Details on the Pittsburgh Modular Fragments Generator

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Full details via Pittsburgh Modular

"The 'Fragments' are a set of pings, or short bursts of sound created by a trio of Twin-T filters. The Twin-T filter circuit was used by some classic analog drum machines to create percussion sounds. Realistic tom-toms, congas, and kick drums can all be made using this method. The Twin-T filters included in the Fragments Generator have been adapted and optimized for a specific purpose. The idea was to create an analogue method of generating sounds at the level of individual "grains" or "fragments" similar to a traditional digital Granular synthesizer. By approaching the process from another angle we have come up with an entirely new sub-genre of synthesis.

The sound produced by the basic Twin-T filter is quite close to the idealized grain, a decaying sine-like waveform that can easily be varied in amplitude, frequency, and position. Typically, the Twin-T filter produces a single sound up to a few times a second. What would happen if that occured a thousand or more times per second? The Fragments Generator creates a constant tone that consists of overlapping and interacting fragments which can be manipulated in a number of ways.

Amplitude
The amplitude of each fragment is set at its initiation. This is important as just creating a variable mix of "full strength" tones would not relize a wide enough scope of fragment-to-fragment variability.

Position
The relative position of each fragment is variable in order to manipulate the overlap between them.

Frequency
The frequency (or timbre) of each fragment is variabe over time so that (in theory) each fragment is unique.

Being analog and having to obey the laws of comman sense (and physics) the Fragments Generator is limited to 3 distinct fragments. This number is perfect because it allows for plenty of complex interaction, and even better, the sounds produced by the Fragments Generator do not sound like the digital sampling type of granular synthesis. Although they can each be described using a similar set of terms, both forms of synthesis produce a unique sonic footprint.


Controls (starting from the bottom left)

FREQ Knob - Controls the frequency of the internal VCO. The internal VCO can either be used to determine the main pitch generated or as a source of "jitter" between fragments, or both.

FM Knob and Jack - Attenuator for the FM input. EXP and FM are control voltage (CV) inputs for the VCO.

AMP Knob and Jack - Offset control and is added to the control voltage (CV) introduced by the AMP input jack.

Timbre Konb - This controls the centre Frequency/Q of all 3 fragments.

TCV Knob and Jack - Attenuverter for the TCV input jack. Used to add or subtract a voltage from the Timbre knob.

ALT - A 2nd Timbre control voltage (CV) input that affects the 3 fragments differantally, a positive control voltage increases the frequency of fragment 2 and decreases that of fragment 3.

SPREAD Knob - This controls the relative postions of fragment 2 and 3. With the pot all the way counter-clockwise all 3 fragments occur at the same time, as it turns clockwise fragments 2 and 3 are moved away from fragment 1. All 3 fragments can occur within a cycle (set by FREQ) so imagine an ideal ramp drawn on graph paper as a cycle, with three points drawn on it. #1 is always at the start of the ramp, #2 and #3 might also be at the start but turning SPREAD will move them along towards the end of the cycle. If they go too far they won't occur, so, SPREAD is also a way of controlling the number of fragments.

SCV Knob and Jack - Attenuverter for the SCV input jack. Used to add or subtract a voltage from the Spread knob. The SCV jack is normaled to the internal oscillator.

IN - this is an input that will replace the internal VCO in "driving" the fragments. The built in VCO is a stripped down version of the VCO found in the Pittsburgh Modular Generator its main job here is to make the module self contained. Users that need better tracking and/or stability are encouraged to substitute the VCO of their choice. The signal introduced at the IN socket does not have to be a VCO. Any non DC signal such as a pulse train from a trigger sequencer or something like the Timetable can be used for making voltage controlled percussion.

Internal VCO - As well as providing a handy way of making sound straight out of the box by driving the Fragments Generator the Internal VCO is also internally routed to the SCV input (via a normalled / switching jack) this provides a usefull source of 'jitter' to help animate the fragments without any external modules.

TRI - Output of the Triangle wave from the internal VCO.

Fragment Output Jacks (1, 2, 3, MIX) - There are outputs for each Fragment (1, 2, 3) and a mix output to maximize potential for internal feedback or spatilization. Because Fragments 1 and 2 can effectivly be "switched off" with the Spread controls, outputs 2 and 3 could be routed to the left and right of a stereo mix, with output 1 or MIX in the middle giving the user control over the "location" of the sound as well as its pitch/amplitude/timbre.

As usual users are encouraged to experiment with internal feedback and having the TRI out patched into the ALT or TCV inputs is also another interesting source of sounds. When using an external VCO, output 1, 2 or 3 could be used to FM the Internal VCO setting up all kinds of complex interactions."