Here's a short video made with my second attempt (or second finished attempt, out of many) to kill the Alpha 77's extremely noisy auto gain audio problems:http://youtu.be/AgFU2nV2A4c
I've been trying to rig up some way to record to the camera (after all, it has 48 kHz sound which is better than CD quality) using either the onboard mic, or the stereo input. There is a real issue with the onboard in quiet situations, it simply boosts silence to the point that a loud white noise hiss dominates, which then ducks out in an ugly way if speech or music comes in. Using external mics of different types, it's not as bad, but still bad enough to be unusable for serious amateur purposes.
If anyone has a solution, I'd love to know. I have tried: external Audio Technica Stereo Shotgun mic - camera does not seem to like the stereo and records left side only, but will try to buy another cable. Built-in mic - unacceptable auto gain changes and quiet passage noise. Mackie Onyx preamp with two AKG C2000B studio mics - results vary, if camera is switched on with this plugged in, terrible auto gain with hum and hiss; if the rig is plugged in during a take which starts with the internal mics, sometimes the external will take over and have much cleaner sound and apparently disable auto gain, but sometimes the internal mic will not be defeated. Small Sony ECM-717 tieclip stereo mic made for MiniDisk system - so far, the best sound, less volatile auto gain and lower quiet passage hiss.
Sony MUST issue new firmware for the A77 (and future NEX, or other cameras) to enable either one fixed gain audio level, to disable auto gain when using external mics, or to have controllable gain (Nikon has auto plus three manual levels, Canon has a 64-step manual volume option with on-screen dB meter).