Originally Posted by musiciscool
[...] Why shouldn't they allow the line in to be stereo? Is it to difficult to engineer?
Because then you'd have to have a custom miniplug connector. Right now it has four connections: ground, headphone out L and R, and mono mic input. This is a standard configuration and a common part. They'd have to otherwise build something proprietary, or have a second connection. And really, how much demand will there be for it? And even more so, how much demand for pro quality and the increased price? I mean, my Cirrus Logic stock would thank you, but it would be something that wouldn't be used by 99.999% of the iPhone or iPad users. If it cost Apple $5 more to put in, and they sell 10M iPhones while maintaining their last-model pricing (as they are prone to do), they'd be giving up $50M in revenue so a couple Gearslutz can make some stereo line-in recordings.
Better to let a auxiliary device handle it through the digi i/o. Alesis, Apogee, Mackie, L6, various other companies all make devices that integrate with the dock connector.
What would have been interesting (and probably more technologically viable), but even more esoteric, would be the optical i/o that's embedded in the MacBook Pro mini plug jacks.
But using my iPhone for quick line-in two track recordings is handy. I have a Microtrack that really doesn't get used all that often anymore unless I need to spot record acoustically with a mic.