Comparison of Audio Time Stretching Algorithms

TL;DR Jump to the Hard test and listen to the Original and to the Length 200% column.

The Contenders

Amazing slow downer by ronimusic. Slow Down Type IV was used, unless mentioned otherwise.
Elastique Efficient by zplane. Default settings.¹
Elastique PRO by zplane. Default settings.¹
Quantum by Tachyon Sonics. Default settings.
Radius from RX 10 by iZotope. "Best quality" with default advanced settings unless mentioned otherwise.
Rubberband by Breakfast Quay. Settings: Mid/Side, Pitch Mode: HighQ, Window: Long, others left to defaults.^{1, 2}
SoundTouch by surina.net. "High quality" preset was used.^{1, 2}
SuperPV from TS2 by IrcamLab. FFT Size was set to 4096 (default setting 2048 seems more adapted to solo tracks). Other settings left to defaults.
Tachyon by Tachyon Sonics. Crisp/smooth was set to -0.25. Other settings left to defaults.
ZTX from Time Factory II by Zynaptiq. Settings set to: ZTX, Smooth (l=4), Best, High localization.

¹ Tested using Reaper
² This is an open source algorithm.

The Light Test

Notes:

Throughout this page, playing any audio excerpt will automatically stop the previous one if not finished (unless JavaScript is disabled)
All audio excerpts are loudness-normalized using EBU R128 to facilitate comparisons (foobar2000's replay gain feature was used)
Audio excerpts are encoded in mp3 using LAME 3.100 (Setting: v2). I have found the mp3 artifacts negligible compared to the audio time stretching artifacts; but you may disagree

Original
Algorithm	Length 110% (slower)	Length 160% (slower)	Length 50% (2 times faster)
Amazing
Elastique Efficient
Elastique PRO
Quantum
Radius
Rubberband
SoundTouch
SuperPV
Tachyon
ZTX

The Hard Test

Original
Algorithm	Length 130% (slower)	Length 200% (slower)	Length 320% (slower)
Amazing
Amazing		(1)	(1)
Elastique Efficient
Elastique PRO
Quantum
Radius		(2)	(2)
Rubberband (3)
SoundTouch
SuperPV
Tachyon
ZTX
ZTX	(4)	(4)

Notes:

(1) With Slow Down Type II instead of IV
(2) Transient sensitivity set to 0.4 instead of 1.0, noise generation to 1.0 instead of 0.2
(3) Transients set to "Mixed" instead of "Crisp"
(4) Without the "High Localization" option

The Speed Test

This table shows the time it takes to transform 60 seconds of stereo, 44.1 kHz audio at 110% of the length. The tests were performed on the same reference computer.

Algorithm	Time in seconds (smaller means faster)
Amazing	2.6
Elastique Efficient	0.69
Elastique PRO	1.0
Quantum	4.2
Radius	12.0
Rubberband	2.51
SoundTouch	0.92 (high quality) / < 0.25 (fast - sounds similar)
SuperPV	2.8
Tachyon	144.0 (quality 4) / 48.0 (quality 3 - sounds almost the same)
ZTX	16.8 (best) / 2.5 (good - sounds almost the same)

Musical References

[Light Test] John Lennon, "Imagine", Imagine (2010 - Remaster), EMI Records LTD, 2010

[Hard Test] Sia, "Bird Set Free", This Is Acting, RCA Records, 2016