(my setup: Acer Aspire One AO751h, Ubuntu Lucid 10.04.2 LTS)
A better way than changing the output balance is to use alsamixer or pavucontrol and mute one of the input channels. In alsamixer: F4 to change to recording, left/right to move to microphone, and z or c to mute one channel. In pavucontrol go to the "input devices" tab, unlock the channels, and mute one of the channels.
It seems the normal volume control uses one balance slider for all inputs and outputs together.
- Pulse Audio -- it still amazes me how a simple problem (enable audio on a PC) could be made so complicated and unusable;
- Skype for Linux -- a real disgrace that a company of the might and power of Skype could let us down so badly: I just wish they had the decency of release the software open source, so we could fix it ourselves!