Train REX

Using REX files is a great way to add prerecorded beats to almost any project. One advantage of REX files, which are available from many sound developers,
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Using REX files is a great way to add prerecorded beats to almost any project. One advantage of REX files, which are available from many sound developers, is that you can change tempos without compromising audio quality.

To play a REX file with a compatible plug-in, load the file into the plug-in, and then extract the file's MIDI data to a MIDI track in your sequencer using a utility command in the plug-in. (Check the plug-in manual for specifics.)

This data extraction adds two important capabilities to REX-file playback. First, you can reshuffle the individual hits in the REX file or change the feel of the beat by editing the MIDI data. Second, using your sequencer's groove template features, you can turn the MIDI data into a groove template to which you can quantize other MIDI tracks. That is especially useful when you quantize a bass synth to a beat; the rhythm will sound tighter if the bass locks to the drums (see Web Clip 1). Quantizing the bass to regular 16th notes might not do the trick, because the REX-file beat might have a more flexible feel.


But what if you don't have a REX-file player? Like some other sequencers, Steinberg Cubase will import REX files directly into audio tracks. The timing of the original file is preserved, and you can change the tempo. You can easily drag individual hits within the REX file forward and backward in time or to other tracks for separate effects processing.

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FIG. 1: REX files contain some extra audio at the end of each slice so that there won''t be gaps when the tempo is slowed down. When a file is displayed in Cubase at its original tempo, the gray areas indicate overlaps between one slice and the next.

You can't, however, extract the timing information from the REX file so as to quantize MIDI tracks to it. Cubase will create groove templates from audio beats that have been sliced apart using the program's own Hitpoints feature. (For most purposes, using this feature is as good as using REX files, though Cubase's slices lack the overlapping tails found in many REX files, as seen in Fig. 1.) But Cubase can't create a new quantization template from an imported REX file.

If you have Propellerhead ReCycle, you can use it to extract a REX file's associated MIDI file, and then use that as a groove template in Cubase 4. Fortunately, there's an easy work-around for those who don't have ReCycle (see “Step-by-Step Instructions” on p. 68).


First, choose Audio File as the file type to import using the Import submenu of the File menu. In the dialog box, select the REX file you want to use.

Set the left and right locators in the transport to the start and end of your imported REX file. If your project already has some tracks recorded, mute all of the tracks except the one with the REX file, and then choose Audio Mixdown from the File menu's Export submenu. In the Export Audio Mixdown dialog box, make sure that you've checked both of the boxes in the Import Into Project area at the bottom. This will produce a “vanilla” audio track that should sound exactly the same as the REX file.

Double-click on the part containing the new audio to open the Sample Editor, click on the Hitpoint Edit button, and adjust the Hitpoint Sensitivity slider so that Hitpoints show up on all of the attack transients. Then go to the Hitpoints submenu of the Audio menu and select Create Groove Quantize From Hitpoints.

Try Before Buying

Before discarding the new audio part, try out your new groove template to make sure that the quantize template has enough points but not too many. Open up a Key Editor window for a MIDI part that you want to quantize, select the template in the Quantize menu if necessary, and look at how the notes relate to the light gray grid.

If there are notes that fall midway between the grid lines, don't quantize them to the grid. Instead, drag-select a few bars of notes, shift-click on all of the notes you don't want to quantize, and then press the Q key to quantize those that are still selected. Presto — you've just quantized a Cubase 4 MIDI track to a REX file.

You can quantize start times of the slices in a REX file in the Audio Part Editor, as if they were MIDI events. You can easily add swing to a straight-time beat (or vice versa). Or you can import several REX files and extract groove templates from them, and then quantize one file to the groove of another. Using a Latin groove as the source for the template and applying it to a trap-set beat can yield an evocative feel.


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Find a REX file that you like, select an audio track, and use the Import submenu of the File menu to insert it into the track.

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After soloing the track and placing the locators, use Audio Mixdown to bounce the beat.

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Now you have two versions of the same beat, one REX and one plain audio. Here, I''ve dragged the new audio track up so that it''s directly beneath the REX track.

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Open the audio part and create Hitpoints using the Sample Editor.

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While still in the Sample Editor, select Create Groove Quantize From Hitpoints from the Hitpoints submenu of the Audio menu.

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Check out your new groove by quantizing a MIDI part to it.

Jim Aikin writes, teaches, and plays music in Northern California. You can visit him online