Are there any Android devices available that support multi-channel (stereo) recording via line-in?
With the devices I tested (Nexus 4, HTC Buzz, Motorola Xoom ..), it is possible to set AudioFormat.CHANNEL_IN_STEREO, but I only receive one active channel.
Is this a gerneral limitation of Android due to licensing issues or is this depending on the manufacturer/hardware, i.e. there is only one A/D converter for input or some such?
Any experiences, thoughts or ideas on this topic?
Are there any Android devices available that support multi-channel (stereo) recording via line-in?
Concerning most smartphones and tablets factory-equipped with Android there is an unpleasant answer: No.
Why not? Because these devices (and BTW also all iPhones) use the 4pin TRRS-3.5mm-plug to connect headphones and/or microphone to the device. The four pins are used for T) left speaker, R1) right speaker, R2) ground for speaker and microphone, and finally S) monophonic microphone.
UPDATE: When I added in Dec 2013 that "the invention of the TRRRS (I would suggest to call it "T3RS") plug would solve the problem" I couldn't know that Sony was already working on that and presented the "STM-10" stereo microphone with exactly that T3RS-plug in Feb 2014.
Is this a gerneral limitation
Yes, but simply due to the hardware audio plug, not due to licensing.
In 2014 there came very few Android smartphones that have the T3RS-plug with external stereo input: Xperia Z2, Z2 tablet, Z3
As a side note, the gain of the input amplifier is adjusted to microphone output level and not to line level (e.g. of a CD-player).
Olimex OLinuXino A10S https://www.olimex.com/Products/OLinuXino/A10S/ has a LINE_IN connector. I haven't found out how to access it yet, but it is there!
来源：https://stackoverflow.com/questions/14812579/line-stereo-2-channel-recording