Creative Loop Construction

Wilf Smarties explores the never‑ending world of sample loops and how best to use them in your music.

Why use loops at all, why not simply play everything yourself? Using a fragment of somebody else's playing (or even programming) in your composition can quickly inject a feel that is either beyond your own musical or technical resources, or may simply be something that you wouldn't have thought up on your own. For example, if you choose a classic breakbeat, you will probably be accessing sound quality and fidelity from another era, a unique‑sounding drum kit, and perhaps one of the top drummers in history playing at their best. It really can give you a head start when composing or reworking a composition.

Barely a dance track goes by without looped samples being employed somewhere and in some form, whether overtly (as in 1‑bar or 2‑bar patterns) or discreetly (in the form of smaller, less easily distinguished cut‑up fragments). DJs with sampling mixers can capture and hold down a loop on‑the‑fly for mixing into a set, but most musicians use MIDI sequencers and samplers to trigger and repeat loops. Hence samples need not be looped within the sampler itself.

Acquiring The Loops

Without a doubt, the easiest way to get your hands on a decent collection of loops is to choose from the many sample CDs available. If you know a DJ with a decent record collection, you could trawl through that. Otherwise, tune into a dance FM radio station and grab whatever takes your fancy, but keep in mind that you'll have to pay for the use of copyright material if it comes to a commercial release.

Trimming The Loop

Once you've sampled a loop, the next stage is to prepare it for sequencing. If your source was a sample CD, the loop will probably already have been topped and tailed for you. Otherwise, you will need to choose a good start and finish point. This is easiest to do if you can play the loop whilst editing it, and if you have a visual waveform display, this can help too. If your sampler has a 'zoom' function, use it to view the sample start point in more detail for accurate truncating.

Although loops are often trimmed so that they play from the bar start, it is quite common for other positions to be chosen. For example, a pattern with a pick‑up can be truncated to trigger prior to the bar start.

<1...2...3...4.^.>

A loop that's to be used for mainly snare detail may be trimmed to the first snare beat.

<1...^...3...4...>

There are several useful options when it comes to percussion loops. Trimming the end point is not as critical as for the start if you set up your sampler so that loops respond to note length, rather than always play to the sample end. This way you can stop a loop playing simply by lifting your finger off the keyboard, which is useful when a fill or break is coming up.

A constantly looping pattern will need note triggers which pretty much butt join Note‑Offs to succeeding Note‑Ons. To accommodate the vagaries of MIDI, it is worth reducing the full legato value of these by a few ticks.

TIP: Keep one beat more than you actually want to play when trimming the end of your loop sample. This will make tempo adjustment much easier later on.

Tuning The Loop

The obvious thing to do is either (1) write your song at the original tempo of the loop, or (2) tune the loop until it fits the tempo of your song. (There is a third method, which I'll come to in a moment.) Whichever approach you choose, the method is similar: repeatedly trigger the loop in question with a note corresponding to its required play length (1 bar, 2 bars etc). I'd recommend that you use a long sequence to play the loop, since the 'loop' on a sequencer (jumping between two locators) can introduce timing errors. In the case of (1) you will need to tweak the tempo of your track until the loop repeats without a glitch. If you choose method (2), you'll need to use your sampler's coarse and fine tune functions to tweak the speed at which the sample plays. In either case you can tell when the sequence tempo is running slightly faster than the loop, because you will hear the extra beat at the end of your loop (see above 'tip') flamming with the start of the next loop. Just tune out this flam and you should be spot on.

I mentioned method (3) earlier, which is my preferred way of working. Well, if you force all your loops to play at 120bpm (beats per minute), and map them 50 or so to a keyboard, then a single adjustment (ie. altering the tuning of the entire Patch) will bring them into line with any tempo.

Advance And Retard

Now that you've got the loop tuned to run at the desired tempo, it's time to see if it sits nicely on top of a programmed click or kick drum. Run the loop sequence in parallel with a (usually 4/4) metronome. If you are lucky, the pre‑trimmed loop start will lie on a snap value. Otherwise you might find that the loop and metronome are slightly out of alignment. Since you have trimmed the sample to sound right, there's little point in editing the sample start further. Instead, nudge the note trigger backwards or forwards until the pattern sounds coincide with the programmed beat. You can do this one of two ways: (i) either use your sequencer's track or pattern delay to shift the loop sequence relative to the click track, or (ii) move the note trigger away from its current pattern snap value.

