Using Tempo Mapping to Fix Tempo Drift

What do you do when you want to add ACID loops to a live song? The problem with live music is that is usually not performed to a “click-track” and the tempo drifts so that the ACID Beatmapper cannot be used. The answer is simple. What you need to do is something I call “Tempo Mapping”. Unlike beatmapping which adjusts the tempo of the song to match the project, tempo mapping adjust the tempo of the project to match the changes in the live feel of the song.

To do this:

1. Add the song to your project as a One-Shot (this is important because you don’t want ACID changing the tempo of the song). If the Beatmapper dialog comes up when you add it, just dismiss it.
2. Set the tempo of the song to roughly match the song. This particular song is around 125 BPM
3. Next drop a Tempo Marker (T) at each measure if the song. These temp markers will be used to map each measure to match the live feel of the song (hence the term “tempo mapping”)
4. Play the song and tap the H key on each downbeat (the H key drops a Time Marker) If your timing is a little off, you can go back and adjust them later to be sure they land right on the downbeat. If you do, use the Shift key to avoid snapping as you move.Let’s take a moment to visually see what is happening here. Look at how the distance between the Tempo Markers which are set to the first beat of each measure, and the Time Markers which are the actual downbeats drift further apart over time. You can actually see the tempo drift!

5. Here is where the magic happens. Place your cursor at the Tempo Marker, Right-click the Time Marker and Select “Adjust Tempo to Match Mark to Cursor”. This adjusts the tempo of the previous tempo marker so that the time marker (the downbeat) matches the cursor (which you placed at the start of the measure).Now your downbeat starts at the beginning of the measure. Repeat this for all of the temp markers. Place the cursor on the tempo marker, right-click the time marker, and select “Adjust Tempo to Match Mark to Cursor”.

   Notice that your finished project now has a new tempo for each measure which brings the downbeat at the start of the measure.

The reason this works is because Time Markers mark “wall-clock” time or “absolute” time and Tempo Markers mark “relative” time of the beat. What you are saying is that you want the absolute time of the downbeat to match the relative beginning of the measure. The “Adjust Tempo to Match Mark to Cursor” function in ACID is a powerful and often overlooked feature that can make easy work out of mapping songs with temp drift.

Happy Editing,

Johnny “Roy” Rofrano

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