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Flex Time: Using Logic Pro 9's Flex Modes

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Read Time: 4 mins

In a recent tutorial on quantizing audio in Logic Pro 9, we used one of the flex modes so that we could put our audio in time with the new Flex Time feature. But there are several flex modes, and each serves a different purpose — how do you know which one is the right one to use?

Different types of audio need to be processed differently in order to get good results from Flex Time editing, and this is where modes come in. Essentially, they tell Logic what sort of audio it’s dealing with, and how to process it.

Each flex mode has its own set of options. These can be found in the channel strip inspector, just beneath the slice mode itself:


Slicing is great for drums, percussion and other short, transient hits. Logic won’t apply any time compression or expansion to tracks set to Slicing mode. Instead, the audio is sliced at transients, and the transients are shifted. The audio itself stays exactly the same and only the placement is changed. This is the preferred choice for drum tracks, percussion tracks and other percussive unpitched instruments.


Slicing mode provides you with three options to modify in the channel strip inspector. Fill Gaps turns the Decay feature on or off, a feature that prevents noticeable gaps between the sliced sounds, as these can occur when shifting the audio. Decay sets the specific decay time for this feature. Slice Length shortens the slices by the specified amount — if your sliced audio is retaining some of the audio from the following sound that occurs just before the transient hit, this will help fix the problem for you.


Rhythmic mode loops the audio between the transient slices to fill the gaps when it expands material that has a more complicated sonic nature than drums — rhythm guitars and keyboards, and other strummed or chord-based instruments.


This setting’s options are Loop Length, which determines how much of the end of the slice is looped, Decay, which determines how quickly the looped section will fade out, and Loop Offset, which works like slice length and allows you to move the loop area to ensure you don’t catch any of the next sound’s pre-attack.


This setting is designed to be used on tracks that include pitched instruments which do not play more than one note at a time, as opposed to the unpitched percussive instruments that the Slicing mode is used for. You could use monophonic for vocal tracks where there’s only one singer, bass guitar, a violin, synthesizers, and so on.


This mode’s option is Percussive. If this is checked, Logic will preserve the transient hit of the sound to ensure that pitched percussion (such as the glockenspiel) or a percussive string instrument such as slap guitar or pizzicato strings. Leave this unchecked for things like regular violin or wind instruments.


Polyphonic mode allows you to manipulate complex audio where multiple notes are being played at a time, such as guitar, keys, backing vocals, and so on. If there’s a lot going on, then you’ll probably need the advanced algorithms of the Polyphonic mode to handle it.


Use this mode sparingly as it hits the CPU hard. This is reflected in the need for the single setting available for it, Complex, which will enable more transient markers for more complicated audio.


Temophone is a cool way to use Flex Time as an effect. It simulates the way time-stretching has been done traditionally using tape. It’s really only intended to be used as an effect. If you want your time-stretched material to have an older feel, rather than remain accurate to the recording, try this.


The Grain Size setting determines the size of the fragments of audio that are played at normal speed and crossfaded to create the time compression or expansion effect. Crossfade adjusts the length of the aforementioned crossfade (at 0.0, the sound is harder and more abrupt, and at 1.0 it’s smoother and softer).


The speed mode is the traditional effect used to increase or decrease the speed of a track — this means it will change the pitch as well, which is what the other modes have been created to avoid. This is mode is great… if you are a producer of chipmunk songs.

Assigning a Flex Mode to a Track

While we’re here let’s quickly go over how to assign a flex mode to a track. Note that to assign modes, you’ll need to have entered Flex View already (the button is, by default, in the toolbar at the top of the Logic Pro window).

In the Arrange view, the track header has a dropdown under the track name that will say, by default, Off. If you click and hold here, you can change the mode.

Alternatively, head to the channel strip inspector and change the flex mode using the field that says — as you might’ve guessed — Flex Mode.

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