Closing the Loop

By making it possible to freely mix-and-match nearly any repeating rhythmic or melodic passage, loop slicers have changed the way many music professionals work.

Loop-slicing tools such as Ableton Live, Propellerhead ReCycle, and Sonic Foundry Acid have taken the electronic-music world by storm. By making it possible for musicians to freely mix and match nearly any repeating rhythmic or melodic passage, loop slicers have changed the way many music professionals work. Offering a simple building-block approach to audio layering, these programs have also made it possible for countless first-timers to get involved with music production.

In this article, I'll take a close look at these three tools and give some loop-slicing pointers that will apply to other programs as well. You'll find helpful information for acquiring, tweaking, and combining loops of all shapes and sizes.


Before the release of ReCycle and other loop-slicing software in the mid-1990s, matching loops that had different tempos was tremendously time-consuming. Editing and time-aligning individual drum hits, for example, was a slow, painstaking process, even with the most advanced digital audio workstations.

ReCycle was the first program to address that problem and popularize the idea of loop slicing. ReCycle uses transient detection to determine where peaks in an audio file are located. The program looks at amplitude envelopes and seeks out the sudden volume changes that indicate the attack, or beginning, of a drum hit or other note. It then places flags or markers at the beginning of each attack to indicate where the slices are to be made (see Fig. 1).

ReCycle can export each slice as a separate file for playback from any hardware or software sampler. It can also save the slices as a new continuous file at any tempo for layering within an audio sequencer or other audio software.

Sonic Foundry took the ReCycle metaphor to the multitrack level with Acid. Acid was the first audio software to offer both slicing and layering within the same program. The mass-market success of Acid allowed Sonic Foundry to go public and spawned a host of imitators. Ableton Live is another contender and is the best of the post-Acid loop-slicing programs. It's also the only one that works on the Mac as well as Windows.

Later in this article I'll focus on techniques that help make the most of ReCycle, Live, and Acid. But first let's consider some ideas that are applicable to any loop-slicing tool.


In loop sequencing, the process of selection is a central locus of the art. Selection and juxtaposition are everything — all the rest is just craft.

Possible audio sources include the entire universe of sound and everything that vibrates, though you can divide the options into a few practical categories: provided elements, sound libraries, new original recordings, and appropriated elements.

Provided elements

“Provided” elements exist when doing an authorized remix. In such a case, the artist or label will provide you with audio files or tracks on tape. The remixer decides what portions to use. Some producers take an extreme approach, using just the vocals and casting them in an entirely new musical setting.

For the greatest ease in layering and the greatest flexibility when mixing down, use isolated instruments and vocals whenever possible. For example, loops that contain both bass and drums or both vocals and instruments are always harder to match and more problematic to mix down than cleanly separated parts.

If, as is often the case, no audio has been provided, look to the other three categories.

Sound libraries

Prerecorded loops, instrument samples, and effects sounds can be bought as part of a sample library. There are two common types of sample library: audio CD and CD-ROM.

Audio-CD sound libraries can be used with any software or sampler, but the tracks will have to be ripped from the CD and saved, typically as WAV or AIFF files. It will probably also be necessary to edit the loops, because most audio-format libraries put several loops within each track.

CD-ROM sound libraries can spare you some editing; files can just be copied to hard disk. CD-ROM sound libraries are available in a number of formats, including proprietary hardware sample formats. Computer-based musicians who don't use hardware samplers will generally want to stick to the WAV or AIFF collections.

Responding to the popularity of loop sequencing, some firms offer presliced libraries. Sonic Foundry has become a preeminent vendor of canned loops, providing a large line of sound files that are optimized for use in Acid and other programs that support the format (such as Cakewalk Sonar).

Some sound developers have moved to online fulfillment; loops can be previewed, downloaded, and purchased directly from the Web on an as-needed basis at sites such as Sonomic (, PowerFX (, and EastWest Sounds Online (

Before purchasing samples online or buying a library on CD, be certain the audio is in a file format that is compatible with your computer and software, and make sure you understand the licensing terms (see the sidebar “Buyout or Per Use?”).

One downside of using such sounds is that hundreds of other producers may have also bought the same sample libraries. If you care about originality, try to do something with the loop to make it your own. Possible tactics include using signal processing, chopping and rearranging the loop, and replacing sounds with new instruments.

