Skype hack for Mac: restore Auto Gain Control and Echo Cancellation

[detn8r]

Kevin C. from jkOnTheRun writes:

The rumors are true; I'm now addicted to reading through Skype forums. After last week's nugget on how to enable VGA res on an integrated iSight for Skype video calls, I decided to tackle another issue. Ever since I started Skyping on a Mac, I've had a terrible problem that basically will not allow me to use the integrated microphone for Skype calls. The issue revolves around the input levels for the mic: on a Skype call, the levels would quickly jump up on their own. The result: a constant feedback echo or loop on the call because the higher mic levels pick up the audio from the speakers; the conversation just cycles until I mute the mic. After poring through the forums, it turns out I wasn't alone. Even better yet, I found a potential fix and got it to work after a little more XML tweaking....

It appears that the root cause of the problem is directly related to audio features in Skype: Automatic Gain Control and Echo Cancellation. The main issue is due to the AGC, since that's the mechanism that's overriding the mic levels in the system sound settings. The problem is: these two functions are nowhere to be found in the Skype GUI! I've checked both versions 2.5 and the 2.6 beta for Mac, but they somehow got overlooked.

Luckily, even though the configuration options aren't in the GUI, the functionality is still there if you know how to use it. First up: close your Skype application. Next, you'll need to find your "shared.xml" file for Skype, which typically resides at /Users/Your Account/Library/Application Support/Skype. I used TextEdit to open the XML file and went to the "VoiceEng" tags. Here's how this section would typically appear:

The number in the MicVolume tag will vary and will be a number between 0 (muted) and 255 (highest input level). Even though there's no reference here to either the Automatic Gain Control or the Echo Cancellation, both are apparently on by default, which is causing my issue. The fix is to add these tags for both, along with an element value of zero:

Once you've made these changes and saved the .xml file, you're good to go with Skype again. At this point, you can fully control the microphone input levels through the System Preferences, Sound system settings. Why these functions were dropped from the Skype GUI is beyond me, but I'm thrilled that I don't have to use my USB headset for each and every Skype call. As info: this fix was originally devised for Windows Skype clients, so if you're running the Windows version and don't see these two configuration options, this should work for you as well.