There is one simple and easy step to make gold out of crap in music: stretching or slowing down. When you stretch a song five or more times with the right technique you create a relaxing soundscape and therefore made gold out of crap. The following two headlines go a bit deeper in the material granular synthesis. If you just want to get cracking jump to the headline paul stretch.
In our everyday life we get used to perceive in a fixed dimension. Visually, we can change dimension slighty to a certain extend. To zoom out we step back and to zoom in we come close. To take it to the extreme we have to use technology like microscopes or space shuttles. In any way, changing dimension opens up a new world. You see things you didn’t see before or feel differently when observing something.
With video technology we obtained the ability to change the time dimension for films. Everyone who watched some YouTube videos like this knows how different and weird everything looks in slow motion. It is the same for audio. Slowing down audio five, ten or even up to a hundred times really changes it in an extreme way.
In video we shoot 240 pictures per second, slow it down ten times and still have 24 frames per second left to see a fluent video. In audio though, if you simply play it faster or slower the pitch changes proportionally. To keep the pitch the same we have to use a different approach called granular synthesis.
Granular synthesis is method that slices an audio file into small samples called grains to rearrange them in the following way. To slow down audio, grains are layered on top of each other slowly jumping from one grain to the next.
For example: Assume that the window size of a grain is 5 ms, you want to layer 100 grains and stretch the audio 10 times. In that case you have to repeat grain 1 at least 10 times before you go to 2. In order to prevent a stuttering effect of repeating grains you vary the beginning of each layered grain so that they overlap slightly and create a fluent repetition (see illustration). After 50 ms you begin with grain 2.
There is allot more to granular synthesis than this principle but I want to mention just a few important things here:
- To avoid clicks at the beginning and end of each grain a window with fade-in and fade-out is used. Different types of windows use different types of fades and have therefore different names like hanning window or triangular window.
- To get a richer sound the length and playback speed (and therefore pitch) of each grain (and layer-grain) is varied slightly.
- Sometimes, also octaves above or below the original pitch are added to create a full sounding soundscape.
Paul Stretch or Paul’s Extreme Sound Stretch is a small program that utilizes granular synthesis to stretch or shorten audio. You can download it for Mac or Windows here:
A short video tutorial on how to use Paul’s Extreme Sound Stretch:
Rebecca Blacks Friday slowed 5 times:
Quick advice: In my opinion it sounds much better to stretch music that doesn’t have present drums or percussion sounds. Listen to Bach’s Prelude No 1 for Cello stretched or visit my YouTube channel stretchedmusic to convince yourself.
Visit my Stretched Music channel on YouTube
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