RTGS3 Icon

Tutorial 4: Transposition Tricks

Perhaps the most unique feature of RTGS3 is that grains can be transposed either microtonally or according to a user-specified pitch grid. This tutorial is divided into 2 sections:

Microtonal Transposition

RTGS3 lets you transpose grains to a high degree of microtonality, which lets you build up dense clouds of grains with a rich spectral signature. For the first part of this tutorial, let's recreate a classic granular synthesis technique using a sine wave as our source sound.

Step 1

First, fill the Buffers with a sine wave at 440 Hz. If you don't remember how to do this, refer back to Tutorial 0 part 1, steps 3-5.

Often in these tutorials we've been filling both Buffers with the same audio material. This is because when RTGS3 generates grains it alternates between reading audio from each buffer in turn (ie, it does not read audio from both Buffers for each grain, but uses only one Buffer at a time). There is of course nothing stopping you from filling each Buffer with something different - in fact this can lead to interesting results and is part of what makes RTGS3 unique.

Step 2

Now let's set up a Generator Controller to generate line segments at a moderate speed in a single direction. (If you don't remember how to do this, refer back to Tutorial 2 part 3, steps 1-2.) The default setting of the Generator window does just what we need:

GeneratorRampsWindow
Step 3

Set the Grains Density slider to use the Generator 1 Controller by CMD-clicking it and selecting "Generator 1" from the menu that pops up. You'll see that the slider starts to move to the right, however for the purpose of this tutorial we actually want the slider to go the other way. Click the Grains gear icon twice so that the "Limit Slider Controller Input" pane is exposed. Now click the Invert button so that it is hilighted:
GrainsDensityControllerInvert

Go back to the sliders by clicking the Grains gear icon twice and you'll notice that the slider is now moving in the opposite direction.

Step 4

Set the Transposition Amount Random Range to use the Generator 1 Controller by CTRL-CMD-clicking the Transposition Amount slider and selecting "Generator 1" from the menu that pops up. Set the Mode to "Microtonal" and the Range to "8 octaves":
TranspositionsettoGenerator1

Step 5

Turn the Grains On to hear the result. This is an example of how linking a single controller to different parameter sliders can lead to interesting output.

Experiment with the Grain Envelope 2D slider, for instance by setting it all the way to the bottom-left corner, to get an idea of the range of textures you can get. You could also try setting the 2D slider to use the same Generator Controller as the Grains Density and Transposition Amount sliders.

Back to top


Pitched Transposition

Let's again borrow one of Apple's guitar samples to demonstrate the power of RTGS3's pitched transposition feature.

Step 1

Open the Buffers window by clicking the "View Buffers..." button in the Buffers section of the main interface window. Load the file /Library/Audio/Apple Loops/Apple/Apple Loops for GarageBand/Acoustic Picking 06.aif into both Buffers.

If you don't have the GarageBand Loops installed on your machine, see if you can find an acoustic guitar sample in your own collection or on the internet to use for this section of the tutorial.

Step 2

Make the following settings in the main window:

Grain Density = 10 milliseconds

Grain Length = 200 milliseconds

Transposition Mode: Pitched | Set to: Pentatonic | Range: 2 octaves

Transposition Amount = set the Random Range from 0. to 12. semitones

Panning Mode: Alternate L/R | Panning Random Range to Full (-90 to 90 degrees)

Step 3

In the Buffer section, turn Loop On and click the Play button on the Buffer Automation controls so that the Buffer Position slider starts to move to the right:
BufferAutomationControls

Turn Grains On to hear the result.

Step 4

For an even more impressive effect, slow down the Buffer Position slider by setting the Speed menu in the Buffer automation controls to "1:8". You might also want to EQ out the low frequencies and boost the highs somewhat to give the sound an airy quality:
EQHighBoost

We'll look at more of RTGS3's Effects capabilities in Tutorial 6. For now, see if you can make the EQ setting shown above on your own.

We've had a glimpse of something really special in this tutorial: time stretching. It's one of the most interesting ways of applying granular synthesis techniques to sampled sounds, and has the potential for creating very rich output that can go on for hours. In the next tutorial we'll take a closer look at this technique.

Back to top