Drum Editing & Replacement In Logic Pro

You're given a Logic project with a less than impressive drum recording, and you need to make it sparkle. Do you book another recording session, get down to some serious editing, or replace the whole lot with samples? Delay your decision until you've read this.

Trimming your tracks is the first step when editing drums. Strip Silence, shown here, makes this task simple, though you may have to experiment with the parameters to achieve the best results. One of the major disappointments in the release of Logic 8 was the lack of anything to let users automate the often tedious process of editing drum and percussion parts. Many of Logic's competitors have featured such capabilities for a while: Pro Tools has the well-respected Beat Detective and Sonar's AudioSnap facility seems to be a powerful tool. Beat Detective can detect transients and split audio 'on the beat', so you can quantise, move and experiment with percussive elements to your heart's content. If you want to learn more, Simon Price's article, published in SOS August 2003 (which shows you how long Pro Tools has been ahead of Logic in this area) and on-line at www.soundonsound.com/sos/ aug03/articles/protoolsnotes.htm, will give you a decent overview of the whole process.

When I get into discussions about drum editing, musicians will often respond with statements along the lines of "Why not just get the drummer to play properly?", and this is a fair point. But while this would be ideal, it's not always possible to achieve. For example, if you're a mix engineer, you'll probably have had no input into the recording process itself, so editing (or even replacement) may be the only option.

Getting Started

It is very often the case that recordings of drums occupy multiple tracks, and these need to be kept perfectly locked in sync. This, of course, makes editing more complicated, as you usually only work on a single track at a time. Logic has always had a few tools available to make drum editing easier. For example, you can use the Group feature to make sure that Regions are all cut at the same place when slicing, and that they stay in time when dragging them around.

The first step to drum editing is to cut your drum recordings so that you can easily drag individual hits — samples if you like — around the time grid. There are a number of ways to do this in Logic 8, all of which require a fair amount of manual work. But put some effort in, and you can get pretty convincing results.

As with many other manual editing jobs, it's probably best to work on copies of a Project or audio files, so you can easily revert to a former version that you know you're happy with, if necessary.

Strip Silence

If you look at the waveform of a drum or percussion recording, you'll notice that it features fast transients, and it's the detection and manipulation of these that is key to successful drum editing. Logic's Strip Silence feature is designed to split an audio recording into separate Regions, removing the silence between segments of 'non silence'. By adjusting the Threshold, you define the level of what is considered silence. Obviously, you can also use it to detect drum hits in a Region, and remove any spill that may be on the individual tracks — when a close-miked drum isn't being played, for example.

The main objective when using Strip Silence on drums is to make sure that, when your regions are dragged on Logic's time grid (for example, to the first beat of a bar), the drum sound is heard immediately. To ensure you achieve clean cuts, Strip Silence has a pre-attack setting which, with drums, needs to be kept short, as you don't want to add any dead space to the Region just before the transient.

Logic 8 brought with it a new implementation of the Marquee tool. With new key commands (shown here), you can move the start and end of the Marquee area to the nearest transient, letting you navigate your drum tracks more easily. Using the Select Next Region, Set Locators by Playhead and Goto Left Locator key commands, you can quite swiftly chop up grouped multitrack drums using as a guide a single file (the snare in this case) that you have either processed using Strip Silence, or manually spliced using conventional tools, such as the Marquee tool. Actually applying the process (which is destructive but can be undone) to your files is pretty easy; you just select the required audio Region and choose Strip Silence from the Arrange page's Audio menu.

Once you've set your parameters and clicked on OK, Logic will place the generated Regions onto the Track. If you then zoom in on the Arrange page, you can see exactly what the process has done to your audio. As I've mentioned, you can undo the process if it's not what you intended, or further edit the Regions manually.

Strip Silence's main limitation is that it only works on one track at a time, and you cannot zoom the waveform viewing window. So it's impossible to see precisely where the split points are being set, unless you take the extra time to cut the Region into smaller parts and process them one-by-one. In spite of this, Strip Silence is still an extremely useful tool to use in many situations.

Do More With Marquee!

Another method of cutting up drums was made possible with the release of Logic 8. A new implementation for the Marquee tool allows you to use key commands to move the start and end of the Marquee selection to the nearest transient. This is useful, as you can quickly navigate through your drum tracks hit-by-hit.

It works like this: first, set up the key commands to select the start and end of the next transient (their full titles are shown in the screenshot, top). Then select the Marquee tool and drag a box around the Region somewhere near the transients you want to isolate. Use your newly assigned key commands to move the start and end of the Marquee selection to the required transients. Press Esc twice to return to the Arrow tool and click to split the Region at the transient. Alternatively, you can set up the Marquee tool as your second tool from the new Tool setup pull-down menu at the top right of the Arrange page. You can then easily select the Marquee tool by the simple expedient of holding down the Apple key, and get the Arrow tool back when you release the modifier.

While this is a great improvement over what was offered in earlier versions, Pro Tools has a 'Tab to Transient' feature (you simply hit the Tab key to jump to the next transient) which, if included in a forthcoming Logic update, would speed up the whole editing process considerably.

Edit All Areas

Once you've chopped up your audio recording using one of the above methods, you can split any other Regions that are part of your drum recording at these new 'guide' Region boundaries. In this example, I've used the snare transients as the guide. First, you need to select all the tracks you want to manipulate and assign them to a Group — but don't add the track that you've just chopped into separate Regions.

Select the track that contains the split Regions and use the Select next Region, Set Locators by Regions and Goto Left Locator key commands to move the Playhead (referred to as the SPL or Song Position Line before Logic 8) to the start of each of the newly split Regions. If you then click on one of the Regions that are assigned to the Group, that will select them all and you can use the Split Regions at Playhead key command to cut all the Regions in that Group. Once all your tracks are sliced as required you can group them to make sure they stay together when you move or quantise them — but don't forget to add the guide Regions to the Group as well.

