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Creating files that can stretch to the project tempo doesn’t have to be difficult


By Craig Anderton


Sonar was the first program after Sony Acid itself to allow turning standard WAV files into the “Acidized” format. This format adds metadata to the file that indicates where transients exist, and links these to tempo so that the file can “stretch” to accommodate tempos other than the tempo at which it was recorded. For example, you could drop a two-measure Acidized loop that was recorded at 120BPM into a project with a tempo of 140BPM, and the file will be shortened intelligently so that it lasts two measures at the faster tempo.

Although Acidizing a file so it stretches over a wide range of tempos can be difficult with complex material, with simple rhythmic loops you can “Acidize” the file in a few easy steps if you’re primarily interested in speeding up rather than slowing down the tempo. That’s because it’s much more difficult to add material to a file so that it’s longer (the additional material has to be synthesized), compared to removing material to make it shorter, as is needed with a faster tempo.

1 LoopConstruction.jpg

Fig. 1: Open the Loop Construction window.


Begin by double-clicking on the file to be stretched, as this opens the Loop Construction window.

2 Beats in clip.jpg

Fig. 2: Click the Enable Looping button.


Next, click the Enable Looping button. Sonar estimates the number of beats in the file; if correct, the Orig. BPM field displays the original tempo. If not, enter the correct number of beats in the Beats in Clip field.

3 Transient Detect.jpg

Fig. 3: Transient detection is an essential part of the Acidization process.


For Transient Detect, enter 0 and hit Return. The transient markers that control slicing will jump to the value in the Slices field.

4 Slices.jpg

Fig. 4: The Slices field lets you choose a rhythmic value that’s most compatible with the part.


In the Slices field, choose the rhythmic value that matches the pattern (e.g., with a 16th note-based pattern, choose 16th notes).

5 Add Marker.jpg

Fig. 5: You can add markers for any transients that Sonar misses.


Sonar detects transients automatically, but the process isn’t perfect. Acidization works best if there’s a transient marker on every transient, so if a beat doesn’t have a transient marker (like a 32nd note accent in a 16th note pattern), add a marker in the strip with the other marker triangles by double-clicking above the transient.

6 Erase Marker.jpg

Fig. 6: You can also remove transient markers if there isn’t really a transient.


If there’s an unneeded transient marker (e.g., in the middle of a sustained eighth note cymbal crash where nothing happens underneath it), remove the marker by clicking on the Erase tool, then clicking on the marker you want to remove.

Note that with many patterns—especially those generated by a drum machine or step sequencer—you probably won’t need to add or subtract transients, as 16th note slicing will work more often than not. Also note that if the drum pattern was played by a human, transients likely won’t fall right on the beat. Move them to line up with the transient start by clicking on the red triangle and dragging.

7 Set pitch.jpg

Fig. 7: You can also have the file follow the project pitch.


If the material is pitched (e.g., synth arpeggiation), click the Follow Project Pitch button and select the file’s original key from the drop-down menu. With unpitched material, leave this field grayed-out.

8 Save File.jpg

Fig. 8: Save the file once it’s Acidized properly.


Now it’s time to save the file. Click on the floppy disk button; the file will contain the additional stretching metadata. You can also save the file simply by dragging the clip to the desktop, but hold down the mouse button until the file is finished copying.

By the way, if you’re creating a file from scratch that you want to stretch, choose a slow tempo, like 60 to 90BPM. As mentioned at the beginning, tempo-stretching works better for speeding up than slowing down.


CraigGuitarVertical.jpgCraig Anderton is Editor Emeritus of Harmony Central. He has played on, mixed, or produced over 20 major label releases (as well as mastered over a hundred tracks for various musicians), and written over a thousand articles for magazines like Guitar Player, Keyboard, Sound on Sound (UK), and Sound + Recording (Germany). He has also lectured on technology and the arts in 38 states, 10 countries, and three languages.

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