Week #161: SONAR Audio Stretching Options Explained
 
There are five ways that SONAR can stretch audio Clips to conform to tempos other than the ones at which the clps were recorded—but it’s crucial to choose the right tool for the right job.
 
AudioSnap
This was SONAR’s answer to Pro Tools’ Beat Detective, although AudioSnap has other talents as well. It works best with the kind of material that would also work well with REX files, i.e., tracks with percussive transients like drums, percussion, bass, rhythm guitar, non-legato leads, etc. My main use of AudioSnap is to quantize audio clips to a grid, and for this application, it works very well provided that a) you remove transients that aren’t needed, and b) add transients that are needed. This takes anywhere from a few seconds to a few minutes, depending on the size of the clip.
 
Using AudioSnap with program material is possible, but there are better alternatives…keep reading.
 
Groove Clips
This is the best solution where you need a clip to follow tempo and/or key changes, or want to be able to bring a loop quickly and easily into a project with a different tempo compared to the clip’s native tempo. Note that the Browser has an option to audition the Groove Clip at the host tempo so you can evaluate whether the fidelity is suitable for the amount you want to stretch.
 
Limitations: 

• You can speed up Groove Clips (often 150% and beyond) and they’ll still sound good, but you’ll hear artifacts when slowing down much more than 5-10%.
• Libraries with Groove Clips (“Acidized” files) sometimes aren’t edited very carefully, so you’ll think they don’t stretch well—even though they often will if you take the time and effort to open the clip in the Loop Construction view, and edit where the transient markers fall.
• The technology works best with short clips. You wouldn’t want to use it to stretch a two-minute song, nor can you past 128 beats.
• When you convert a clip to a Groove Clip, SONAR makes a guess about how best to stretch it. Sometimes it’s off and you need to enter the number of beats in the clip manually.

 
DSP Stretching
This is the best general option. It works well for program material or individual clips. For example suppose you have a 4-bar loop recorded at 120 BPM and you want to stretch it to fit in a song that’s 110 BPM, so the loop needs to be longer. While holding Ctrl+Shift, click and drag the end so the clip lasts four measures in the song with the tempo of 110 BPM. Note that you can even apply this to a Region FX Clip, although I don’t think this uses Melodyne’s algorithms.
 
Limitations: 

• The real-time preview will likely have artifacts, however you can bounce the clip to itself; this uses the offline, high-quality iZotope Radius stretching algorithm. For reasonable amounts of time-stretching, the quality is quite good.
• You can’t “roll out” a loop like you can with Groove Clips. However, you can copy it and “Paste Special” for as many repetitions as you want, starting wherever you want.
• Clips stretched with DSP don’t follow tempo or pitch changes.

 
“Tape Varispeed” Effects
This does time-stretching like the old tape varispeed options, as described in this article. It uses the Loop Construction view, but has nothing to do with creating loops. Like tape, it is remarkably free of artifacts but does alter formants.
 
Limitations: 

• Stretching time also changes pitch, although sometimes this is what you want.
• This isn’t something the Loop Construction window was designed specifically to do, so sometimes you need to trim the resulting clip.

 
 Anchoring One-Shots to the Timeline
This is more like creating “do it yourself” REX files. For example suppose you drag a kick one-shot to each beat of a measure. If you speed up or slow down the measure, the kicks will still be on each beat. Although this is time-consuming, with proper editing you can have a part that stretches to almost any tempo. Check out this article for more details. [https://www.soundonsound....ch-drum-loops-smoothly]
 
Note that you can use AudioSnap’s “Split Beats into Clips” function to cut a file into one-shots, and anchor those to the timeline. This can speed up the process considerably with clips that have well-defined transients.
 
Limitation:

• It takes time to build loops this way.

 
 But Wait! There’s More!!
 
Although it’s not a SONAR core program solution per se, you can also use Melodyne to stretch time. However I haven’t really delved into it that much, because the DSP stretching function does the job and sounds good.