New original recordings

A loop recording session with a live drummer or rhythm section can be wildly fun and rewarding. It's the best way to get all-original loops that are exclusively your own.

Here are some simple rules to ensure optimal results:

Have the drummer play to a click track or metronome so timing is steady.

Do not apply any signal processing (such as delay or reverb). Tracking “dry” gives you more choices later.

If you are recording a rhythm section or full band, put each instrument on a separate track. Once you combine them, it's very difficult to “unmix” them.

Try to put each drum on a separate track when recording drum kits.

Slate your loops. Have the engineer or drummer speak into a mic at the beginning of each take. Be sure that the tempo in the slate is mentioned; for example, “This is rock pattern number 1, 100 bpm, take 2.”

Jot notes on paper about every take, including the tempo, the start and end times, and any other words of description. Paper notes and audible slates make it easier to locate and edit loops after the session.

Leave time at the end of the recording session for transfers. Transferring means converting the audio from one recording medium to another; for example, from 2-inch analog tape to files on hard disk or CD.

Be sure that the transfer is in a format that can be used easily with your setup. Most studios today have CD burners; I always ask for an ISO 9660 (PC-format) CD-ROM of WAV or AIFF files. Such a disc will be compatible with Windows and Macintosh computers.

Appropriated elements

The word sample has come to be synonymous with the reuse of excerpts from other recordings. Appropriating elements from previous works and recasting them in a new work is a timeless artistic and literary strategy, practiced by luminaries such as William Shakespeare, Andy Warhol, and others. That legacy has nothing to do with the music business, which is a highly competitive and litigious arena.

The growing popularity of sampling gave rise to a new music-industry endeavor called sample clearance. To obtain sample clearance means to secure permission to reuse an excerpt of a recording. Although any kind of deal is possible, licensing samples can be expensive. I've heard of extreme cases in which sample owners insisted on taking majority ownership of a new composition.

Nonetheless, if a recording is to be released commercially, the samples should be cleared first. Settling a sample clearance after a song has become a hit can be far more problematic and expensive than getting permission in advance.


Once you've selected audio source material, you'll need to edit the sound files into usable loops. That is best done using professional sound-editing software such as BIAS Peak (Mac) or Sonic Foundry Sound Forge (Win).

Loop files that are edited correctly can be imported or previewed instantly by Acid and Live, which helps speed things along when selecting audio in those programs. Here are some things to bear in mind when editing loops:

  • Cut on the “1,” at the beginning of the first beat in the measure or bar. I always try to cut immediately before the first cycle of the attack (see Fig. 2).
  • Don't cut into the transient! Edit immediately before the attack begins, or else you'll lose some of the instrument's character.
  • Listen to the loop. Most audio-editing programs have a “loop play” or “audition” feature that plays any selection repeatedly.
  • If the loop sounds anything less than slamming, check the start and end points.If the above four tips don't help, and things still sound weak or disjointed, try a different loop. Bands and drummers often make timing errors, so not every recording is loopable.
  • Loop start and end points should always fall on zero crossings. Zero crossings are points at which the waveform is at 0 dB, represented as the line in the middle of a waveform display.
  • As an extra precaution, meticulous producers such as Mark Pistel (Consolidated, Meat Beat Manifesto) always perform a tiny fade-in at the beginning of a loop and a tiny fade-out at the end to force the waveform to zero. That is done while zoomed way in; the fade can occur over a single wave cycle.
  • Make note of the loop's tempo and the number of measures in the loop file name when saving or renaming the file. I like names such as “rockbeat 1 - 110bpm - 4x.WAV” and “reggaepattern2_90bpm_2meas.AIFF.” Loop sequencers will frequently miscalculate the tempo and length of a file if the file is more than one measure long. Having the vital statistics front and center in the file name can save time and prevent confusion when layering loops.


Sonic Foundry's Acidized audio file format and Propellerhead's REX and REX2 formats combine loop audio with the loop tempo and slice-point coordinates. Acid and ReCycle can save loops in these proprietary formats, and you'll find a sizable selection of such loops in sound libraries ready to use.

