Computer Recording — Pro Tools Beat Detective
Keyboard Magazine
January 2002
By Jim Batcho
One of the most common and time-consuming aspects of modern music production is editing drums. Beat Detective for Pro Tools 5.1 TDM systems aims to make the process considerably simpler, more automated, and more successful. In basic terms, Beat Detective is a multitrack rhythm analysis and conforming utility designed to tighten recorded material that has well-defined peak transients. On the simplest level, Beat Detective can slice drum tracks into individual audio events similar to how ReCycle works. However, Beat Detective also offers groove extraction, automatic tempo map creation, and region conforming (quantizing) to a groove or grid. It can automatically trim or time-stretch and crossfade individual slices, resulting a more natural-sounding track than you'd get from simply slicing and moving individual audio regions.
A broad tutorial on this deep software is beyond the scope of what we have space for here. Instead, I'll take you through the most typical use of Beat Detective — tightening a multitrack drum performance. If you're not already familiar with the controls and terminology of Pro Tools and Beat Detective, the user manual will come in handy as we go. I'll assume you're familiar with typical Pro Tools terms — "regions," "groups," "memory locations," and the like.
Before we get started, a disclaimer: Although Beat Detective makes editing multitrack drum performances quicker and can yield far better results than manual editing, using it is rarely completely automatic. Beat Detective requires a bit of trial and error. If you're using the Edit Smoothing feature (which automatically creates crossfades at edit points), Beat Detective also requires plenty of RAM devoted to Pro Tools — at least 100MB. Additionally, you should have sufficient hard drive space to handle all the regions created.
Getting Started
Beat Detective is divided into four main operations: Bar|Beat Marker Generation, Region Separation, Region Conform, and Edit Smoothing (see Figure 1). All four have various sub-operations, but we'll expand only on certain aspects here with the aim of giving you some time-savers and methods for improving success.
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Once you have your drum performance tracked and comped, and the arrangement is to your liking, open the Beat Detective window and enter the time signature of the song. Take all the disparate drum tracks (kick, snare, hat, toms, overheads, etc.) and create a "Drums" Edit Group for them. Once the group is established, disable all Edit Groups (Command-Shift-G); you'll re-select (enable) the drums group again later.
The next step is to define the selection or section you wish to edit. It's best to select smaller sections of material (say, 16 or 32 bars) and conform them one by one. The smaller the selection is, the better chance Beat Detective has at locating and defining bar and beat markers correctly. If you're working with an average-length pop song, you can try tackling the song in sections, such as Intro/Verse 1, Chorus 1, Verse 2, Chorus 2, Bridge, Solo, Chorus 3/Outro.
With Beat Detective it's important that you properly define the selection. The beginning and end points of the selection must fall squarely on the beat. An excellent way to define a selection is with the Tab to Transient option in Pro Tools. Make sure the Tab to Transient icon is selected in the Edit window (see Figure 2 on page 68), then zoom far enough out to see the entire area you intend to select. Go to the first track in the drum performance and click in the area just before the transient peak that you want defined as the beginning of your selection. Press the Tab key. Beat Detective will automatically move the selection start point to the transient peak. With the Shift key held down, click just before the next transient peak and press Tab again. The selected region of audio starts precisely at a transient and ends just before the next transient.
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Another time-saver is to enable the single-stroke command key focus in Pro Tools. This way you can use the P and semicolon keys to move the selected area up and down. For example, say the best-defined transient point in the entire drum performance is the snare drum (track 2), but you'd rather start with the kick (track 1). With the command key focus icon enabled, you can use the snare to define the selection, then hit the P key to move that selection up toward the kick drum track and begin the Beat Detective process from there. The P and semicolon keys will also come in handy when using Collection Mode, discussed later.
With Link Edit and Timeline Selection and Loop Playback checked in the Operations menu, play the selected loop until it wraps back around to the beginning to audition your selection. Once you're satisfied with your loop, create a memory location out of it (creating a Selection instead of a Marker). Before moving on, unlink the edit and timeline selection so you can click outside the selection without de-selecting it.
Analyzing Tracks
Re-enable the drum edit group, and click on the memory location. Open the Beat Detective window and set your selection parameters and time signature. Click the Analyze button and move the sensitivity slider until the proper trigger beat points are identified. If the performance is based more on straight quarter-notes, click the "Beats" option. Switch to "Sub-beats" if the drummer's performance is more intricate. Listen back to the performance as you analyze, and follow where the hits are playing and whether the trigger points are landing on the correct locations. Pay close attention to where the trigger points are landing, because this will determine how successful your automated edits are.
