Sync your MIDI Sequences To Pre-recorded Audio Tracks

Logic Notes

Published in SOS April 2002
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Technique : Logic Notes

This month we show you how to sync your MIDI sequences to audio tracks you've already recorded. Also, there's a trick for replacing live drum parts with samples, plus a cluster of practical tips to get Logic working better for you.

Synchronising live performances with sequenced parts can be a difficult task. Most people do it the easy way -- setting up a guide sequence and then recording the live parts in time with this. However, there are occasions when it's necessary to attempt the more difficult method of sync'ing your sequenced tracks to audio which you've already recorded. If you had to do this by hand, it would involve programming a click into your sequencer and then laboriously tweaking the tempo of each bar so that the click stayed in time.

You'll be glad to know, then, that Emagic have provided a Reclock Song function which makes this job much less of a headache. All you have to do is record MIDI notes in time with the au

Current Versions*     PC: Logic Audio Platinum v5.0.0. Mac: Logic Audio Platinum v5.0.0.

dio, and then Logic inserts a bunch of tempo changes to make the bars and beats fit the placement of these notes.

The first thing you have to do is import your recorded audio into an audio track in Logic. Then you should set up a MIDI track and route the MIDI output of a master keyboard or drum pad to it, in order to create a MIDI guide recording for the Reclock Song algorithm. If you have no way of inputting MIDI notes from an external unit, then you can always create a new Keyboard object in the Environment and use that -- you don't need to cable it anywhere, as it is routed to the sequencer input by default.

Once this is set up, you should record the output of your MIDI device while you're playing along with the audio recording. I find that I get the smoothest results by recording one note at the beginning of each bar. This means that the tempo will only be changed by Logic once per bar, and I find that

Replacing Live Kick & Snare Parts With Samples     In order to get a more consistent sound, some mix engineers use the kick or snare tracks in a multitrack drum recording to trigger samples. Once upon a time, you had to use a high-end digital delay or a dedicated drum trigger module, and it's not immediately obvious how to achieve the same effect in Logic. However, the Sample Edit window's Audio To Score function provides a workaround which can produce quite workable results. Let's say you're replacing the snare track. Double-click on its object in the Arrange window to open up the Sample Edit window, and choose Audio To Score from the Factory menu. This brings up a little floating settings window, and graphs appear under the audio waveform with little lines showing where trigger points are being detected. You're aiming to get one of these lines per drum hit on the track. The way I do this is to set all the parameters to their minimum value, with the exception of Smooth Release, which I set to 10 percent, and Quality, which I set to High. These settings will produce a swathe of extraneous trigger points. The first way to reduce the number of these is to increase the Threshold as far as possible, but without causing the algorithm to completely miss any of the hits. This should weed out any trigger points generated by spill from other drums, but you may still get clusters of trigger points where you only want one. To tidy these up, slowly increase both the Granulation and Attack Range parameters, but only as far as is absolutely necessary, because these parameters can interfere with the timing accuracy. Once you've whittled it down to only one trigger point per drum hit, pressing the Process button generates a MIDI object on the same track as the audio (you may need to drag the audio aside to find it) which you can use to trigger your replacement sample. However, the Audio To Score function can produce a variety of different pitches and MIDI channels, so you may have to use the Transform window to fix all the notes to the pitch and channel you want. Also, it's worth experimenting with the MIDI sequence's Delay parameter to compensate for any delay inherent in the triggering process.

this avoids 'lumpiness' in the rhythm from beat to beat. However, if there is a lot of tempo variation, you might find that playing one note per beat will work better.

It's definitely worth spending a bit of time getting the MIDI notes as close as you can, but it's pretty difficult to get them all bang on, so it's fairly likely you'll need to edit their positions after you've recorded them all. Though it's vital that the MIDI notes are well in time with the audio, it is a rather tedious process going through and tweaking errant notes into line. However, here are a few ways I keep the time spent in 'timing purgatory' to a minimum.

