more timely fashion next time :-)
-Phil