Tempo Mapping In Digital Performer

Create a Grid to Match Recorded Parts
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Above: Detail of Digital Performer's Sequence Window: When Digital Performer’s “Automatically Analyze Beats in This Project” and “Automatically Analyze the Tempo of Audio That Has No Tempo” settings are checked, beat information is displayed in the soundbite.

Create a grid to match recorded parts

EVERY SO often, you need to deviate from the normal recording process. Suppose for example, that a singer/songwriter demos a song with guitar and vocal, and that demo turns out to be a "keeper." Overdubbing a live rhythm section to those parts is not the easiest thing in the world, even for experienced musicians. Having a click track as a reference would make overdubbing easier, but if the original was played without a click, you'll need to create one that follows the audio. This is known as a tempo map and is accomplished in Digital Performer by placing control of the tempo under the Conductor Track. There are many ways to add tempo data to the Conductor Track, such as manually inserting a tempo change, or analyzing an audio file for tempo data and applying it to the conductor track—which is what we're going to learn here. The tempo map will give us a click that respects the artist's original performance while allowing overdubs to be referenced to a grid that matches and moves (or not, if you ultimately quantize) with the original tracks.

Open a new session in Digital Performer and import the reference audio. For the time being, we’ll deal with one audio track, but these concepts can be applied to multiple tracks.

Drag the audio file from the Soundbites window into the Sequence window. Leave a bit of room at the start of the sequence; I like to drag the start of the audio file to the beginning of bar 3. Do not edit the audio file. Under DP’s Take menu in the Sequence window, you can duplicate the track and work on the copy if you prefer.

Two important DP settings are in play here, and they can be found under Preferences>General>Background Processing>Automatic Beat and Tempo Analysis.

Digital Performer will extract and display your tempo data. These settings are Automatically Analyze Beats in This Project, and Automatically Analyze the Tempo of Audio That Has No Tempo. If these are checked, you will see beat information in the soundbite, as seen in the screen shot above. (These are the blue-gray vertical “ghost” lines in the soundbite.) If you do not see beats in the soundbite, command/double-click the soundbite to open the Waveform Editor. Select the entire waveform. Under the Beats menu, choose Find Beats in Selection. DP will go to work, analyzing the file for beats. This may take a moment, depending upon the length and complexity of the file, and CPU speed. Click on the Beats tab and you’ll be able to see the results.

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Return to the Sequence window and select the soundbite. Under the Audio menu, choose Adjust Beat Sensitivity (control-D) and move the slider until you see the strong beats in the audio file. Then click Apply.

Back in the Waveform Editor, click the Tempo tab. Depending upon the Preference settings, DP may or may not have automatically analyzed the file for tempo data. If you don’t see tempo information, select all and under the Tempos menu choose Analyze Soundbite Tempo. DP will extract and display the tempo data.

You now will see a sync point in the soundbite window—a small black triangle pointing downward, probably directly below a transient (also shown in the screen shot). Listen to the file and determine which beat the sync point falls on, musically speaking. For example, if it is on a “1,” drag the soundbite so that the sync point snaps to the “1” of a nearby measure. (Make sure that Snap to Grid is on.) If the sync point is in an odd place, you may need to clear it (select the soundbite and choose Clear Sync Point under the Audio menu). You can then double-click the I-Beam cursor to a new location and choose Set Sync Point under the Audio menu. I find it helpful when the sync point is a strong downbeat near the start of the audio file. Listen to the session with the click on. The click should coincide with the sync point, but probably has little relevance to the rest of the audio file.

In the Sequence window, select the soundbite. Under the Audio menu, choose Adjust Sequence to Soundbite Tempo. If Tempo Control is not set to Conductor, DP will ask you if you wish to switch it. Do it. The sync point should stay where you laid it, and the tempo data will be imported to the Conductor Track. The remainder of the sequence will now conform to the audio.

Listen to the session and you’ll notice that (a) the click follows the audio and (b) tempo is established at the beginning of the soundbite, thus giving you a count in. Depending upon how rhythmic the audio was, and how sharp the transients, click and tempo should now line up with the audio.

If the Conductor Track needs tweaking go to the Project menu, choose Modify Conductor Track>Adjust Beats. Drag Beats in Edit Window should be checked, as should Apply Adjusted Beats Until End of Sequence and Preserve Realtime Performance. For Adjust: you can choose Measures or Beats. At this point, it probably makes sense to Adjust: Beats. Set Snapping to Notes or Audio Beats, which will enable you to snap a bar/beat indicator to line up with a beat in the soundbite. Be aware of the fact that if you close this window, the function is suspended.

When you lay your cursor over the soundbite file, it turns into a double-sided arrow with an anchor at the bottom. This tool will let you snap bar and beat lines in the Conductor Track to the beats in the analyzed audio, thus aligning the click to the performance. I find it helpful when doing this to turn on Auto Rewind, and as I progress through the file move the memory start time forward.

You now have a tempo map and click that other musicians can use for overdubbing purposes. In the future, we’ll look at how to use this to quantize audio to the grid.

Steve La Cerra is an independent audio engineer based in N.Y. In addition to being an Electronic Musician contributor, he mixes front-of-house for Blue Öyster Cult and teaches audio at Mercy College Dobbs Ferry campus.