Can someone help me understand the process FMOD uses to upmix a stereo sound into surround via the “Stereo In: Distributed” option on the surround panner? How are the two channels distributed throughout a 3D sound field? What effect would it have on a music track for example?
The Stereo In: Distributed mode distributes the signal from both channels to all the channels weighted according to their original channels and the Surround Extent and Surround Direction properties of the panner.
By default, the signal from the left channel of the input will be distributed such that it’s loudest in the left channel of the output, but can be heard in every channel other than the right and LFE channels, and the signal from the right channel of the input will be distributed such that that it’s loudest in the right channel of the output, but can be heard in every channel other than the left and LFE channels. (Stereo In: Distributed mode only distributes the signal to the LFE channel if LFE is toggled on.)
Changing the direction and extent properties of the panner (by dragging the white dot in the center of the panner circle) modifies this behavior by weighting the distribution towards whichever speakers are closest to the dot.
Music in stereo channel format is affected in the same way as other kinds of input in stereo channel format.
So, just to clarify, if we go from stereo to 5.1 using Stereo In : Distributed and do not change the direction or extent: the left channel is weighted heavily on the FL and ultimately sent to the FL, LS & RS and the right is weighted heavily on FR is sent to FR, RS, LS?
That’s correct, more or less. You’ll also hear both left and right channels of the source being distributed to the center channel of the output. You can demonstrate the distribution clearly by adding an FMOD channelmix effect to the track and setting either the left or right channel to -oo dB, or by using a stereo source audio file that only has an audible signal in one channel.
That makes sense! Thanks for your time!