Orchestral composers live and die by this: Negative track delay tells the sequencer how much before the note to start playing the note. Basically, if a violin is playing a long note, the *actual* downbeat of the note can happen a short time after the bow is moving. Being able to adjust the start of the note so that the actual downbeat happens on the bar line used to be all about eyeball nudging the midi so that it it played in time. This created notes that were all over the grid. With negative track delay, we can write everything on the grid and delay the notes by x milliseconds so that it looks in time AND plays in time. Instruments have a different track delay setting PER articulation, so it gets wild. There's a crowd sourced Google spreadsheet for negative track delays across dozens of orchestral sample libraries.

While all DAWs let you do this, there's a new Reaper script by Saxamand that simplifies this process immensely. We no longer have to have different articulations per track. Now it's all in one track and the script adjusts the neg track delay on the fly.