Firstly, I make sure that I have a few useful key commands at the ready: the ones that are particularly handy here are Merge Objects, Play, Stop, Split Objects By Song Position, Goto Marker Number 1, Nudge Event Position By Tick -1 and Nudge Event Position By Tick +1. Select all the MIDI objects you've recorded and Merge Objects. When you've done this, use the new merged object to trigger a fast-attack sound, such as a click, alongside the audio.

Now, with the MIDI object selected, play the Song from the beginning. Every time you hear a click which is out of time, quickly hit Split Objects By Song Position before the next click sounds. When you've reached the end of the Song, you should have a number of MIDI objects, and each one of these will have a final note which is out of time.

Create a single Marker point and then open a floating Marker List window -- both of these can be done from the Marker submenu of the main Options menu -- and resize the floating window so that it shows just the information for the one Marker. You can use this Marker to locate the Song Position Line quickly, and you can easily move the Marker around the Song by dragging on the bar number in the floating window.

To start with, move the Marker to about four bars before the end of the first MIDI object. Next, use the Key Commands to play from the marker, and to split the object again to isolate the offending note. Having just heard the timing again, you ought to have some idea of whether the note needs shifting early or

Logic Tips     It's worth being aware that the Lookahead parameter within Logic's built-in Noise Gate and Enveloper plug-ins introduces a delay in the signal path. However, unlike the normal plug-in processing delays, this isn't corrected by Logic's automatic plug-in delay compensation. The Enverb plug-in can create some great metallic drones if you set Hold to a few hundred milliseconds and keep Density down to a few percent -- this works particularly well when you feed it with full mixes. Preceding the Enverb with one of the equaliser plug-ins gives you a lot of control over the sound of the drones, while a compressor following it can help smooth things out a bit, to make the sound more pad-like. If you find yourself reaching for the Crescendo preset from the Function menu's Transform submenu, try changing the Crescendo operation to Exponent. The little graph at the bottom of the window will show the curve, and I find an exponent value of about 2.5 provides a nice alternative to the normal linear velocity increase. You can sometimes see clicks in an audio recording as spikes on the waveform when you look at it in the Sample Edit window. In such cases, you can often reduce the effect of the click by selecting the area of audio with the spike in it and then redrawing the waveform, using the Sample Edit window's Pencil tool, to remove the spike.

late, and you can shift its object by highlighting it and using whichever of the two Nudge Key Commands is required. To listen to the effects of your changes, simply play again from the Marker.

Once you've worked through all the dodgy notes in this way (saving the Song regularly as you go!), select the whole track and Merge Objects. Have another listen through and split the object again if you hear any other errant notes you missed first time -- they'll be more obvious now that everything else is pretty tight. Tighten those up, Merge Objects once more, and then you're ready to use the Reclock Song window, which can be opened from the Tempo submenu of the main Options menu.

In the Reclock Song window, you'll need to make sure that only the top two boxes are checked -- Use Guide Sequence and Create Tempo Changes To Preserve Timing. The Left Destination field shows the bar to which the first MIDI note will apply, and it's sensible to set this to be bar five or so, so that you have a little space at the beginning of the Song before the audio starts. Finally, select the step increment which corresponds to the number of MIDI notes you have recorded per bar of the audio -- if you followed my advice to put one note per bar, then you'll want to select '/1' -- and press the Reclock button.

Logic will now generate the tempo changes required to put your MIDI notes onto the beat. There are a couple of things still to mention, though, before you start layering MIDI parts over the audio. The first is that Logic on my particular machine gets a bit spooked by the Reclock procedure, such that it sometimes seems not to have worked properly. However, I find that this sorts itself out if you simply save the Song, then close and reopen it -- weird, I know, but effective nonetheless.

Also, make sure that you only press the Reclock Song button once. If you press it twice, the timing will end up all wrong. Given that this is the case, you'd be forgiven for wondering how you go about 're-reclocking' the Song, should you decide that you want to refine the timing of the MIDI notes and revise the tempo changes accordingly. And what if you want to use more notes per bar just for one section, for a slowing-down ending perhaps? These questions and more will be answered here soon, so keep your eyes peeled...