Usable Pitch Range

Just because a sample was taken at 90bpm doesn't mean it can't be used at 140bpm. Where do you think all those super‑fast junglist breakbeats came from — sub‑miniature drum kits played by trained mice? Suck it and see. If you want to retain the original pitch of a loop, but want it to play at a different tempo, then time‑stretching the sampled loop might seem to be the way forward. Be cautious — the digital interpolation involved is not particularly good with rhythmic patterns, because of the way the sound is broken down into tiny sections and then reassembled with either some sections repeated or some discarded. Every join is essentially a sample loop point, and the smoothing/zero‑point crossover searching algorithm employed by most samplers works on a join‑by‑join basis. It doesn't understand about long‑range modulation, such as a 4/4 rhythm, so as well as getting a gritty sound, you may also encounter timing problems.

Cut And Paste It

New loops can be created from old ones, simply by re‑ordering elements from the loop sample. For example, you might choose to cut a 1‑bar sample into eight 1/8th bar segments. Once each segment has been trimmed and mapped onto a keyboard patch ready to play at the original pitch, a MIDI sequencer can be used to recreate the loop. Why bother? Well, once you have sliced up the loop, you can re‑order the segments to create entirely new (ie. original) patterns. I'd recommend using a sequencer rather than a sampler/sampling program's native paste routine for this, as it is generally faster, much more flexible, and tighter. You might find the sequenced segments sound better if the tempo is raised slightly above the original, particularly if they have been re‑ordered. This tends to eliminate flams between segment start and end points.

There are now programs designed to take a loop, cut it up into fragments for you, map these fragments onto a patch, and generate a MIDI File which can recreate the original from the segments. I understand Steinberg's ReCycle will do this very nicely for Mac users, but unfortunately I have only an Atari and a PC!

Programming Over The Loop

Train‑spotters can always spot a tried and trusted loop in the mix. For this reason (and others) mix engineers employ various methods to disguise their sources, either by heavy layering of loops, application of effects, or by embedding the loop in the background of a heavily sequenced rhythm track. The latter is probably the best approach to loop customisation, and if it is done well, the feel of the original can be retained while greatly enhancing the sound quality and penetration of the rhythm track.

The most straightforward method, though often the most time‑consuming, is to attempt to recreate the loop pattern using single hits or small loop fragments. If you intend to keep the original loop playing in the background (usually a good idea, as it helps gel the individual hits together), then your quantising template and the loop feel must exactly coincide. This is not so important if the loop is supplying a rhythm that runs across (rather than with) the sequenced drums, where the coincidence of programmed and loop beats is reduced. For example, a hip‑hop loop on a 4/4 programmed beat:

LOOP>> K..KS.K...K.S.K.

PROG>> K...K...K...K...

In the above example, the programmed kick drum and the loop kick drum coincide only on the first beat of the bar. Using a 4/4 loop instead would probably generate kick drum phasing or even flamming problems on the 2nd, 3rd and 4th beats. High‑pass filtering those loops supported by programmed beats helps to reduce low frequency phase cancellation effects. However, where timing differences are causing flams, either the programmed beats will have to be skewed away from a rigid quantise value in favour of the natural loop feel, or the loop will have to be cut into smaller segments and snapped onto the programming.

Groove Templates And Feel

One way to get around the problem of matching the feel of a sample loop to your programmed sounds is to create a quantise 'groove template' for your sequencer, based on the loop timing.

TIP: For this kind of work, choose the highest resolution available to your sequencer.

