Apple Logic Pro 9''s nondestructive time-stretching engine, Flex Time, combines elements of beat and transient detection with time-compression and -expansion
algorithms. It is a simple, elegant time-manipulation method that you can apply as easily to a single note as to elaborate multitrack recordings. And like all great DAW functions, you can use it for corrective purposes and abuse it in creative and imaginative ways. In this article, I''ll start with the basics and then take Flex Time editing outside of the box.
Apple has done a great job with the
Flex Time user interface to avoid unnecessary complexity. At the heart of the Flex engine are six separate algorithms designed for either time compression and expansion, manipulating invisibly sliced segments, or speeding up and slowing down audio. These algorithms, called Flex modes, determine how the audio will be altered. They are track-based, and the first time you invoke one, Logic will analyze the track''s audio files for transients and provide a grid of transient markers.
In its simplest incarnation, the transients grid is used invisibly by means of the Flex tool. In other instances, the grid is visible in the Arrange window''s Flex view and is used as the basis for manipulating audio using Flex markers you create. Alternatively, you can edit the transients grid in the Sample Edit window. Transient detection is the fuel that runs the Flex engine.
À LA MODE
The first step in transient detection is choosing one of the Flex modes. They are selected either in the track parameters section of the Inspector, the Flex mode dropdown menu (which is visible in the Arrange window when in Flex view), or the dialog box that comes up the first time a region is clicked with the Flex tool.
FIG. 1: The first time a region is clicked with the Flex tool, you are prompted to select from one of the four basic Flex modes.
When you click on a region for the first time with the Flex tool, you are prompted to choose one of the four main Flex modes. A convenient disclosure triangle reveals a description of how each mode works (see Fig. 1).
Slicing mode delivers on the slicing option that Logic''s Strip Silence has been promising for the past decade or so. It creates invisible slices at the transients and plays each slice at its original speed. Instead of applying time compression or expansion like the other Flex modes, the release phase of each slice is extended (or truncated) to fill to the next slice. This mode is ideal for drums and percussion, and it''s great for quantizing multitracked drums.
Rhythmic mode is best used on simple rhythm-guitar and keyboard parts. Monophonic mode is for single-line pitched material, such as vocals or bass, whereas Polyphonic mode uses phase vocoding and is intended for complex harmonic material. Two other Flex modes, Tempophone and Speed, are available in Flex view or from the track parameters, and they are intended more for sound design than time correction. More on these later.
LEAVE ME OUT
Once a track''s audio files have been analyzed, you''ll see a new Flex checkbox in the Inspector''s region parameters. You use that to deactivate Flex for individual regions, which is great for isolating small sections from Flex processing. For example, you can preserve short drum fills while quantizing the rest of a freely recorded drum track. One caveat: If you change Flex modes after disabling specific regions, they will all be reset with the new mode. So make sure to decide on your algorithm before cutting up and isolating sections of your files.
FIG. 2: The Flex channel parameter is used to set the Flex mode and its related parameters for an entire track. You can disable Flex mode for individual regions in the Region Parameter box above.
The Flex modes are also assignable from the track parameters or from the dropdown menu within Flex view. With grouped tracks, the Flex mode is applied to all tracks in the group. Holding the Shift key down assigns the chosen Flex mode to all tracks in the project, or when working within a folder, to all tracks in that folder. Additional Flex settings are visible in the track parameters, and they update to match the Flex mode being used (see Fig. 2).
Once you''ve chosen a Flex mode and Logic has finished its transient detection, you''re ready to start flexing. You''ll need to choose between the Flex tool and Flex view. The Flex tool forces you to work blind but provides quick access to the main functions while automatically taking care of some important behind the scenes details. That''s adequate for simple edits.
When positioned over the waveform, the Flex tool icon updates visually to indicate transients. That''s extremely helpful for most corrective edits. All you need to do is click and drag directly on the waveform with the Flex tool to stretch or compress the underlying audio.
