Ian Fritz Panel #1 - The Timbre Tantrum

Ian Fritz modules in 4U


DoubleDeka Ultrasonic VCO

This unique VCO consists of an ultrasonic oscillator core followed by a parallel pair of waveform generators. Each waveform generator consists of a switched multi-octave divider followed by circuitry to generate a 10-step waveform using a set of 10 slider potentiometers. Also included are a novel synchronization circuit with two different operating modes and a built-in "digital ring modulator" (DRM) for producing a wide variety of synchronized and anharmonic sounds. The oscillator core is highly stable (better than 20 ppm/K in the prototype) and features wide-range, accurate tracking (better than 0.05% over fifteen octaves). The variable waveform generator provides fine control over an enormous range of available timbers.

Teezer Through-Zero FM VCO

This module is a sawtooth-based VCO capable of frequency modulation (FM) extending past zero frequency into the negative-frequency regime. Thru-zero FM provides a much wider and richer variety of sounds than "ordinary" (positive frequency only) FM.

The negative-frequency version of a waveform is simply a time-reversed replica of the original waveform. When a VCO is modulated through zero frequency, the waveform slows down to a stop and then speeds back up in the reverse direction. Here is a picture of the core sawtooth wave being modulated to negative frequencies. On the left side of the picture the wave is a down ramp, and on the right side it's an up ramp, with the zero frequency point being at the broad dip.

The Teezer's output waveforms also include triangle and sine waves, for producing sounds with fewer high harmonics, as typically used for bell sounds, train whistles, and so on. The unit also features a variable synchronization control that can be adjusted over a range of settings from hard sync to a fairly loose soft sync.

The module can also serve as a highly accurate and stable "ordinary" VCO (i.e., without the deep FM), with upramp, downramp, triangle and sine output waveforms.

Wavolver II Waveshaper

The Wavolver is a novel, versatile waveshaper that generates a special kind of double-pulse waveform along with an extra folded-wave section added between the pulses. It generates a wide range of timbres from a gentle sine or triangle wave to a very rich signal with multiple zero-crossings per cycle.

The module can be driven by any continuously varying signal. For simplicity let's assume a Tri wave at the input. The circuitry works by only passing the input signal when its amplitude (positive or negative) is above a threshold set by the Pulse Width control. When it's below the threshold the output signal is zero. This is shown on the left side of the following figure. The signal consists of steeple-shaped pulses that can be swept from narrow for high harmonic content to full width, which results in a triangle wave ("Width" and "Width mod" controls). This represents a wider range of timbres than from the familiar rectangular pulse generators, which give a square waves at full width.

In addition to the double-pulse generator, the Wavolver has circuitry to generate a series of evolving folded waves between the pulses. These are mixed into the output via the "Fold mix" control. The right side of the above figure illustrates the folding at a 50% level for two different pulse widths. The folder output is available separately to allow individual processing of the double pulses and the folds.

The double-pulse signal consists of a positive pulse and a negative one, and the resulting signal has odd harmonics only. The capability to produce waves with strong, odd-only harmonics is practically never seen in classical VCO/waveshaper designs. There is a wide area of timber space available here that has been largely ignored. Adding the folder output produces high-energy even harmonics in the signal's spectrum.

In the Wavolver II there are several ways to modify the basic waveforms discussed above. First, the amplitude of the second pulse can be continuously tuned from -5V (as shown above) to +5V ("Pulse 2 amp" control). At full positive amplitude, the signal has two identical positive pulses, resulting in a signal at twice the frequency of the driving signal. Waves with the second harmonic stronger than the fundamental are musically useful, as some acoustic instruments (bowed strings) share this characteristic.

Another way to change the basic waveforms is to add a DC voltage offset to the input signal ("Offset" and "Offset mod" controls). A positive offset makes the first pulse stronger and wider and at the same time it make the second pulse weaker and narrower. Again, this adds even harmonics into the output spectrum and results in some interesting timbres, especially when modulated. The graphic below illustrates these modifications.

Finally, the waveshape can be modulated by modulating the input waveform.

Threeler VCF

This filter design is different from the usual filters found in analog synths. It consists of three first-order filter sections that can be switched between either high-pass or low-pass response. A four-position mode switch allows selection among four different combinations of these responses. A voltage-controlled resonance amplifier allows operation of the filter well beyond the onset of oscillations. In this regime the circuit's nonlinearities provide a wide variety of phase-locking and chaotic outputs. Signals are available from all three filter sections to provide the widest variety of waveforms and filter responses.

Below is a highly schematic diagram of the operation of the different modes of the device. The three rectangles indicate the three filter stages, each with a lowpass and a highpass input. The triangle represents the clipped variable gain stage that provides the resonance feedback.

With a low resonance setting, mode 1 is a third order lowpass filter, with outputs available from the first, second, and third order circuit points. Similarly, mode 4 is a third order highpass filter. Modes 1 and 2 are types of bandpass filters with different slopes above and below the center frequency.

With a high setting of the resonance control the filter will self-oscillate in all four modes, with a variety of waveshapes depending on the filter mode and output stage used, as well as on the resonance setting. Using high resonance along with an input signal results in many interesting waveforms due to phase locking and other nonlinear effects. These are most easily produced by using a relatively low input gain. With four modes and three outputs there is plenty of interesting nonlinear territory to explore.

5Pulser Waveshaper

This circuit is a voltage-controlled waveshaper that produces a train of output pulses that may be varied in number, width and position in response to a control voltage. When fed with a sawtooth waveform, the pulses evolve from a single square wave to a train of five pulses occupying half a period or less of the output waveform. The switches S1-S4 allow different combinations of pulses to be used.

2Q/4Q Multiplier & 4-Input Mixer

An analog multiplier that can be switched between two-quadrant and four-quadrant operation. As an analog synthesizer module it can thus function as a voltage-controlled amplifier (VCA) or as a ring modulator (RM). The circuit board for this project carries two copies of the 2Q/4Q circuit plus an independent four-input mixer with standard and inverted outputs.

Operation is the same as other VCA and RM modules. As a standard VCA, audio goes into the X input and control voltage goes into the Y input. The Bias control can give the VCA an "initial"gain, useful for AM applications, such as tremolo, etc. As a RM, the "carrier" goes into the Y input, and may be mixed into the output with the Bias control. At full bias, the output is just the carrier signal with no modulation.

All the above copied from Appliancide: http://appliancide.blogspot.com/2014/06/now-available-from-uglysound.html


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No info about availability.

submitted Feb 17th 2014, 20:10 by DomMorley | last Change Jun 6th 2016, 09:24 by isvisible

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