UBZR1 ADSR Module

Chelys Lyra

Summary/Usage

UBZR1 contains two ADSRs to allow for two distinct contours with distinct timing and sustain levels.

ADSR1 purpose is fixed to feed the VCAs of the three VCOs and the Noise Generator. ADSR1 hence controls hence the loudness contour.

ADSR2 can be used for various purposes and is available via the modulation matrix. It can for example control the VCF cut-off frequency.

Functional Description

The ADSR module is fully voltage controlled.

My design uses a 1/2 LM 13700 transconductance amplifier as a voltage controlled integrator.

Attack, sustain and release output voltage levels can be chosen freely between −5 V and +5 V. Thus you can generate any contour shape with three different levels, e.g. also an inverse contour.

I am not aware of any similar ADSR designs. Originally I designed this feature to avoid analog multiplication and to move multiplication of ADSR control voltages out to the controlling digital part.

Another unique feature is the multi-output capability: The ADSR can be easily extended having more than one output. Distinct ADSR outputs can have completely independent attack, sustain and release output voltage levels. However, they all share the same timing.

In UBZR1, this feature is used to feed the VCA inputs of the VCO1, VCO2, VCO3 and Noise modules. Mixing of loudness of the sound producing devices is achieved by properly adjusting the ADSR voltage levels.
By manipulating the sustain levels, you can for example mix a VCO with an Attack+Decay envelope with another VCO with runs an Attack+Release envelope.

ADSR1 and ADSR2

For UBZR1, I built two ADSR devices: ADSR1 and ADSR2. They are both triggered by the keyboard gate signal. The two ADSRs have the same core architecture but differ in the outputs provided:

ADSR1 has four control voltage outputs. These four outputs are connected to the VCA inputs of the VCO1 - VCO3 modules and the Noise Generator module
ADSR2 has no volate output. Instead it has aa current output with exponential characteristics. The polarity of the current output can be switched. ADSR2 is used for modulation

The VCOs and/or Noise modules can be viewed as alternating polarity current sources, whose amplitudes are modulated by ADSR1. Note that VCO3 can be operated as LFO

ADSR2 can be viewed as an oscillator which is standing still, i.e. has frequency zero. The polarity, hence the phase, can be switched by a logic input. This feature allows for inverse contours.

These views are useful when considering modulation scenarios, where either ADSR1+VCOx+Noise secondary current outputs are used to modulate and/or ADSR2's current output is used to modulate. The fact that UBZR1 uses current outputs instead of voltages is convenient to easily add the signals of multiple sources.

Performance Specifications

Common ADSR1 and ADSR2 Performance Specifications

Five phase AHDSR operation: Attack, Hold, Decay, Sustain and Release
Voltage controlled Attack, Decay, Release timing: 1 ms to 10 s. Hold timing is fixed at 2 ms

ADSR1 Performance Specifications

Four voltage outputs with independent Attack and Sustain voltage levels between −5 V and +5 V
Release voltage levels are fixed to −5 V, as you will always want to mute the VCAs when the keyboard gate is off. This is an ADSR1 wiring option and not an ADSR1 design limitation.
Maximum sink current of each output: 0.12 mA
Outputs are short circuit protected
Front panel LED for visual feed-back of ADSR performance. The LED tracks the voltage level of output #0

ADSR2 Performance Specifications

One current output with independent Attack, Sustain and Release current levels, with exponential scale between 0.05 µA and 0.5 mA
Current can be switched between positive (source) and negative (sink) operation by a CMOS logic level input.
Additional voltage control "Wheel" input (between −5 V and +5 V) to scale the output current. The default setting is at 0 V.
Front panel LED for visual feed-back of ADSR performance. The LED tracks the logarithm of the current output

Schematics as SVG (Scalable Vector Graphics)

You can directly download the schematics by right clicking.

ADSR1

ADSR1 Block Schematics

ADSR1 LED Meter Schematics

ADSR1 Dual Integrator-A Schematics

ADSR1 Dual Integrator-B Schematics

ADSR1 Control Schematics

ADSR2

ADSR2 works similarely to ADSR1. It has only one current output, however.

ADSR2 Block Schematics

ADSR2 Single Integrator Schematics

ADSR2 Zero Frequency Schematics

ADSR2 Control Schematics

Interface

ADSR1 Inputs

Gate/Trigger (logic level)
Three timing continuous controls (−5 V to +5 V)
Four times two continuous controls (−5 V to +5 V) for Attack and Sustain voltage levels

ADSR1 Outputs

Four envelope voltage outputs (−5 V to +5 V)

ADSR2 Inputs

Gate/Trigger (logic level)
Three timing continuous controls (−5 V to +5 V)
Three continuous controls (−5 V to +5 V) for Attack and Sustain and Release current levels
Logic level input to switch polarity of the current output

ADSR2 Output

Current output (−0.5 mA to +0.5 mA)

Acknowledgements

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