SoListenerDopplerElement(3) on Linux
The text 151ade583b32, as Debian 8 (Jessie) shipped it.
The SoListenerDopplerElement holds the doppler velocity and factor of the current listener. The dopplerVelocity and dopplerFactor is set by SoListener nodes during audio rendering. The SoListenerDopplerElement is used when the SoVRMLSound nodes render themselves.