Hi all I know this is not the ideal place to ask a question about Android--but I hope someone here can help confirm my suspicions. I wanted to create some circuit tools using the 1/8" stereo output + line input jack on my android phone (a droid razr). To start with, I've got a simple signal generator (built with PdDroidParty)--and what I found is that there is a high-pass filter on the output. It is mostly unsurprising, but what *kind* of high-pass filter is it? If it was just a RC impedance on the output, I could compensate for that. However, it seems likely that there's a high-pass filter in the software, or somewhere else. When I drive it to clipping with a combination of sine tone and dc offset, the noise characteristic is weird. The pitch of the distorted tone goes down, and there's a very steep transition between the undistorted and distorted tone. The distorted tone is also much louder. I'm typically testing with a tone at about 1kHz, but I've been sweeping through a lot of frequencies to see what happens. The symptom is the same whether it's played through the speaker or a set of headphones. It's got to be a software filter, DAC hardware, or output amplifier circuit. If I could identify that, it would help me figure out whether this project is feasible or not. I'd like to make hardware that plugs in to the 1/8" jack to create: 1. signal generator 2. RLC meter ... up to ... linear/non-linear systems identification tools audio spectrum analyzer audio oscilloscope USB hardware is mostly out of my league--and for the effort required, there's no guarantee of success. Small steps, first. Chuck