LOGIC NOTES

How to match your song's tempo automatically to that of a sampled loop

Published in SOS October 2001
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Technique : Logic Notes

Tweak the levels of individual sounds in a stereo mix, and learn how to match your song's tempo automatically to that of a sampled loop. Plus, the usual fistful of handy tips, including some ways to make your life easier using Logic's colouring options.

Something we regularly get asked is whether there's any way to remove the lead vocal from a stereo audio file. Well, the simple answer is that it's rarely (if ever) possible to do this completely, though there is a way in Logic to reduce its level enough to make the file usable. And the technique which I'm going to show you also has a number of more powerful applications as well...

First, make sure that the track in your Arrange window which is playing back your stereo file has a stereo Audio object assigned to it. From the Environment window, assign one of the sends on this object to a spare effects buss, and set this send to unity gain. Then configure the buss in question to be mono, using the button at the bottom left-hand corner of its Audio object, and insert a Gainer plug-in to invert the phase of the buss signal.

If you now press play, the mono buss will cancel out all the mono elements in the stereo file, and you therefore ought to hear that the entire centre of the stereo soundstage has been removed. If you're processing a typical pop mix, then this will typically remove the kick, snare, bass and lead vocal from the mix. You may still hear ghostly remnants of these sounds, but this will probably be a result of any uncorrelated stereo effects (such as most reverbs) which were applied to them.

Such extreme centre cancellation can occasionally be useful in its own right, though it can be toned down by simply pulling back the mono buss fader. However, most people seem to want only to eliminate one of the elements at the centre of the stereo image — for example, only the vocals, or only the bass. If you want to remove the vocals, but leave the bass, try using a Low Cut plug-in after the Gainer. Experiment with the Frequency parameter to get the best results, and if you want a steeper filter slope then insert a second Low Cut plug-in into the chain with the same Frequency parameter setting. The cancellation of the vocal won't be perfect, because the filters will affect frequencies well above their turnover point and will hence slightly reduce the effectiveness of the centre cancellation in the vocal range. Moreover, you will still remove other centre-panned elements, such as the snare drum, which occupy the vocal range.

Similarly, you can often successfully eliminate the bass from a mix using a High Cut plug-in. Bear in mind, though, that bass sounds which are rich in harmonics — many synth basses, for example, as well as fuzz bass or any bass guitar that has a 'honky' sound — will be very difficult to eliminate without seriously affecting upper frequencies as well. And, of course, even if your bass sound is quite dull, you will almost certainly remove the kick drum sound as well.

If you're not getting a good enough result using simple high-cut and low-cut filters, you should try using more accurate frequency-shaping tools instead, such as the Silver EQ or Fat EQ plug-ins. Simply apply cut in any frequency ranges you want left remaining, and also experiment with the overall mono buss level. In this way, you can not only drastically reduce the level of given centre-panned musical elements, but you can also implement much more subtle tonal changes in the centre of the stereo image.

Though the cancellation facilities offered by this simple technique are powerful in their own right, you can also reverse the effect with worthwhile results. By switching the Gainer plug-in out of phase-invert mode, the mono buss can be used to increase the levels of centre-panned instruments, rather than reducing them.

For example, let's say you want to use a stereo drum loop in your track, but the kick and snare aren't loud enough for your taste. Start with the mono buss fader down all the way, and then fade it up a little at a time until you achieve the required change — the hi-hat, cymbals, and toms (which are typically panned off-centre) will be boosted less than the centre-panned kick and snare. The side effect of this, of course, will be that the stereo image width will be narrowed, but this shouldn't cause too many problems if you're only adding a modest amount of extra mono.

For more control over the elements you're boosting, EQ the mono buss to isolate them. In the above example, a Low Cut plug-in would help to isolate the snare in the mono buss, allowing you to independently tweak its level. It can help to solo the mono buss while you're EQ'ing it, so that you can easily hear which frequencies you'll be adding. And remember, just as when using any other effect, make sure you bypass the processing by muting the mono buss every now and then, to make sure that you're really making an improvement. A word of warning here, though: given that adding extra mono elements will not only change the instrumental balance, but will also increase the overall playback level, beware of confusing 'louder' with 'better'.

