In mastering, the time given between each song is called the Spread. As much an art as the rest of the mastering process, often the spread between songs is not a set value of 2, 3 or 4 seconds. Many mastering engineers and producers prefer to use the spread to help define the overall feel or experience of a project by timing the spread to the tempo feel of the song that just ended and in some cases the song that’s about to begin. So, if the tempo of a song is 120 bpm, the spread would correspond with that tempo so that the down beat of the next song is in tempo with 120 bpm from the end of the previous song. The number of beats used in the spread is a subjective decision based on the general flow of the album. This is simply one method for determining the spread, but the general idea is to use the spread to further amplify the intended feel or experience of the project and can result in varied spaces between different songs.
Spread is also sometimes referred to as the width of a stereo image. The “stereo spread” of a recording refers, in a general way, to how far left and right various sounds are panned. What is usually being described is the subjective assessment of how “wide” the recording is in terms of the perceived soundstage. Some signal processors employ a spread parameter that may use any of a variety of techniques to manipulate a signal so its width or stereo spread can be increased or decreased.