Music production software has a strong tradition of two-dimensional graphical user interface (GUI), in which the time line is represented as a flat composition either horizontally (from left to right) or vertically (from top to bottom). In my degree work titled Sequi, I approach music composition from a different angle. Instead of a two-dimensional time line with only two possibly ways of progression (forward or backward) I constructed a three-dimensional GUI with the maximum of four different ways of progression from any given point in a composition. The height axis is used to describe time-intervals (the time between downbeats) and the wide and depth axes are used to describe progression from one sound to another.