Design overview

Marble is all about being subtle. Where typical synth filters are too coarse, Marble takes over. It is the perfect tool for warming up modern analog and digital oscillators, a complete patch, or a stereo mix. During performances, a single knob provides intuitive control over tonal changes. Additionally, Marble can serve as a refreshingly different wave shaping tool and modulation effect.

Marble is based around the concept of spectral tilting. A single knob allows you to tilt the frequency spectrum of an input signal around a fixed point: boosting low frequencies while dampening the high or vice versa (see figure). The slope of this tilting curve is special too, it approaches 3db/oct at maximum. This is much more subtle than any ordinary filter can achieve, those give at least 6db/oct, but more often 12 or 24db/oct. Sound dampening at 3db/oct is also a naturally occurring phenomenon, which is why it sounds so natural and organic to us. It emerges for instance when sounds are propagated through humid air, but also emerges in vocal timbres, in our tonal preferences for a good “master mix”, and in the way certain vintage electronics affect the sounds (e.g. as side effect of BBDs: bucket brigade delays). Rob Hordijk has written an inspiring piece about the concept, and provides a digital implementation for a virtual modular synthesizer.

Marble provides you with two independent (and optionally stereo-linked) channels of tilt control, both can be CV controlled. While spectral tilting affects predominantly the highs and the lows, a switch allows you to shape the mid range instead, either by cutting or boosting a wide bell-shape in the middle of the spectrum. Finally, feedback control can increase the depth of the effect, as well as pushing Marble’s output into pleasantly soft saturation.

HINT: The implementation of tonal shaping in Marble is based on all-pass filters. This means that tonal adjustments coincide with small changes in phase. Normally this can not be perceived, as slow adjustments are made by hand. However, when Marble is controlled by fast CVs, these changes in phase can result in a subtle vibrato-like effect on top of the tonal changes. This makes Marble a lovely modulation effect, not unlike aspects of a leslie-speaker or ‘Uni-Vibe’ effect.