However, the pressing need for presliced audio libraries has diminished as loop sequencers have evolved. Any WAV file can be imported into Acid and, if correctly edited, will be sliced and time-aligned instantly. Acid can also autopreview loops and play them from the Explorer display at a project's tempo prior to importing. Live's comparable feature, Pre-Listening, plays WAV and AIFF files from the Browser panel also in time with the current session.

To recap, both Acid and Live can use practically any loop without special conversion into a proprietary format. And you don't have to export or save loops in a sliced format if you're only using the loops in a single composition.

The benefit of having preformatted loops comes into play when using a nonslicing sequencer or software sampler. Emagic's Logic, Steinberg's Cubase VST and Cubase SX, MOTU's Digital Performer, and Propellerhead's Reason support the ReCycle REX2 format, as do the Steinberg HALion and Emagic EXS-24 software samplers. These programs will import any file that has been sliced in ReCycle and will handle the slices as a single track or file, allowing free adjustment of the tempo.


Your loop-slicing goal should be to have one note per slice. Slices containing two or more notes (or drum hits) will not time-align correctly, and notes that have been broken into two or more slices won't sound right.

The grid-slicing features of Live and Acid set slice points at predetermined intervals by applying a note-value grid. That is in contrast to the transient-detection method used by ReCycle, discussed later in this article.

In the lower part of the Live display is the Clip view, in which you'll find the Warp settings. One of the Warp settings is a confusingly labeled pull-down menu called Transients (see Fig. 3). That menu is used to set the Transient Resolution (or “Transient Res” in Live 1.x), which applies a grid to the loop. A 1/16 Transient value slices the loop at every 16th note. That default value works fairly well with many typical pop, rock, and dance drum tracks.

The Acid grid setting, named Force Divisions At, is found in the Track Properties display inside the Stretch tab. Force Divisions At also defaults to a 16th-note grid value; it's a fine starting point and can be adjusted using the pull-down menu.

Sixteenth notes may be too small a grid for pitched-instrument loops. Notes held longer than a 16th note will get split up, which can cause audible noise. If slicing makes a loop sound distorted or grainy, try increasing the grid value to eighth or quarter notes.

Conversely, 16th-note grids might be too big for busy loops. If time-shifting causes tempo variances within a loop, try a 32nd-note grid value.

In summary, the default 16th-note grid usually works well for dance-genre drum tracks. Finer grids such as 32nd notes may work better on frenzied percussion parts; larger grids are often needed for pitched melodic parts. Be sure to check the waveform display, look at where slice points are placed, and listen carefully when slicing and time-shifting.


As mentioned earlier, transients are sudden increases in the volume of a waveform that normally happen during the attack or beginning of a drum hit or note. Transient-detection algorithms analyze the waveform and try to find any sudden digressions that might signal an attack.

Drum hits usually have pronounced transients caused by the drumstick displacing the drumhead or cymbal. As a result, accurate transient detection is quite feasible with drum loops. Sustained-pitched musical phrases such as bass, keyboard, or guitar parts can be more difficult to transient detect; legato passages might have few or no detectable transients.

Transient-detection sensitivity can be adjusted in some products. Sensitivity is a “threshold” value — only those volume changes that exceed specified decibel or displacement levels will be flagged as transients.

Sensitivity is a major feature in ReCycle and is easy to use. Click-and-drag on the Sensitivity slider, and slice markers will appear (or disappear) in the waveform overview.

To find the sensitivity setting in Acid, double-click on any clip to open the Track Properties display. Then click on the Stretch tab, in which you'll find the Additional Transient Detection numeric-value field (see Fig. 4). Acid uses a default value of 10 percent sensitivity, but the setting is user-adjustable from 0 to 100 percent.

Because all loops are different, there is no magic setting that will work in every instance. Again, the goal is to have one note per slice and one slice per note. Watch the waveform overview as you boost or cut sensitivity, and you'll be able to get to the optimal number of slices quickly.


As good as these software products are, they still can't do all the work for you. After adjusting grid and sensitivity values, you may still have to add or remove some slices by hand to obtain the one-note, one-slice goal.

In ReCycle, simply click on the Pencil button, which activates the Pen tool. Clicking the Pen tool in the waveform display will create a new slice marker. Markers can be moved to any location within the loop by clicking and dragging on the triangular flag at their top.