Although you can''t see it, Logic automatically creates three Flex markers as soon as you drag across the waveform with the Flex tool. One is directly under the original mouse click, whether on a transient or not, and the other two are at the previous and next transients; those act as boundaries to restrict the area being stretched or compressed.
IT'S A SNAP
The position of the Flex tool is tied to the Arrange window''s snap value. That is useful when you want to quickly snap a transient to the grid. And like all dragging in Logic, you can override snapping by holding the Control and Shift keys.
Click at the upper-right region boundary with the Flex tool, and the normal resize tool changes to a special Flex resize tool that allows you to stretch or compress the contents of the entire region. The difference between this and the old method of Option-dragging the right region boundary is that this is nondestructive. Set the Flex mode to Off, and the region snaps back to its original length and duration. A fringe benefit of the Flex engine is that the audio on Flex-enabled tracks follows the project tempo just like an Apple Loop (see Web Clip 1).
FIG. 3: The green and orange shading indicates the degree of time compression and expansion when dragging a Flex marker.
You also use the Flex tool to shift
marquee-selected sections of a waveform horizontally in time. When dragging a
marquee-selected area with the Flex tool, Logic creates four Flex markers (which you can see in Flex view). They are at each of the selection boundaries, as well as at the previous and next transients. In theory, this should always let you move the selected area in time. In practice, it works best if there is a clean break from the audio immediately adjacent to the selected area.
Logic processes the audio either between the first and second Flex marker or between the third and fourth. The portion between the second and third Flex marker is left unaltered. For single bass notes, clean rhythmic chords, vocal phrases, and isolated drum hits, this works great. But if there is any audio in the waveform at the selection boundaries, flexing it will produce noticeable artifacts.
A BETTER VIEW
As efficient as the Flex tool is, Flex view gives you finer control over the creation and editing of Flex markers, and that lets you manually alter the timing of audio material. You enable Flex view from the shortcut menu at the top of the Arrange window, from the View menu, or by key command (Command + F).
In addition to displaying the Flex mode dropdown menu and Flex markers, Flex view displays the transient grid as thin gray lines. A high zoom level gives you finer precision with your mouse. The pointer and marquee are both useful for creating and manipulating Flex markers, so it is a good idea to have the marquee assigned as your alternative tool.
You create Flex markers—either between or directly on top of existing transient markers—by clicking in the upper half of the waveform with the pointer. The tool icon visually updates when positioned directly over a transient.
COLOR MY WORLD
Dragging a Flex marker to the left compresses the audio between the marker and the beginning of the region as it expands the audio after the marker until the end of the region; dragging right does the opposite. Time compression is displayed in increasing shades of green, whereas expansion is displayed with increasing shades of orange (see Fig. 3). When extreme compression is applied, the green turns to red and a warning message appears.
FIG. 4: A yellow guideline helps you snap Flex markers to transients on vertically adjacent audio or MIDI regions.
If you want to alter only a portion of a region, use additional Flex markers to restrict the area being compressed or expanded. Click in the lower half of the waveform, and the pointer sprouts three prongs to indicate that three Flex markers will be created: one where you click and one each at the previous and next transients. Just like with the Flex tool, the outer markers act as boundaries when dragging the center marker. Drag past the left or right marker, and it will jump to the next available transient, increasing the area being flexed on the fly.
You work with marquee selections in Flex view the same way you do with the Flex tool. Create a marquee selection and click in the upper half of the waveform. Four Flex markers are created: two at the selection borders and two at the adjacent transients. When moving the selection, only the audio outside the selected area will be altered. Alternatively, click in the lower half of the waveform to create three Flex markers: one at the location of the click, whether on a transient or not, and one at each border of the selection.
If you aren''t happy with the results of your Flexing, control-click on the Flex markers to bring up a contextual menu where you can choose to either reset them to their neutral positions or delete them. Double-clicking the Flex markers or clicking on them with the eraser tool will also delete them. Control-click in the region background to delete all Flex markers at once or to slice the file up based on the transients.
