Velocity Compression is used in MIDI sequencing software to emulate the effect of audio compression; that is, to smooth out the transients in a performance without changing the musical dynamics of the piece. Here’s how it works, Each MIDI Note-on message has a velocity value of 1-127. In Velocity Offset, the velocity of a selected group of notes is either boosted or cut in a linear fashion. E.g., with an offset value of +25, three notes originally played at velocities of 78, 111, and 43 would play back at velocities of 53, 86, and 18. With velocity compression, the velocities are multiplied or divided by some number so that the differences between them get larger or smaller. For example, at a compression value 75%, the same three notes would play back with velocities of 59, 83, and 32. What occurs is that the velocity of the loudest note is reduced the most, while softer notes play back closer to their original velocity, helping to keep them audible.