FIG. 4: MetaSynth-style additive synthesis is accomplished by creating lines for each desired harmonic. In this figure, the harmonics have been panned (red/green aspect) independently, and some tremolo (intensity variation) has been added at the end. The blue lines serve as a grid but don’t affect the sound.

Fig. 4 shows an example with blue gridlines spaced eight rows apart, harmonics added on two rows within each section, and the fundamental in full yellow at the bottom. An increasing tremolo was added to the right half of the image. You can render this image, then use the resulting sample in the Sample Editor as a sound source. (See the sidebar “MIDI Sequencing with MetaSynth and Xx” to see how you can use standard note sequences to trigger sounds.) However, the standard disadvantages apply: the sample’s length and tremolo speed will change when transposed, and the upper harmonics will become unnaturally shrill at higher pitches. Building a multisample will produce better results for use in either a MetaSynth Instrument or another sampler.

To build a multisample, simply render the image using different tunings. Spacing by major or minor thirds usually keeps the speed changes of any motion (for example, tremolo) within acceptable limits. Additional lowpass image filtering for each octave change in pitch knocks down the shrillness. Finally, appending the tuning pitch to the end of each sound file’s name will facilitate building instruments from the multisamples in MetaSynth and many other samplers. In MetaSynth, selecting “Build Instrument” from the Instruments menu—then selecting any of the sound files—results in all of the samples being loaded, set to the correct root pitch, and correctly mapped relative to the semitone Frequency Map.

FIG. 5: Displacement is one of the many graphic tools MetaSynth provides for manipulating an additive-synthesis image. From top to bottom, the frames show the displacement map; the original additive image; the result of displacement; fade-in and fade-out filtering; and phasing and lowpass filtering.

Beyond the norm. You can produce interesting and unusual samples by using custom scales and some of MetaSynth’s more graphic tools. One of the most interesting ways to create a custom scale that works well for additive synthesis is to analyze the harmonic spectrum of some sampled sound. This technique works with any sound, but pitched sounds work best. Once you have loaded a sound file, select a region in the sustained part of the sound and choose Instant Spectrum from the Morph menu. MetaSynth extracts the harmonic spectrum of a small clip at the selection’s beginning. To import the spectrum file as a custom scale, first select Custom Scale from the Frequency Map menu. In the Custom Scale window, hold the Option key and click the Open icon (the disk with the upward-pointing triangle). Use these custom scales to build additive samples as you would with the Exponential scale.

The Displacement tool stands out as one of the more creative tools for image manipulation. This tool moves pixels in the Image Synth based on the intensity of pixels in the displacement-map picture. Fig. 5 (middle frame) shows the result of applying the displacement map shown in the top frame to the picture shown below it. Displacement can be applied with or without automatic smoothing; smoothing is usually desirable in this context.

The Filter Palette is another place to turn for sculpting unusual sounds. One thing to remember is that graphic filters can be applied to any selected part of a picture. The bottom two frames in the figure illustrate this—first, semicircular filters were applied to the right and left quarters, then a phasing filter was applied to the bottom horizontal section, and finally, a lowpass filter was applied to the middle horizontal section. The resulting picture produces various speechlike effects when rendered with harmonic-spectrum Frequency Maps. You can also use the Hot Filters or groove filters, like the bass groove described previously, to add rhythm and motion to the sound.

When applying filters, keep in mind that any MetaSynth filter can be applied in two ways: graphically to a picture before rendering or as a 128-band EQ to the sound file in the Sample Editor. Applying a filter graphically is generally harsher because its effect is absolute—filtered-out pixels make no contribution to the sound. Audio filtering, on the other hand, produces resonant peaks and valleys.

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