Pseudo-Stereo Effect

Pseudo-stereo audio processing techniques generate two stereo channels from a single mono one to create a wider spatial impression and an illusion of a multi-directional audible perspective. Moreover, pseudo-stereo can be used as a creative audio manipulation tool. However, we can separate two things when discussing the stereo signal.

True Stereo 

The stereo signal consists of two related channels, with correlated material in the left and right outputs. For example, I use two-spaced-apart microphones 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 for the other, including adding a slight delay to one side, adding a chorus to one side, etc. For example, you could mix a mono guitar amp into 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

You can also apply this technique in several ways; we could mention at least two of them. The "Sum/Difference" method consists of a single central main speaker or cluster 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 on the 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

In most cases, the single-point speaker system will 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, unlocalized 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 use side-to-side panning for 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 EQs

There are also ways of achieving the "pseudo-stereo" effect by applying specific equalizer software plugins in the DAWs. The idea is to use a parametric EQ with 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. When the 2 channels add up to make a mono signal again, they produce a profound stereo effect. In addition, this deals with unwanted phasing and chorusing.