Quantising Drum Tracks

Once you have the tracks split at the transients, you can either move the Regions to where you want them to be on the timeline using the usual copy and paste techniques, or you can quantise them by selecting them in the Arrange page and opening the Event editor from the main Window menu. Here, you can set the required value and then quantise the Regions as if they were MIDI data. Of course, quantising will only work if your recording has some kind of tempo map assigned to it. If it was played to a click you'll only need to know the bpm values and any tempo changes — which can then be inserted using the Tempo list in the Tempo section of the Options menu or the Tempo Global track.

If the recording was played 'free', you can try to create a tempo map using the techniques described in the SOS May 2006 article on tempo matching (on-line at www.soundonsound.com/sos/may06/articles/logictech_0506.htm).

Drum Replacement

The Event List enables you to 'quantise' your audio regions, just as you can with MIDI. Providing you have cut your drum tracks so that there is no dead space before the first transient, this should lock your edited drums to the project's tempo. Of course, once you have sliced your beats, individual drum hits can be replaced with samples, a common trick that many producers and remixers use these days. There are some third-party drum-replacement solutions available for Logic, such as Drumagog (www.drumagog.com), but there's quite a lot you can do using the tools available within Logic itself. The aim with drum replacement in Logic is to generate a MIDI Region containing notes that mirror the desired transients in the recording. It's usually done with bass and snare drums, but I know a few brave souls who replace hi-hats too. To do this, we need to use Logic's Audio To Score feature, which is located in the Factory menu of the Sample editor. If you just open a recording and apply this process you're likely to be pretty disappointed. Like most of these analysis procedures, the old tenet 'garbage in, garbage out' applies, and you'll need to do some pre-processing before you'll get the results you want. I tend to make a copy of the drum parts I want to work on and paste them past the end of the Song, or into a new Project entirely. I do this by using the Export As Audio Files feature, which is accessed by right- or Control-clicking on the Region in the Arrange page. By doing this you can be sure you don't damage the original recordings, as it's likely you may have to do some destructive processing on the audio.

Transient Designer

To produce the best source material for turning your audio into MIDI data (which you can then use to trigger a drum instrument or sampler), you need to make the transients as clear as possible, while suppressing the sounds you don't want to hear. Audio quality isn't an issue; you're not going to use these recordings in the final mix; they are purely being used to generate data for the Audio to Score feature. For this example, I'm going to use a recording of a snare. As with most of my recordings, there's a lot of bleed from the other drums in the kit, so the first thing to do is use a noise gate. Logic's basic noise gate is perfect for this, as not only does it have controls for setting the threshold, attack and release parameters, it also allows you to set the frequency range to which the gate will respond. I sometimes place a flat EQ with the Analyser switched on, or the Multimeter plug-in, before the gate, so I can see which are the dominant frequencies of the transients I'm interested in, and then insert these values. You can usually home in pretty accurately on the drum you're trying to isolate. If the beats vary a lot in dynamic range, you can add Logic's Compressor and Limiter to bring them all up to the same level. When you're happy you've isolated your beats, you can then Export the processed recording as an Audio file, by right- or Control-clicking on the Region and then re-importing the processed file back into the Project.

Audio To Score

Once the processed file is back on the Arrange page, double-click on the Region and open it in the Sample Editor. If you've been successful, the waveform should just show the transients you want, with near-silence between them. When Logic performs its MIDI note extraction it will place the Region generated on the currently selected track, which can cause a bit of head scratching if you're not expecting it. I usually create an Instrument track beneath the one the processed file is on and insert the plug-in that will play the replacement sound — in this example, I'm using Ultrabeat.

Drum replacement: this screenshot shows the original audio file for the snare track (top), the file that was created to highlight only the transients (middle), and the MIDI region that was created after using Logic's Audio to Score feature which, in this example, is being used to trigger Ultrabeat. The Piano Roll at the bottom of the image shows the MIDI data in more detail. When you open the Audio To Score window from the Sample Editor's Factory menu you'll see some presets in a pull-down menu. These are a good place to start, but it's likely you'll need to try the process several times with different parameters to generate the results you want. The undo function, and trial and error, are invaluable here.

The Granulation parameter sets the time span of the louder parts and thus the transients. Start with values between 50 and 200 ms and use a short attack time (between four and 40 ms) and short release time (zero to five percent). Leave the Velocity threshold at '1' and set the Basis Quantise to the most sensible value for the material you're using — perhaps 1/4 for bass drum, for example.

Now click on Process. Logic will show a 'sample being processed' display, and a MIDI Region containing the extracted notes will be generated. If you double-click on it to open it in the Piano roll (formerly Matrix) editor, you'll see the individual notes. If the Audio To Score's settings were good, you'll just have notes that fall at the same position as the transients in the original recording. Of course, it's more likely that some spurious data will also have been generated, so you can either edit it out manually or click undo and try changing the parameters.

You'll probably have to drag all the hits to the correct note on which your replacement sample is assigned. To do this, use Select All from the Edit menu and drag the whole lot to the correct note. If you try playing the generated MIDI data and the processed audio together you'll quickly hear and see if Logic has added any notes you don't need. Once you're happy with the MIDI Region, you can copy it to the correct place in the timeline of the original Project. Have a listen to the unprocessed audio recording and the MIDI Region together to make sure they sound satisfactory.

Conclusion

Drum editing and replacement can either be used as creative tools or for improving a recording. The purists may complain, but the listening public are becoming less tolerant of timing errors in their recordings, and even acoustic music can benefit from a bit of editing. Saying this, I wouldn't like to be the person who performs drum replacement or editing on any upcoming remixes of classic Led Zeppelin tunes!