We show you how to make a tempo map with Beat Detective.
Beat Detective is normally used for one of two things. The first is to make recorded drums lock in with loops, MIDI or a click track; the second is to leave the timing of a drum recording unchanged, but to use that timing information to create a tempo map so that you can pull other material in and have it locked in time with the drums.
I’ve always preferred the latter approach where possible, but that assumes that the drummer was playing well and holding the band together like a good drummer should, and also that the recording was a traditional band recording capturing a group of players in the room at the same time playing together. Being able to build an accurate tempo map around that recorded performance will let you bring in loops, sequences and other forms of ear candy that can really elevate a track, and while recording to a click can achieve much the same, it’s often very unpopular with bands who are used to playing live. This is where Beat Detective can really help.
In SOS October 2020’s Pro Tools column I covered the biggest obstacle to using Beat Detective on a track which wasn’t recorded to a click: the fact that the session’s grid is unrelated to the audio recorded. There is a feature in Beat Detective which can help with this but I’ve always found it more straightforward to do the first steps manually. Many of the features of Beat Detective are available as manual operations elsewhere in Pro Tools, but as we’ll see the Beat Detective interface is essentially a big macro of these functions, and it can perform many of the tasks semi‑automatically.
The example of this semi‑automation I’m going to concentrate on here is the generation of bar and beat markers. There isn’t any practical difference between using the Identify Beat command, as used in last month’s column, and using Beat Detective to create bar and beat markers. The only difference is that Beat Detective creates them automatically.
This is where the biggest caveat to using Beat Detective comes in. It’s really important to check everything Beat Detective does because while it’s fairly good, it often gets things wrong. If it was your assistant you’d tell it to slow down and pay more attention!
Creating a tempo map is straightforward as long as you check your work, and work through the song one short section at a time. The temptation is to make a big 80‑bar selection and hit Generate, but while this might work on very straightforward material, once you have had a problem with Beat Detective misinterpreting the audio you’ll end up spending longer figuring out what went wrong than it would have taken to work in smaller selections. Trying to rush is a false economy. It only takes a single bar of 2/4 you hadn’t noticed to throw everything out!
The most important thing is to check your selections. Use Tab to Transients to Tab up to the downbeat of the first bar of your selection, and if you can visually identify the corresponding downbeat four or eight bars later then Shift‑click just before it to extend your selection to that point and, while still holding Shift, hit Tab to move the selection up to the downbeat. If you’re finding it difficult to visually identify the correct beat to start or end your selection on, you can hit the down arrow during playback to set the ‘in’ point of your selection and hit the up arrow to set the ‘out’ point. These will probably be a little off, but holding Shift while dragging or using Tab to Transients will get things lined up neatly.
While most of the time it’s pretty clear where the current start and end points are for your selections, the best way is of course to listen. Hitting Command+Shift+L to loop playback and make sure that your selection is correct is fine for short selections, but waiting for eight bars just to check the loop point is a huge waste of time. A far quicker way is to go into the often forgotten Dynamic Transport Mode, introduced way back in Pro Tools 8. Hit Command+Control+P to switch to Dynamic Transport (Screen 1, above), and move the blue Play Start triangle to just before the loop point to audition the loop without wasting any time!
If it feels like I’m labouring the point about being careful with your selections that’s because I am. After all, garbage in equals garbage out, and most of the problems I’ve experienced using Beat Detective stem from incorrectly defined selections.
Most of the problems I’ve experienced using Beat Detective stem from incorrectly defined selections.
Once you have a correct selection in the Beat Detective window (hit Command+Num8 on a Mac or Control+Num8 on a PC if you don’t already have it open), and if you have followed the steps to set a starting tempo using the Identify Beat command as outlined in last month’s column, then the selection made on the timeline should correspond with the displayed start and end selection values in the Beat Detective window. If there is a discrepancy then it is important to correct it at this stage. Always check that the number in the selection field matches your expectation. In most cases just hitting Capture Selection will transfer the currently defined start and end points of the current edit selection into the Beat Detective window.
If the selection isn’t what you’d expect there are two possible reasons. Either you have defined your selection incorrectly, or the tempo of the audio differs from the session tempo (ie. the audio slows down or speeds up compared to the current session tempo). If this is the case you need to check which it is by playing the audio. You can audition against the click, but this can be pretty cacophonous so my preference is to audition the audio against the bars and beats counter. Use the Big Counter if you like (Command+Num3 on a Mac, Control+Num3 on a PC).
If you have established that the selection is correct but the tempo differs significantly from your session tempo it is possible to use the much misunderstood/ignored Tap B|B button to help Beat Detective understand the tempo of the material semi‑automatically (Screen 2). Lots of people seem to give up on the Tap B|B button when they tap it and nothing seems to happen. In last month’s column I explained that Tap Tempo isn’t accurate enough for tempo mapping, and while that’s true, if you define an accurate edit selection, preferably starting on beat 1 of a bar and ending on beat 1 of a bar a known number of bars later, you can tap along in time with the audio and Beat Detective will calculate the correct end time. You have to enter the correct start time and meter, and then just hit play and start tapping. It’s tempting to try this with very long selections but I’ve found this to be a false economy in the past.
Once you have your selections properly defined, generating bar/beat markers is as simple as choosing the bar/beat marker generation button in the left of the Beat Detective window, selecting your chosen Analysis mode (I rarely find I need to use anything other than Enhanced), and pulling up the sensitivity slider until all the beats are detected. If you are generating Bar markers then that is all there is to it. If you are generating sub‑beat markers, which for the purposes of tempo map creation will mean that the tempo map, and anything quantised to it, will follow the timing variations within the bar more closely, you will need to correctly identify the smallest subdivision contained in the audio. It might be tempting to leave it at 16th notes, but if there is no subdivision smaller than an eighth note in the recording then you run the risk of an early or late note being pulled onto the wrong subdivision, so make sure this setting is set as coarse as possible. The same is true when setting grid settings for quantising.
When creating bar and beat markers you might find that you have a reluctant beat which needs the sensitivity slider pushing way higher than is necessary for the rest, or that doesn’t even get detected with the slider all the way up. If this happens, push the sensitivity just as far as is necessary to detect the rest of the beats, and then manually delete, create or move markers using the Grab or Smart Tool. Click‑drag a marker to move it; Alt‑click to delete it; or simply click to create a new one. Click on the bar, beat and sub‑beat radio buttons to see what the different thicknesses of purple markers mean. Logically enough the thickest lines are bars and the finest are sub‑beats.
When you’ve detected all the beats you intended to and checked they are accurately placed, hit Generate. You’ll get a warning asking what you want to do about tick‑based tracks. Audio tracks recorded at the same time as the drums are likely to be sample‑based, but as MIDI and instrument tracks usually default to being tick‑based you might need to take care here, as their tick position won’t be meaningful and you would want to preserve their sample position.
At this stage you should have a detailed tempo map, as in Screen 3. If it was generated using Bar as the resolution the tempo should be consistent, and if it isn’t you can use it as hard data to shame the drummer (but don’t do that, it’s mean). If you are seeing consistent variation between beats then that is groove and it is a good thing, but if you’re seeing rogue variations it is worth investigating more closely. It might be because of misplaced markers.
The easiest way to spot misplaced markers is to look for suspicious variations in tempo. While they might be right, if they are inexplicably off, particularly if a neighbouring tempo is off in the other direction, that suggests something is wrong. These are much easier to spot if you expand the tempo ruler to show the tempo graph rather than just the markers.
There is a lot to say about Beat Detective but if you want to use it to support a good drummer rather than fix a bad one, then tempo mapping is the feature you should check out.