A composite variable duration soundtrack for a user to play while reading a text source, the soundtrack duration being defined by a soundtrack timeline. The soundtrack comprises multiple sound layers configured to play concurrently through the soundtrack timeline, each sound layer having an arrangement of one or more audio features that are configured to play at preset start times in the soundtrack timeline. At least one sound layer is adapted for modifying the preset start and stop times of its audio features to match the reading speed of a user based on a reading speed input.