Another application of this technique is in increasing the level of the lead vocal in a finished mix — just EQ the mono buss to isolate important vocal frequencies, and add a little to the stereo mix. In fact, mastering engineers have been using a technique similar to this for years.

Once you've got to grips with the idea of using a mono buss for cancellation and reinforcement, allowing you to alter the tonal balance of the centre-panned instruments in a mix, you might also want to try the following extra trick. Let's say you're using the mono buss to alter the tone of the snare drum, but this is also affecting that frequency region of the lead vocal's timbre in an undesirable way. One way around this problem might be to insert a Noise Gate plug-in into the mono buss (whether you're using it for cancellation or reinforcement), and use the side-chain filters to get it triggering only on the snare drum. This way, the mono signal will only alter the tone of the centre of the stereo image during snare hits. You may need to tweak the time settings of the gate plug-in to get the best result, but this technique can be the next best thing to travelling back in time and tweaking the snare track's mixdown EQ.

There is, of course, the likelihood that the gate in this example will trigger incorrectly every now and again, so you may want to duck the mono buss with Logic's automation in order to compensate for this. In fact, you could perform the gating action itself using the channel automation if you wanted to get really in-depth. While this would be indescribably tedious for a whole track full of snare drum hits, it's much more practical for more isolated sonic troubleshooting — fancy de-essing that lead vocal a little? Mike Senior.

Matching Your Song Tempo To A Sampled Loop     So you've created a great sample loop, or you've found one on a sample CD, and now you want to use Logic to sequence some MIDI parts alongside it in order to start building up a track. The first thing you'll have to do is get the song running to the tempo of the loop. This can be a hassle using a hardware sampler, but if you have the facilities to import your sample into Logic's Audio Window then the tempo can be matched in an instant. All you have to do is drag your loop onto a track in the Arrange window, set the left and right locators in Logic's Transport window to encompass the number of bars in the loop, highlight the audio region and press the 'T' key. By default, this triggers the Adjust Tempo Using Object Length And Locators function. Hit Return to select 'Globally' from the subsequent dialogue box, and the tempo will immediately be set to perfection. Mike Senior

Make Things Easier By Using Colours     Colouring your audio and MIDI regions in the Arrange window can really help to avoid confusion when comping or when working with a very complex arrangement. To set the region's colour, highlight it, select Object Colours from the window's View menu, and then pick a shade. Colour can make things clearer in the Environment window too, and the procedure for setting an Environment object's colour is exactly the same. What's more, colour can actually make your life easier whenever you find yourself repeatedly having to highlight only some of the regions within an track — it is tedious to have to hold shift and click seventeen times every time you want to carry out an operation on that group of objects. However, if you colour them all the same then next time you want to select them all, you only have to use the Select Equal Coloured Objects option in the Edit menu. Seeing as this option is also available in the Key Commands window, you can even speed up this action, if you need to use it a lot. Mike Senior

Logic Tips     There are lots of occasions where you might want to compress or equalise several audio tracks together. To do this, change the output assignment field on each of their audio objects so that they all feed a spare effects buss directly. Then insert the required effects plug-in on the buss Audio object. Mike Senior There are such a lot of Key Commands available in Logic, you'd be forgiven for forgetting a few of them. However, you can create a list for ready reference. Select Copy Key Commands To Clipboard from the Key Commands window's Option menu, and then paste the list into your choice of word processor. All you have to do then is adjust the tab stops to taste and print off a copy. Mike Senior If the cabling in the Environment window is getting in the way, then deselect the Cables option in the View menu. And, don't worry, this won't actually remove the cabling. It will hide it from view, but all the MIDI routing it represents will remain intact. Sam Inglis As you may know, dragging from left to right within the time bar at the top of the Arrange window quickly sets up a playback loop. However, if you drag from right to left, this causes playback to skip the selected section, rather than looping it. This way you can, for example, try out a version of a song with one less chorus before going through the hassle of the actual editing. Mike Senior