Below is an example of a speaker spreader system and a discussion of how it is built up from individual modules.
A speaker spreader widens the image of a stereo signal. To accomplish this, some mathematical modules are used.
First, a Deinterleaver module must be used to separate the channels. The separate left and right channels are then fed into a SumDiff module. The SumDiff module takes two inputs and outputs both half their sum and half their difference, as shown below.
If Inputs 1 and 2 are the left and right channels, then Outputs 1 and 2 have special properties. Output 1 (the sum) is the portion of the signal that forms the center image, while Output 2 (the difference) is the stereo or wide portion. By boosting or reducing these, stereo image width increases and decreases. The Scaler modules that follow will be used to control the system in real-time (hence the smoothing).
After scaling, the signals are then passed through another SumDiff module to help us return to proper Left and Right channels, shown below.
Mathematically, the signals are now half the level they started out as, so after the Interleaver module recombines the channels, a Scaler module applies a linear gain of 2.
The Multiplexor module is used to show the difference the speaker spreader makes. By selecting and deselecting its index, the module toggles between the spreader and the unprocessed signal in real-time. Increasing the gain on the difference channel should spread the sound image.