Using Logic's Time & Pitch Machine

Logic's Time and Pitch Machine offers a number of different time-stretching algorithms to suit different types of material.

Here's how to manipulate pitch and time in Logic Pro X.

While programs such as Ableton Live are well suited to those who work almost exclusively with loops, Logic Pro X is quite adept at 'making things fit' when necessary. This month's Logic column is mainly about fitting things in the time domain, but I'll include some of the related pitch features as I go along. I don't claim this to be an exhaustive examination of the subject, but rather to shine a light on the features that I use on a regular basis and to point out some of the pitfalls.

Both time and pitch can be manipulated in a number of different ways in Logic Pro X, primarily via either the Time and Pitch Machine or via Flex Time/Flex Pitch. However, before you can use these you'll need to make sure Logic's Advanced Tools are turned on in Logic's Preferences, as when you first install Logic Pro X, they are turned off to ease the learning curve. There's also a basic Pitch Shifter plug-in as well as a Pitch Correction plug-in, plus the ability to stretch individual audio and MIDI Regions without having to invoke any special features if you don't need anything too complicated.

Machine Learning

The Time and Pitch Machine is located under the Functions menu of the Audio File view (Command+6). When you open it, you'll see at the top of the window that you can use either Free or Classic modes. There's also a choice of algorithms to best suit the type of material being treated, the default being Universal. For drums or percussion the Beats and Percussion options preserve timing best, while the Pads and Complex settings prioritise smoothness of pitch-shifting. Free mode, which is the default, allows pitch and tempo to be changed independently of each other, while Classic mode works like old-school tape varispeed, increasing the pitch as you increase the tempo. As a rule you'll want Free mode, where you simply enter a destination bpm and the audio in the selected Region will be converted to fit without changing pitch once you hit Process and Paste. If you do need to change pitch, there's a Transposition box in the lower-right corner, and a Preview button lets you hear the result before you commit. Time and Pitch Machine has been in Logic for a long time, but for some jobs it still produces more consistent results than Flex Time.

Flexible Working

Flex Time is useful if you have a project that needs to be changed in tempo, or if you have parts of the wrong tempo that need to be imported. Let's say you have a project at 80 bpm but the drum loop you want to import is only 57 bpm. One easy option is to temporarily change the project tempo to 57 bpm, import your drum loop by dragging onto a new audio track, switch on Flex time for your new track (the symbol between the Automation and Catch buttons, to the right of the Main page view button), and then enable Flex Time by clicking on the butterfly-shaped Flex symbol in the track header of your imported drum track. In the menu bar directly below, select Rhythmic or Slicing (the most appropriate Flex processes for drums). Don't turn on Flex for any other tracks. Now change the tempo back to 110 bpm, and your drum part will adapt automatically. To make the change permanent, bounce the Flexed drum part to a new track using the 'Bounce Region in Place' or 'Bounce Track in Place' command from the main File menu. I usually select the option of bouncing to a new track without effects so that I can check the results before deleting the original.

Flex Time is potentially very powerful and allows us to correct small timing errors or to nudge backing vocals into line with a lead vocal very easily.

Should you want to change the tempo of an entire song/project, the MIDI and drummer parts will automatically conform to the new tempo, but to get the audio tracks to move with them, you need to select Flex for all of the audio tracks, then select the appropriate Flex algorithm for each track according to the type of audio you are working with. Having done that, you can change the overall project tempo and, providing the change isn't too dramatic, you shouldn't hear any significant drop in audio quality. Time-stretching and pitch-shifting are both technologies that involve compromise and while Logic's algorithms work quite well, they're not up there with the best dedicated time-manipulation programs, so don't expect to be able to make radical changes to tempo without some artifacts becoming audible. Usually 10 or even 15 percent will be fine, but aim for a 50-percent change and the sound quality is likely to suffer. Having said that, sometimes you can take liberties with individual notes, such as a bass guitar note that needs extending by maybe half again. The simplest way to do this is to separate the note into its own Region, then use Alt/Drag on the lower right-hand corner of the region to stretch it to a new end position. If only the odd things need fixing, this is often easier than invoking the full Flex Time feature.

Going Griddy

Flex Time is potentially very powerful, and allows us to correct small timing errors or to nudge backing vocals into line with a lead vocal very easily. When you activate the global Flex function and the Flex icon at the header of the audio track you intend to work on, the contents of that track are analysed, and then dotted vertical Transient Markers appear, showing where Flex Time has identified the start of a new note or beat, which it does by looking at both amplitude and pitch. Click on any of these lines and it becomes a solid, active Transient Marker allowing you to drag it left or right to stretch or squeeze the audio between it and the previous or next active Transient Marker. It is important that you click on the Transient Markers either side of the one you are using to make them active, otherwise any stretching you do will affect audio all the way back to the previous active Transient Marker or, if none have been clicked, right the way to the start or end of the region. Should you need to get rid of an active Transient Marker, click on it, then click the cross icon that appears directly above it.

When you activate Flex Time on a track, Logic will analyse that track's content and place Flex Markers on it (the dotted lines). Clicking on those lines activates them, allowing you to stretch and squeeze the audio between them.

Wonderful though Flex Time is, it needs to be used with care as it sometimes identifies transients other than the ones you need to work on, such as treating the pick noise before a guitar note or the breath before a word as a separate event. It is also possible to get too carried away trying to make everything fit neatly onto a grid when the timing 'errors' you see may not be audible or may be part of the essential feel of the performance. Sometimes just correcting four or even two beats to the bar is enough, allowing the notes in between to look after themselves. Also be aware that instruments that slide between pitches, such as fretless bass or slide guitar, are often best timed by ear, not by the grid, as the slide up to a note may, quite legitimately, come before the beat.

Logic's Fade tool lets you speed up or slow down regions to create a convincing 'tape stop' effect.For those things that do need to conform to a grid, you can opt to quantise a Flexed audio region using the usual Quantize parameter in the Inspector, but before you do so, check that it hasn't added any Transient Markers where they don't belong, or you could end up making things sound a lot worse. Similarly, if a note is so badly timed that Quantize nudges it into the wrong time slot, you may have to deal with it manually. Quantising can be useful for tidying up drum loops you've imported that might have a slight swing or groove that doesn't sit correctly with your main drum loop. However, if the main drum loop also has a bit of feel built in, then viewing the two tracks side by side is a better option, as that will allow you to line up the beats manually by moving the Flex markers to match what you see on your main drum part. For simple parts, try the Slicing option to see if it gives you more natural-sounding results than the Mono or Poly modes.

Winding Down

Another often overlooked feature of Logic Pro X is just how simple it is to create a really authentic tape or vinyl 'slowing down' effect — a popular (and sometimes overused) way to create transitions in dance music. To achieve the effect of slowing down or speeding up, use the Fade tool to select the required area of interest, then scoot over to the Region Inspector and you'll find that if you click on Fade In or Fade Out, up pops a choice of Fade In/Speed Up or Fade Out/Slow Down. Pick the speed options rather than the usual fade. Obviously these effects can only be applied to the start or ends of regions, so if you need one in the middle of an audio Region, you'll need to split it into smaller sections so that you can apply the Fade Tool to the area you need. The effect is very authentic, capturing both the timing and pitch changes of the real thing.