Model 24 Heisenberg Generator

Random Source

The Model 24 Heisenberg Generator is the first computer-based module in the Plan B line. Taking it's name from Werner Heisenberg (the father of the Uncertainty Principle), the Model 24's primary function is a dual wide-band random voltage generator producing simultaneous and fully independent stepped and smooth arbitrary voltages. Along with these random events, it can also be used as a Sample and Hold, a VC Lag Processor, a VC Trigger Generator, a Gate to Trigger Converter or a Digital Noise Source. The Model 24 also provides VC inputs for all of its tactile controls. While totally self contained - producing its own pacing triggers and random states - its also open ended, and will accept external triggers and voltages independently.

A true analog/digital hybrid (Click here for a block diagram), the M24's on-board 10mHz Atmel 2051 microcontroller serves three primary functions:

1) Digital Noise. Two independent algorithms replicate the functionality of the long-extinct National MM5837 Digital Noise chip..with 16 bit resolutionThere are no D to A converters in the Model 24. There will be no zippering (stepping). An analog source is derived by filtering a flurry of 2 x 64,000 possible random gate signals generated by the 2051. All secondary processing (Mean, Deviation, Chaos, Meter) is executed in an analog domain.

2) Clocking. The second function assigned to the microprocessor involves two pseudo-random trigger streams, both quantized internally to 8 (smooth) and 5 (stepped) degrees of musical time:

Figure 1 - Internal trigger streams of the Model 24
These quantized triggers are adjustable in real time. The internal generators operate by counting cycles received by an on-board analog LFO which paces their execution.

If the trigger algorithms we've presented are unappealling or do not fit your needs at any given time, patching an external clock sequence of your own design is an easy option.

3) Non-linear Dynamic Slewing. In most cases, analog synthesizers replicate smooth (interpolated, i.e.'wiggley') random events by filtering an internal stepped source through a dynamic lag processor. The slew time of these filters vary in proportion to the velocity of the root voltage shifts. There is an inherent problem with this approach, however, in that the slewing tends to smooth out the finer details when slow patterns are dialed. By incorporating the processor to generate the triggers which pace the parent voltage source, the Model 24 compensates for this anomaly. A dedicated output sends a flag on all trigger durations of less than a quarter note in duration. This signal is then used to choke the slew time as these shorter events occur. The net effect dramically increases the resolution at slower settings. The Model 24 reacts to short events regardless of the speed and slew time, it doesn't overlook them.

4) Gate to Ttrigger Conversion. The Model 24 Stepped Function Generator will output any pulse or trigger it receives (either internally generated or from an external clock) and convert it to a 3ms long trigger pulse which is taken to the faceplate via the Trigger Out jack>

Operation:

Although functionally complex, the Model 24 is remarkably musical and user-friendly. Bi-color (green/red) level indicators give precise indication of the output level of both the smooth and stepped functions.

The two primary manual controls (MEAN and DEVIATION) adhere to standard deviation indices used in the statistical analysis of uncertainty.

Figure 3 - MEAN and DEVIATION controls
The Mean pot sets the relative midpoint, the vertical displacement of the output voltage's center point (see figure 4).

Figure 4 -Effects of MEAN adjustment on a single waveform
The Deviation pot controls the variance (both positive and negative) from the mean, the spread from the midpoint (figure 5) .

Figure 5 - Effects of DEVIATION control settings on a single waveform. MEAN remains constant
The voltage patterns shown in figures 4 and 5 are identical, yet illustrate the effects of various settings of the MEAN and DEVIATION controls.

I/Os:

Outputs: All of the Model 24's critical signals are brought to the user interface. Along with the stepped voltage output, it's internal trigger is also available (TRIG OUT) so that external devices such as envelopes and other triggerable control generators can be easily synced with the M24's pseudo-random musical intervals. The smooth generator also makes it's internal noise generator available (SOURCE OUT).

Inputs: The Stepped generator has a dedicated input for an external drive (EXT TRIG). Another interesting feature can be easily patched by setting the DEVIATION pot fully CCW while controlling the MEAN function by an external signal. The otherwise steady state behaves as a Sample + Hold (stepped gen.) or a Slew Limiter (smooth gen.) Set up in this fashion, output voltages of the stepped and smooth generators track the VC MEAN signal, with the pot acting as a manual offset to the incoming voltage. The Stepped Generator holds these voltages until the next trigger is recevied, the Smooth Generator applies a portemento, the slew time (ranging from .5 seconds to OVER FOUR MINUTES!!!) determined by the CHAOS pot setting.

Theoretical Notes:

The design of a stepped random voltage function is a relatively easy analog computation. A smooth random function however, as defined in the M24 as a sloping, continious random event is much more involved. Three key elements (the range of the internal VC LFO driving the quantized random pulse generator, the algorithm incorporated to generate those quantized random triggers, and the slew rate of the VC lag processor) continually interact to create the final outcome and must track one another in tight unison to maintain a unified personality over the entire range of a single pot (Chaos) and to keep from stalling. In the case of the Heisenberg, many considerations had to be met to achieve this goal, as the elements involved cross betwen the analog and digital domains twice before their final analog processing (sample and hold and slew limiiting). We feel the Model 24 meets and exceeds those expectations.