Hold down the Option key while dragging a Flex marker to reposition it without time stretching the underlying audio. Option-dragging the right region boundary while in Flex view enables the Flex tool resize function, which lets you compress and expand the whole region nondestructively.
Like the Flex tool, Flex markers are tied to the snap grid, but you can easily align them with transients in vertically adjacent audio or MIDI regions. Click-hold a Flex marker and drag the mouse upward or downward over an adjacent track. A yellow guideline appears, allowing you to snap the marker to the other region''s transients or, in the case of MIDI regions, to its notes (see Fig. 4).
SLICE OF LIFE
To quantize multitracked drums, ensure that all their start and end positions are the same and then assign them to a group and enable Editing and Phase-Locked Audio group settings. A new Q Reference button will appear in the track header of each grouped track. Disable these buttons from either the track header or the track parameters on all but those tracks whose transients you want used as the basis for quantizing the group. In practice, kick and snare drum tracks work well for this because they tend to have the strongest most regular transients.
Open each of the Q Reference tracks in the Sample Edit window and enable Transient Editing mode either from the local View menu or from the shortcut button. After an initial transient-detection analysis, markers will be placed at all the transients and the grid will be visible and editable.
FIG. 5: You can create and edit transient markers in the Sample Edit window when Transient Editing mode is enabled.
Make sure the transients are situated correctly in the waveform. Logic does a good job of analyzing the audio, but you can adjust the transient sensitivity threshold by clicking the “+” and “-” buttons. You can create transient markers manually with the pencil, move them with the pencil or pointer, and delete them with the eraser or by double-clicking on them (see Fig. 5).
Once the transients are correct, enable Slicing mode in the Arrange window. Quantize markers become visible and are displayed as a solid white line. With all the tracks in the group selected, choose a quantize value from the Region Parameter box, and the quantize markers will snap into position. Lower quantize values with positive Q-Range values generally work best. That allows notes farther from the grid, such as rolls, to be preserved (see Web Clip 2).
The slice-length parameter, available in Slicing mode, is used to shorten each slice by a percentage. You can use this creatively with Logic''s new speed fades—a nice fringe benefit of the Flex speed algorithm—to add some spice to flat-sounding loops.
Copy a loop onto an adjacent track, set it to Slicing mode, and set the channel parameters'' slice length to taste. Control-click on the region and choose Slice At Transient Markers. (It would be a nice addition if the newly created slices reflected the shortened slice length.) With all of the newly created slices selected, add some speed fades from the Region Parameter box, delete some of the slices to create some space, and mix it all in with your original.
Stretching the copied loop on a track with Flex set to Speed mode creates another nice pitch-style effect. After stretching or shortening (lowering or raising the pitch), slice at transients, delete some slices, and mix the rest in with the original (see Web Clip 3)
For granular synthesis-style sound design, use Tempophone mode. Tweaking the grain size parameter works nicely for creating artifacts with a ring modulation type of effect. Lower crossfade parameter values create hard artifacts, which generate interesting delay-type effects. Higher values are smoother sounding. You''ll need to restart playback after you''ve tweaked the crossfade parameter.
Tempophone mode yields the most interesting results when extreme stretching is applied (see Web Clip 4). You''ll find some unusual ways of mangling and abusing the various Flex modes in my video tutorials, available in the Videos > Tutorials section online.
Beyond correcting and mangling audio timing, you''ll find many new Flex Time-related features. Varispeed lets you alter a project''s global tempo. Selective Track Import makes imported tracks conform to the project tempo. Tempo and transient information is automatically stored within audio files recorded in Logic. Convert To New Sampler Track is a wonderful bonus of transient detection. And these are just a few of Flex''s hidden treasures.
Eli Krantzberg is a drummer who swears he never Flex-edits his own drumming. He is also a bandleader, musician, and sound engineer. His video tutorial series,
Flex Time Explained, is available at groove3.com.