Time stretching (and time expanding !) is an useful feature for those who produces remixes, mashup / bootleg, or want special FX.
Time stretching consists in changing the speed of a sound without changing its pitch.
The inverse operation is called pitch shifting : changing the pitch without modifying the speed.

Wavosaur has no native timestretch feature but Wavosaur has two pitch modifiers :

– Simple pitch shift
– High precision FFT pitch shift

The simple pitch shift modify the speed when you change the pitch : it acts like a goold old turntable if you set your 33 rpm LP record to 45 rpm => pitch increase ! welcome to the chipmunks.

13 Best Sampler VST/AU Plugins; Both Free and Paid! Last Updated on December 15, 2020 by Facundo Samples can be used to create some pretty cool sounding music and the way most producers use them can vary a lot. On this site you’ll find a completely free library of guides to VST instruments, royalty free sample packs + learning music production/beatmaking. Whether you’re a complete beginner to music production, or an intermediate/advanced level producer looking to sharpen your toolbox, we are here to help.

The High precision FFT pitch shift is a special effect for changing the pitch without changing the speed.

These two features are in the “Process menu”
and now the magic :

Let’s try with a vocal sample, open it in Wavosaur :

https://blog.wavosaur.com/wp-content/uploads/2013/08/01.-Marvin-Gaye-I-Heard-It-Through-The-Grapevine.mp3 this is the normal vocal sample without any treatments https://ameblo.jp/conspasswichan1985/entry-12632828600.html. Best free vst i synthesizers instruments for edm for ableton.

now go to menu -> Process -> Pitch Shift -> High precision FFT, and let’s change the pitch to an extreme setting : X 2 (one octave higher)

https://blog.wavosaur.com/wp-content/uploads/2013/08/02.-Marvin-Gaye-I-Heard-It-Through-The-Grapevine-pitched.mp3 this is the pitched chipmunkized version of the vocal sample!

and now, go back to the original pitch : menu -> Process -> Pitch Shift -> Simple : and now set the pitch one octave lower ( – 12 semitones) : this will also change the speed (two times slower)

https://blog.wavosaur.com/wp-content/uploads/2013/08/03.-Marvin-Gaye-I-Heard-It-Through-The-Grapevine-stretched.mp3 this is the time expanded version

Free Time Stretching Vst Plugin

with these two operations you obtain a time stretch / expand : pitch is the same, but speed as changed ! This is more effective for voices, solo tracks… but don’t hesitate to experiments.

Just don’t forget your calculator, if you need to make something less trivial than one octave up / down.

The FFT pitch shift can be long to compute, you can also use free pitch shift VST plugins instead of the native Wavosaur effect.
Here’s some freeware plugins for pitch shifting (without changing speed):

Spectral Monkeyage

download here : http://www.ochremusic.com/specMonkyageSt.zip

4Band Shifter

4 Band Shifter

download : http://bitterspring.net/pitchshifter/

Free Timestretch Vst

Audio time-stretching is one of the most complex audio processing tasks, and as such, is incredibly hard to create from scratch. It’s not something one developer can quickly code, which is why they will search the internet for free, open source audio time-stretching and pitch-shifting solutions first.

The two most promising and often cited findings are Rubber Band and SoundTouch. Let's take a look at their pros and cons, and then compare Superpowered’s Time Stretching and Pitch-Shifting to those.

Rubber Band Library

This is a big library with lots and lots of code inside. The audio quality is great, as the author did a solid job researching audio algorithms. It handles audio transients well (not losing them) and does a great job in preserving audio quality (reducing so-called “phasiness”).

But the digital signal processing work is not stellar, Rubber Band’s CPU load is so high that you cannot run it on a mobile device for real-time processing, even if you try to utilize every DSP hack and trick you might know.

You can learn more here.

SoundTouch Audio Processing

A nice, compact library with an acceptable CPU load, it can work real-time on a mobile device. But SoundTouch’s time-stretching works in the time domain.

Free Time Stretch Vst

There are basically two kinds of time-stretching methods: time-domain and frequency domain. The aforementioned Rubber Band (and all quality commercial audio libraries) work in the frequency domain for highest audio quality.

Vst plugin lpfilter. Time-domain stretching works with overlapping windows, providing absolutely no “phasiness” with the cost of missing or doubling some parts of the audio, which sounds strange. And, even if you handle transients somehow, the overall result sounds too “compressed”.

SoundTouch does not handle transients, so it doesn’t work for most modern music, unfortunately. A prominent unwanted audio artifact is oddness with drum kicks. It either misses them completely or doubles them.

You can learn more here.

The Reality of Free, Open-Source Audio Time-Stretching and Pitch-Shifting

“Free” time-stretching and pitch-shifting solutions cannot be used for commercial mobile projects, typicall because of audio quality or CPU problems (or both!). Solving either of those is so complex that only commercial solutions should be relied on -- that said, many commercial solutions still don’t run well on mobile devices!

Allow us to suggest: Superpowered Real-Time Time Stretching and Pitch-Shifting

It has outstanding audio quality (you can test it) and has the highest performance on mobile devices.

Last thing, check out C++ Audio Library List (2018) here.

• Audio Codecs
• Audio Library
• Audio Transient
• Pitch Shift
• Soundtouch