FIG. 3: These sonograms resulted from analyzing typical synthesizer sounds with an exponential scale in which each row is a harmonic of the fundamental. The sounds are: sawtooth and square waves (top), sawtooth with decay and attack envelopes (middle), and sawtooth with volume and filter LFO (bottom).

A little of this, a little less of that. The Image Synth is easily configured for additive synthesis, and with the use of both graphic and audio filters, it produces a unique collection of synthlike samples and multisamples. Fig. 3 shows Image Synth analyses of six typical analog synthesizer sounds: unfiltered sawtooth and square waves (top row), sawtooth with decay and attack filter envelopes (middle row), and sawtooth with LFO applied to volume and filter cutoff (bottom row).

These analyses were made with a custom Frequency Map in which each row’s frequency is a harmonic of the bottom row’s frequency. Rendering these with sine waves gives a reasonably accurate additive replica of the original sound. However, because the phase relationships between the harmonics can vary with each rendering, the resulting sound does not have the same graphic waveform. A sawtooth rendered additively, for example, does not look like a sawtooth in the Sample Editor.

Add ’em up. For pure additive synthesis, an exponential Frequency Map should be used. Other custom scales can be used for additive synthesis, but typically they should contain at least as many steps per octave as the picture height, and the steps should bear some harmonic relationship to each other (more on this in a moment).

Building an additive sound in the Image Synth gives you control over each individual sine component’s amplitude and pan envelopes. For each component, start with an empty window and use the Line brush to create a line at the desired harmonic (that is, row). Then use filters or the Filter brush to color and contour the intensity of the line. Finally, save the line as a preset, clear the Image Synth, and work on the next harmonic. Saving the individual components as presets lets you mix and match them later to create any number of sounds. You can do this by recalling the first preset, copying it to the clipboard (type the C key), recalling the next preset, adding the clipboard data to it (type E), copying the composite result to the clipboard, recalling the next preset, and so on.

A faster approach is to work on several rows at a time. You could do this by creating a horizontal blue grid and using it as a filter to select groups of rows. To quickly create the grid, activate the blue channel, set the Hot Filter Grid Size to the desired row spacing, type G to create a blue grid with this spacing, and use the Rotate tool to rotate the grid to horizontal. If there is unevenness in the grid, drag the Contrast and Luminance tool to the right to eliminate the contrast. Next select the red and green channels, type I to invert the empty Image Synth to full yellow, and select “Filter with Blue” channel. As before, use filters and the Filter brush to contour the remaining lines, then save the image as a preset. After you’ve filtered the full-yellow image with the blue channel, use the Arrow keys to move the remaining lines up and down as desired to create the other harmonics.

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Reprinted with permission from Magazine, February, 2001
© 2001, Intertec Publishing, A Primedia Company All Rights Reserved