After getting the loop to run perfectly at the required tempo with no glitches, the next step is to map out a quantise template, usually comprising 16 points to a bar, corresponding to the feel of the loop. This template indicates where programmed beats should be placed to exactly match the feel of the loop. You can actually do this by ear using hard‑edged sounds to help pick out the groove — you can always replace these with more appropriate sounds later. Start by picking out the kick drums with a programmed kick — nudge and tweak them until they feel right. Move onto the snare, then finally the other drum voices. Once you have a programmed pattern that matches the loop, create a groove template using the groove facility in your MIDI sequencer.

Mix engineers employ various methods to disguise their sources, either by heavy layering of loops, application of effects, or by embedding the loop in the background of a heavily sequenced rhythm track.

Other ways of identifying loop accent positions include playing the loop through a signal‑to‑MIDI converter, such as an electronic percussion 'brain', or suitable MIDI drum pad with an audio input. You have to be careful with the sensitivity of the audio‑to‑MIDI trigger (or loop playback level), since the dynamic range of a loop is far, far less than these units were ever designed to handle. The idea is to play the loop through the device while simultaneously recording the MIDI data into your sequencer. Ideally, this should give you an instant quantise template complete with relative note dynamics, but in real life the MIDI output will be a bit messy, and require manual tidying up.

If you have a sophisticated waveform editing program, you may be able to mark the leading edge of individual beats and have them translated into MIDI notes. Programs like Steinberg's ReCycle can automatically do this for you.

If you want to have the advantages of strict tempo quantising (pin‑sharp digital delay patterns, etc), but also want to capture some of the feel and most of the sound of a lively drum loop, you could take a segmented and sequenced recreation of the original loop and simply quantise the MIDI note triggers. As with re‑ordering, you might have to tweak the sequencer's tempo a little higher to lose start/end beat flams.

TIP: In order to prevent overlap between segments (ie. two parts playing at once while the 'baton' is handed over, so to speak), apply legato to the sequencer part to butt‑join the segments (you might want to reduce note lengths by a tiny amount also, to accommodate some of the vagaries of MIDI), and set your sampler's keyboard patch to play monophonically. It helps also to keep sample release times as short as possible — when you release a key you usually want an instant reaction: silence.

Customising Loops

Once you have a matching loop and quantise template, adding in extra beats over the basic pattern should be fairly straightforward.

TIP: When adding extra beats, it is sometimes important that the sound of these beats matches that of the loop, so use individual beats copied from the main loop. It won't matter if the hits are not too clean (for example, a hi‑hat snippet on top of a kick or snare drum), since these sounds are not going to be asked to stand up on their own, merely to play a supporting roll. Also, it's surprising how low in the mix a programmed variation can be used without losing its contribution to the overall feel.

Other tricks include stopping playback of the main loop altogether to make space for a fill, which can be either programmed or consist of a different sample loop (possibly a sample of a real drum fill), or be a variation of the main loop, or any combination of these. If you have followed my preference for loop tuning, and set all loops in your library initially to play at 120bpm, then it is a simple matter to pull up a keyboard patch of fills, tune the patch to your current bpm rate, and toggle through the fills to see which ones fit best.

Onwards And Outwards

Remember: loops need not consist of just drums or percussion — piano breaks, bass lines, guitar parts, vocal acapellas, can all serve to propel a track along. Trimming and tuning techniques are much the same for such loops, although vocals and turntable scratches in particular will seldom trim to an exact snap value, unless you use a MIDI trigger to initiate the sampling process. If you do work this way, you should keep the portion of (hopefully) silence that will be recorded before the wanted signal, and only trim the sample tail.

Time‑stretching is only recommended for samples with few or no sharp transients. Some bass lines and most vocals can take it, at least over a few semitones, before the sound breaks up. Rhythmic samples tend to suffer quite badly after time‑stretching. Otherwise, choose a tempo or key where the key of the loop fits in with that of the music! This limitation has had a distinctive influence on the development of dance music — have you noticed how often musical parts seem to bear only scant harmonic relation to each other? In fact, the decidedly non‑western nature of some of the scales generated by superimposing parts originally from different keys is gradually opening up our perceptions about what sounds 'right' in popular music, to the extent that compositions nowadays often deliberately try to create the effect of a sampled chord being riffed, or of two or more melodies playing simultaneously in different keys. Sometimes art imitates life...