Vista Volume Control is a command-line application to control the various volume-levels (master and individual levels) of capture and render devices. Additionaly, it can be used to turn the microphone boost on and of (this has only been tested on Audigy 2 cards, but has some internal logic to work on other devices - if it does not work, drop me a mail).
General usage: VolumeControl.exe capt|rend count|(def|INDEX OPERATION [OPERATION ...]) [capt|rend ...]: capt|rend: operate on capture or render endpoint count : display corresponding endpoint count def : operate on default capture/render endpoint INDEX : device index, between 0 and endpoint count OPERATION: one of the following: stepup : master volume step up stepdown : master volume step down volumedb FLOATVALUE : set master volume level to FLOATVALUE dB volumescalar FLOATVALUE: set master volume level to FLOATVALUE : (between 0.0 and 1.0) mute : mute endpoint unmute : unmute endpoint togglemute : toggle mute status of endpoint displayinfo : display information on endpoint : (MIN/MAX dB values, current volume, etc.) traversedevicepath : display device graph of endpoint : (only the input multiplexer part) OPERATIONs specific to render endpoints: pathcount : display available device paths level DEVPATH LEVELOP : operate on individual volume level : DEVPATH is the path id, between 0 and path count LEVELOP is one of the following: volumedb FLOATVALUE : set volume level to FLOATVALUE dB volumescalar FLOATVALUE: set volume level to FLOATVALUE : (between 0.0 and 1.0) mute : mute volume level unmute : unmute volume level displayinfo : display information on volume level : (MIN/MAX dB values, current volume, etc.) OPERATIONs specific to capture endpoints: enablemicboost : enable microphone boost (if present) disablemicboost : disable microphone boost (if present) Multiple operations on endpoints can be combined, operations on volume levels can not ("level DEVPATH" is needed in front of each level operation).