In Acid, users will again open the Track Properties display and go into the Stretch tab. Then click with the right mouse button in the waveform display. Selecting Insert Marker from the resulting contextual menu will make a new slice point in the file. Markers can be moved to new positions by clicking and dragging on the brown flag at the top of each marker.

Live uses the concept of Grid markers and Warp markers, which may be slightly counterintuitive for people accustomed to the ReCycle model. Grid markers represent Live's tempo map superimposed over the loop or file. You can assign a grid position to any point within an audio file. Double-clicking on any marker number will turn it into a Warp marker; click-and-drag on Warp markers to move them to any point in the file or loop (see Fig. 5).

When working with Warp markers, begin with the first beat in the loop, and then proceed from left to right. Any markers located to the right of the currently selected Warp marker will shift as the current Warp marker is moved.

Live Warp and Grid markers really come into play with files that contain tempo changes or unsteady playing. You can use Warp markers to fine-tune the groove or to completely disrupt the time flow. Ableton founder and CEO Gerhard Behles says Warp markers were designed to align song-length audio files to the session beat but are often used for other purposes, “like moving beats back and forth in time, by milliseconds or note intervals. We have been surprised by how frequently this method is used,” says Behles.


Acid and Live (version 2) both can optimize the slicing process according to the type of audio. That can have a tremendous impact on the sound quality of the sliced loop.

In Acid, go into the Stretch tab in the Track Properties display:

  • Click on the Stretching Method pull-down menu to select the type of audio you'll be working with.
  • Select Looping Segments when slicing drum tracks or other nonsustaining audio.
  • Choose Nonlooping Segments for sustained phrases, including synth “pads.”
  • Use Pitch Shift Segments to decrease artifacts or distortion that can be caused by pitch-shifting or extreme tempo changes.

In Live 2, check out the Mode menu, which you will find in the Warp section of the Clip view:

  • The Beats setting is the default and is best for drum or percussion loops.
  • The Tones setting is for bass lines, singing, and other monophonic melodies.
  • The Texture setting works well on polyphonic orchestral or band recordings in addition to pads and noisy textures.
  • The Re-Pitch mode stretches both time and pitch, much like changing the speed on a turntable or tape deck.
  • Live Tones and Texture modes have a Grain size setting instead of the Transient parameter. Grain is a type of resolution control, and it determines the size of the data-stream window that is to be processed. Ableton recommends using a smaller Grain setting on monophonic pitched passages and a larger window on complex polyphonic passages; the default values make good starting points. The Texture mode also includes a Flux value that adds a bit of randomization to the result; modest amounts can be beneficial when stretching complex passages.

As Ableton's Behles says, “By choosing the right stretching methods and setting the respective parameters, you will get very good quality even for heavy stretch factors.”


To recap, remember to avoid placing slice markers or edits inside the body of a note, and always cut immediately before the attack.

For pitched, melodic loops, use larger grid settings such as eighth or quarter notes. Make sure that you know how to adjust transient-detection sensitivity and how to add, move, or remove slices by hand.

Acquaint yourself with advanced controls such as Acid's Stretching Methods and Live's Warp modes. Use these optimization features anytime you're slicing a pitched or melodic part.

Start using these simple techniques and you'll be well on your way to having great-sounding sliced loops.

Todd Souvignieris the author of The Musician's Guide to the Internet, 2nd ed. (Hal Leonard, 2002), and the forthcoming Loops & Grooves: The Musician's Guide to Groove Machines and Loop Sequencers (Hal Leonard, 2003). Visit Todd online at


Sound libraries are marketed under two different licensing models: buyout and per-use.

Per-use or “needle-drop” sound libraries require payment of a license fee or “royalty” for each use of a recording. Each subsequent usage increases the cost of a per-use library. Depending on the library and usage, this fee may be cheap or expensive. Better-organized per-use libraries include forms for notifying the licensor and remitting the appropriate fees.

Buyout sound libraries take the opposite approach and have become the more common model. A one-time up-front license fee is included in the purchase price of the library. Sounds purchased can then be used in practically any production, with no additional fees or paperwork. Some sound developers use the phrase “royalty free” when advertising their samples. “Royalty free” is just marketingspeak for “buyout.”

Buyout libraries may be more costly to acquire initially than per-use libraries. But over the course of time and usage, a buyout library may actually be less expensive and more convenient.