According to AppleInsider, Apple snuck in two new bitrate options into iTunes 10.6 for users who sync their iTunes library to their iPhone or iPad. Most audio tracks are encoded at 256 kbps if they're bought from the iTunes Store, and now you can keep that quality when you send your files to your iOS device.
Starting with iTunes 10.6, users can choose to sync their tracks at 256 kbps, 192 kbps or 128 kbps. This new setting gives users the flexibility to select the right encoding to match the storage of their device and their preferred audio quality. Audiophiles with a 64 GB device won't have to sacrifice audio quality, while less discerning users with 16 GB of space can choose to sync a smaller, lower bitrate file.