Pseudo-stereo audio processing techniques generate two stereo channels from a single mono one, for the purpose of generating a wider spatial impression, while creating an illusion of multi-directional audible perspective. Moreover, you can use pseudo-stereo as a creative audio manipulation tool in itself. However, we can separate two different things when we talk about the stereo signal.
True Stereo
The stereo signal consists of two related channels, with correlated material in the left and right outputs. For example, using two microphones spaced apart to capture a signal.
Pseudo-stereo or simulated stereo
Pseudo-stereo is one of several different techniques for creating a two-channel output from a mono input. It utilizes processing for one channel and no processing on the other channel, including adding a slight delay to one side, adding chorus to one side, etc. For example, mixing a mono guitar amp to two channels with the left side dry (no effects) and the right side processed with a very short delay (a few milliseconds).
Methods for applying Pseudo-stereo
There are also several ways how you can apply this technique; we could mention at least two of them. The “Sum/Difference” method consists of a single central main speaker or cluster, essentially identical to what you would use as a mono system. This speaker gets the Left-plus-Right mono sum. A second speaker system consisting of two or more speakers along the side walls gets the Left-minus-Right difference signal. Thus, only the center speaker reproduces anything presented equally in Left and Right, a mono signal with a solid center image at every seat because a real loudspeaker is at that location.
Creating a spacious sound
The single point speaker system will in most cases have high speech intelligibility. Any signal presented in Left only or Right only will be reproduced by both the main central speaker and the side speakers. The side speakers design should provide a diffuse unlocalizable sound. This gives the sound a spacious room filling characteristic. There is no specific left or right localization. A left to center to right panning action will be reproduced as spacious – direct – spacious.
However many of today’s recordings don’t make strong use of side to side panning for the sake of imaging. They instead use the sides for spaciousness and effects. At the same time, the center is used for the main dominant instruments and voices. The Sum/Difference method is particularly suited to training videos. The talking head is always panned center and stereo spread is only used for the music bed and audience effects.
Using EQ’s
There are also ways of achieving the “pseudo-stereo” effect by applying certain equalizer software plugins in the DAW`s. The idea is to use a parametric EQ that has a separate control over its left and right channels. The whole point of this method is to periodically remove frequencies from one channel (left) while leaving them to play on the other channel (right). This means that whatever we remove from the right channel we leave on the left and vice versa.
In essence, when the 2 channels add up to make a mono signal again, they produce a really deep stereo effect. In addition, this deals with unwanted phasing and chorusing.
Additional Resources & Source Texts
http://www.csounds.com/journal/issue14/PseudoStereo.html?fbclid=IwAR3ADYI7NpISbl286y_q9TF4LcOB5gk1NF5i-jkjbFhxi77AYBAE3KEOvpk