With the Show Trigger Time selected, Beat Detective will display the specific subdivision location that Beat Detective interprets as the correct hits. With most pop drums, false trigger points shouldn't be a problem. If false trigger points are created, though, you have several options. You could go through the entire selection and manually insert, delete, move, and promote trigger points using the Grabber tool. But this can become time-consuming work if there are many false triggers over a large multitrack selection. If you find you're running into trouble, you can try enabling Trigger Padding and, if necessary, use Collection Mode.
Trigger Padding can be used in conjunction with Collection Mode or by itself. Essentially, with Trigger Padding the trigger point times are offset (padded) to account for the slight delay that occurs between close-miked individual drums and more distant overhead mics, or when crossover bleed occurs between two close-miked instruments.
To use Trigger Padding, simply enable the drum group, set the trigger pad value, and separate the regions. If necessary, go back and re-adjust the pad value as needed. Experiment with the number of milliseconds you need to push the trigger point back earlier in the tempo map. You can enter values up to 50ms, but a setting of 10ms is a good place to start. If Trigger Padding is successful, generate the markers.
If Trigger Padding isn't giving you the results you want, the next option is to use Collection Mode. This allows you to go through the multitrack drum group track by track and create a "collection" of trigger points. Collection Mode should only be used with close-miked material (kick, snare, toms). Using this mode with overheads and other, more distant-miked material will create unsuccessful edits once you conform the regions. You can imagine how Trigger Padding can be used in tandem with Collection Mode — the former for distant-miked instruments and the latter with close-miked instruments. Normally, however, you should try getting good results with Trigger Padding first, then use Collection Mode if needed, and use both as a last resort. One of the great benefits of Collection Mode is that it allows you to define the transient analysis algorithm used on a track-by-track basis. For example, since the kick drum generally resides in the lower end of the frequency spectrum, you can select "Low Emphasis" and Beat Detective will extrapolate transient points with an emphasis on the lower frequency range.
To begin collecting information from disparate tracks, disable your drum edit group again and click on your memory location. In this case, with the group off, it should highlight just the previously selected area of the first track in the performance (i.e., the kick track). Select "Low Emphasis" for the kick, and go through the normal analysis operations covered previously to create trigger points. Click the Generate button and then click the Collection Mode button. In the dialog box that appears, click Add to add the kick track to the collection. With Key Commands Focus enabled, press the semicolon to move down to the next close-miked track (remember to skip all distant-miked material). When the selection moves down, it will display the transients of the previous track, so you need to re-analyze and regenerate the second track. If the next track is snare, select High Emphasis and repeat the analysis, generation, and collection process. Continue until you have all the triggers for the disparate tracks that you need to collect. Once you've collected together the necessary transient points across all chosen tracks in the performance, re-enable your drum edit group and shift-click another non-selected track in the group to select everything you want to conform.
Conforming
You're finally ready to separate the regions and conform the drum performance to Pro Tools' grid/tempo map. Separating regions is a fairly straightforward process if you've successfully defined the trigger points. If there are 64th-notes or triplets, indicate so in Beat Detective's check boxes. Click the Separation button to separate the regions.
Next, conform the regions to the established tempo map. It's tempting to play with the Strength, Exclude Within, and Swing quantize features when conforming a performance. Before doing this, try leaving Strength and Exclude Within unchecked and instead concentrate on the Swing value if the performance already has some swing to it. If there is no swing at all, start out by leaving all boxes in this area unchecked. You can always undo, go back, re-check items, and move their sliders if needed.
If the performance has any degree of swing to it, the Swing slider in the Region Conform section is crucial. In most cases, the swing value should be sixteenth-note swing. Experiment with Swing and conform, undo, and re-conform as necessary.
The final step with Beat Detective is Edit Smoothing. This is where the real magic of the application comes through. The Edit Smoothing process automates what would otherwise take hours of work by filling and crossfading the transitions between regions. Once you've completed the smoothing process and the results are to your satisfaction, move on to the other sections of the song and beat-detect them section by section in the same way we've described.
After you've conformed the entire drum performance, it's a good idea to consolidate all the regions of audio using the Edit > Consolidate Selection command. This command joins the files represented by your selection into a single, new audio file — one for each track. Since literally hundreds of regions with crossfades can be automatically created using Beat Detective, consolidating them minimizes any potential hard disk seek problems you could get because the disk may be too slow or fragmented to keep up. Note that any muted sections will become silenced with the Consolidate Regions command.
Feel free to go back and undo any of your operations to try different parameters. Once you're comfortable with the application, you'll find many uses beyond just tightening multitrack drums. There are some excellent creative options. One possibility is to take a drum machine loop, have a live drummer play to the loop, then conform the loop to the drummer's feel. Then you can delete the drummer's performance and have a mechanized sound while retaining the feel of the live drummer. Experiment.
Biography
Jim Batcho (jimmythejim@yahoo.com) is a freelance drummer and writer living in San Francisco. Special thanks to Dave Lebolt of Digidesign for his help with this article.
Article courtesy of Keyboard
