UBZR1 Modulation

Chelys Lyra

Modulation "Wheel"

UBZR1 Modulation Wheel Processing

To control the musical performance, UBZR1 is using an analog wheel at the analog keyboard (well it is actually a "slider" type potentiometer, because that I had available). The keyboard interface is combining this "Wheel" analog voltage with another voltage coming from the "Digital-In" module. It generates the larger of the two. The combined signal, called "Wheel*", can be used to control the amount of modulation in real-time (provided modulation is enabled).

This combination of keyboard and Digital-In levels allows to force a "minimum" modulation via the Digital Interface and potentially increase it via the keyboard.

Modulation Overview

UBZR1 Modulation Matrix Overview

Modulation in UBZR1 is implemented using a concept of a "modulation matrix": a set of modulation sources can be "patched" to a set of modulation destinations.

A full matrix would imply all n:m combinations are available. However, there are some considerations, that limit the number of useful combinations:

One source usually modulates one destination only. Exception: vibrato using VCO3, to modulate the pitch of both VCO1 and VCO2
More than one source could modulate the same destination simultaneously, although not likely more than two
If there is overlap between sources and destinations, then some combinations do not make sense. E.g. if VCO3 is source, it does not make sense to modulate VCO3 pitch.

The implementation specifics:

Mapping from source to destination does not need to be the same for all sources
If all mod. sources are current sources, then summing two or more sources is simple, to modulate one destination. The destination just has to provide a suitable input summing resistor.

Modulation Sources

UBZR1 Modulation Sources

UBZR1 has the following modulation sources:

VCO3 current output O₁. As VCO3 can be used as a low frequency oscillator (LFO), this source is important for vibrato type modulation
VCO2 current output O₁. VCO2 can be used for occasional special modulation situations, because VCO2 usually runs at audio frequencies
ADSR2. ADSR2 timings and contour can be set independently from ADSR1. UBZR1's implementation is specific because ADSR2's voltage contour output is not used directly to modulate. Rather, ADSR2 steers an exponential current source. This allows both for very smooth and also very strong modulation.
In fact, the exp. current source can be thought of an oscillator with zero frequency. A polarity switching logic signal determines the "phase". This allows to deliver also an inverted contour.
Above diagram shows the symmetry of the exp. current source behind ADSR2 and the VCOs and the Noise sources, whose VCA output currents are also driven by exponential current sources
Noise current output O_P/R, which offers the pink or red "wave forms". This is useful for random type modulation.

The overall amount of modulation can be controlled by the Wheel* signal, which can be controlled both by the keyboard and by the Digital-In module.

Note that VCO1's O₁ current output is not available as modulation source, because it is used for the ring-modulator functionality (together with VCO2).

Modulation Destinations

The following diagram shows the four audio generating modules (VCO1-3 + Noise), the voltage controlled filter and their modulation capabilities:

UBZR1 Modulation Destinations

UBZR1 has the following modulation destinations:

VCO1 exponential (i.e. Volt/Octave) frequency modulation
VCO1 and VCO2 linear frequency modulation. This does not change the average pitch and is well suited for vibrato
VCO1 rectangle pulse width modulation
VCO2 exponential frequency modulation
VCO2 rectangle pulse width modulation
VCO3 exponential frequency modulation
Filter exponential frequency modulation

Modulation Matrix Detail

UBZR1 Modulation Matrix Detail

The chosen implementation of the matrix is a compromise. There are multiplexer switches per source and a fixed "wired" matrix, with choices of "useful" combinations. The four multiplexers can not be switched independently, but are rather coupled in pairs:

Pair A: the sources VCO3 and VCO2 go together, and
Pair B: the sources ADSR2 and Noise go together.

Note that for pair A, there are two unused states.

The four multiplexers are controlled by 3-bit logic signals, three bits per pair.

Modulation Matrix Concept

The following table shows another representation of the chosen matrix. Entries:

"-" marks combinations which do not make sense, because a source would modulate itself
"sym." are combinations that would be redundant because of symmetry, i.e. you could swap VCOs 1 and 2, because they provide the same functionality
"?" denotes combinations that might be useful
Arabic numbers indicate the state of a multiplexer switch pair. For example A1 stands for state 1 of pair A, B1 stands for state 1 of pair B. The choice of numbers is arbitrary. State "0" does not appear in the table because it stands for the modulation "off" state = no modulation from these two sources
"n.a." are combinations that might be useful, but are not available because there are no more multiplexer switch states available.

Destination Source	VCO1 PW	VCO2 PW	VCO1+2 Lin.Freq.	VCO1 Exp.Freq.	VCO2 Exp.Freq.	VCO3 Exp.Freq.	Filter Freq.
VCO3 O₁	sym.	A1	A2	sym.	A3, A5	-	A4
VCO2 O₁	?	-	-	?	-	A5	?
ADSR2	B1	sym.	not useful	B2	B3	B4	B5
Noise O_P/R	sym.	B6	B7	n.a.	n.a.	n.a.	n.a.

Please note, that VCO3 can run both as low frequency oscillator (LFO) and at audio frequencies. Thus, VCO3 could be used for vibrato effects, when run in LFO mode.

VCO2 can only run at audio frequencies. When used as modulation source in combination with VCO3 (state A5) , there can be chaotic sound effects because of non-linear feed back.