sScale is an instrument for realtime visual and aural exploration of harmonically resonant noise. The program is controlled with the mouse and keyboard to change various parameters of the sound processing algorithm, such as pitch, and attributes of the rendered graphics, such as color and blur amount. The underlying source of data is three independent channels of pink noise running through a highly resonant comb filter.
sScale Flow Diagram
Pink noise is generated by summing 12 octaves of white (uniform) noise. The octaves of white noise are produced by generating and holding a unform random value every 2^{n} samples, where n=0 is the highest octave. A feedback comb filter is simply a signal summed with a time delayed output of the filter.
Feedback Comb Filter
The feedback in the system causes linearly spaced resonant nodes, harmonics, in the frequency spectrum. Harmonics of some frequency, f, are defined with the equation h_{n} = nf where n is the set of all positive integers. Using positive feedback with a comb filter produces even harmonics and using negative feedback generates odd harmonics. By controlling the delay time of the comb filters, the pitch of the resultant sound can be modified.
The audio samples are represented visually in two different ways. The first of these is a timedomain phase plot which maps the leftchannel samples to the xaxis, the rightchannel samples to the yaxis, and the third, unheard, channel to the zaxis. In this mode, Lissajous figures resembling clouds of particles and complex tangled strings are produced. Curiously, by making the filter create odd harmonics, the figures display a high degree of spatial symmetry. Using positive feedback, i.e. even harmonics, makes curves that are completely asymmetric.
Symmetric Form (odd harmonics)

Asymmetric Form (even harmonics)

The second mode of visualization is a polar plot of the leftchannel data in the frequency domain. An FFT is performed on the timedomain data and the magnitude and phase of the sinusoids is plotted. This mode creates a ringlike cloud of rapidly orbiting particles. By muting the noise going into the comb filter, the particles spiral inward forming something like a galaxy.
Frequency Domain Ring

Muting Filter Input



Screenshots
TD = timedomain FD = frequencydomain
TD [Random Walk]
TD [Harmonograph]
FD [Dual Vortex]
FD [Seashell]
TD [Atom]
TD [String Field]
FD [Wormhole]
