Slice, Move, and Glue

The advent of digital audio sequencers has made quantized drums a fact of life. Here''s how to chop up multitrack audio drum parts and quantize them perfectly in Apple Logic Pro.
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The advent of digital audio sequencers has made quantized drums a fact of life. Here''s how to chop up multitrack audio drum parts and quantize them perfectly in Apple Logic Pro.
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The advent of digital audio sequencers has made quantized drums a fact of life. For a recent electronic project of mine, live drums were overdubbed onto quantized synth tracks, making quantized drums a necessity (see Fig. 1). Here's how to chop up multitrack audio drum parts and quantize them perfectly in Apple Logic Pro.

For this example I used kick, snare, hats, and stereo overhead tracks, but the technique will work with any number of tracks (see “Step-by-Step Instructions” on p. 64). Look closely at step 1, and you'll see that the kick and snare waveforms don't align exactly with the grid lines (see also Web Clip 1).

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FIG. 1: The five drum tracks at the top need to be aligned to the MIDI bass tracks below.

Group Therapy

Cuts and moves must be exactly the same for all tracks; otherwise, nasty phasing artifacts will result. You can use Logic's Group function to ensure that all edits happen simultaneously. Enable grouping by selecting the same group number for each drum audio channel using the drop-down menu directly beneath the channel's track number in the channel strip. Make sure to check the Arrange Select (Edit) box in the Group Settings dialog box. Grouping greatly reduces the number of edits you'll need to make.

It is best to work with one or two bars at a time and to start with eighth-note slices. Select the Scissors tool and cut the kick track at the 2-bar mark. Ensure that Snap is set to Ticks in the upper-right corner of the Arrange window, and then hold the Option key and cut at the first eighth-note grid line. (The Option key activates Logic's Divide Multiple command, automatically making cuts at every eighth note.)

Line 'Em Up

If you zoom in, you'll see that the regions are in perfect alignment with the grid but the audio hasn't been moved; everything will sound the same. Next, move the start time of the audio regions as necessary to have the transients of the waveform line up correctly. Do this from the Arrange window — don't double-click on the waveform.

Zoom in on the region containing the first kick hit and select it. (You can temporarily select the Zoom tool by holding the Control and Option keys.) Choose the Arrow tool, click near the left edge of the region, and move its start point to the beginning of the waveform. Note that because the tracks are grouped, the regions that are vertically aligned with the edited one will have their start points adjusted simultaneously. Repeat this process for every kick and snare hit (or hi-hat hit if there isn't a kick or snare on the beat) that is not already aligned. You may have to move the region start to the left or right depending on whether the drummer was rushing or dragging.

Once all the region starts are correct, you need to move all the regions back to the grid. You can move them one by one, but here's a shortcut. Highlight all of the regions of the section you've been working with. In the Windows pull-down menu, select Event List. In the Event List, click on the Q button and select “⅛-note.” Now all the beats will be quantized (see Web Clip 2). You might also want to do some 16th-note cutting and aligning if the pattern calls for that.

Timely Alterations

The beats are now in perfect time, but there may be gaps between some of them. Here's how you can use Logic's Time Machine to time-stretch those regions and eliminate audio gaps.

At the top of the Arrange window, draw a cycle loop a few ticks longer than an eighth note. Select all the regions within the 2-bar range in which you've been working. In the Arrange window's Audio pull-down menu, select Adjust Region Length To Locators to time-stretch them. Now all the regions will be stretched to at least an eighth note in length. (I recommend making the cycle length a little long because sometimes Logic's time-stretch algorithm calculates on the short side, and it won't hurt if a region is a bit long.)

The beat should sound perfect now (see Web Clip 3). But Logic works harder to play many little chunks, so I glue each track into a contiguous region with the Glue tool. Alternatively, you can select all the regions on a single track and select Merge Regions Per Tracks from the Arrange window's Region pull-down menu. With either method, you need to disable the Group function; otherwise, Logic will mix the grouped tracks down to a single audio file.



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Notice how the kick and snare drum waveforms are shifted a little to the right of the eighth-note grid lines.


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Assign each of the drum tracks to the same group using the channel strip drop-down menu under the track numbers.


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With the Scissors tool selected, hold the Option key and click at the first eighth-note grid line.


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Align the region starts to the beginnings of the kick or snare waveforms. Then quantize the regions to eighth notes in the Event List.


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Use Logic''s Time Machine to time-stretch each region to an eighth note in length.


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Use the Glue tool to merge the regions on each track back into one 2-bar region.

Mitchell Sigman is a Los Angeles-based musician. He plays keyboards in the classic '80s synth-pop band Berlin as well as fronting his own project, Celebutante.