Thanks for the replies. I ended up using: m_pEndpointVolume->QueryHardwareSupport(&dwHardwareCapabilities); if(MicrophoneMute == lSetting) { if(dwHardwareCapabilities & ENDPOINT_HARDWARE_SUPPORT_MUTE) Which was missing from the earlier SDK docs, but is there now. Thanks again. Andy ****************** WDMAUDIODEV addresses: Post message: mailto:wdmaudiodev@xxxxxxxxxxxxx Subscribe: mailto:wdmaudiodev-request@xxxxxxxxxxxxx?subject=subscribe Unsubscribe: mailto:wdmaudiodev-request@xxxxxxxxxxxxx?subject=unsubscribe Moderator: mailto:wdmaudiodev-moderators@xxxxxxxxxxxxx URL to WDMAUDIODEV page: http://www.wdmaudiodev.com/