Tutorial 3: Creating Slammin' Filter Sweeps with Displacement Maps

In this tutorial, we create a filter that mimics an analog synthesizer's filter sweeps using the new Displacement Map feature. Displacement Maps are pictures which can be used to warp an image in the Image Synth or Filter windows. When an image is displaced, its pixels are shifted up or down, right or left depending on the shading of the displacement map. Where a displacement map is neutral gray no displacement occurs. White and black displace pixels in opposite directions.

Step 1. Build the Filter

A) Choose a starting filter

For our example we want a narrow band filter. We can start with a filter that is a simple horizontal stripe such as this one: 

Tip : such a filter can be created easily on the fly. Press the delete key to delete the current filter. Use the marquee tool to make a selection the same width as the filter you want to create.  Press 'i' to invert the selection. Choose blur more from the processes submenu.

B) Choosing a Displacement Map
In the filter Palette double-click on the Displacement tool 

Click on the pop-up menu's icon  to show the available displacement maps and choose this picture

Make sure that "Smooth before displace" has a check mark since we want smooth curves in our filter.
Press  to confirm the choice and exit the dialog.

C) Reshape the original filter.
Click on the Displacement tool and drag the mouse up and down to bend the contours of the filter. In this example, we are mostly interested in vertical displacement. We constrain displacement vertically by pressing the option and shift keys while dragging.
The picture will look something like:

Your filter is now ready to be used .

Step 2. Use the Filter

A) Choose the first preset from the file "Tut3_presets" and compute the sound. A saw wave was used to give the result a lot of harmonics.
B) In the Filter window, press the Analyze Current Sample icon . This step is optional, but it is generally useful as it shows  how the filter overlaps the source sound.
Use transpose tools  or  to adjust the overlap between the filter and the source sound.

C) Press the Compute Sound icon  to Apply the filter to the sound


Conclusion
Using Displacement Maps, you can easily create complex filters from simple elements. Of course, you can save any filter you create for later use.

IDEAS FOR FURTHER EXPLORATION:

The filter in the example above may attenuate the bass frequencies a bit too much. Using steps similar to those described above, you could construct the filter shown below which removes less of the the low frequency content.

Create sweeps in time with the underlying music by using the picture from which a sound was computed as the displacement map. For example,  in the Image Synth choose preset #1. Apply the Maximum Hot Filter. Copy the picture. In the Filter window, double-click the displacement tool and paste the picture. Now, use the displacement tool on the narrow band filter. Try this with smoothing on and off.