Parallel Digital Imaging (PDI)

In 1991, Rodgers introduced a breakthrough in digital sound: Parallel Digital Imaging.  PDI is the first digital waveform processing system to apply advanced digital signal processing techniques to the detailed re-creation of pipe organ voices.  Its custom gate-array, integrated circuit wave processors are each capable of performing over 15 million arithmetic calculations per second.  These are controlled by a network of microprocessors running a multi-tasking operation system developed by Rodgers specifically for musical instrument applications.  PDI is a software-controlled system, with each detail of operation determined by instructions stored in program memory.  This is a powerful and elegant architecture that is markedly more flexible than earlier hardware-driven systems.

All sounds are reproduced in stereo, through multiple 21-bit digital-to-analog converters (DACs).  This ensures accurate reproduction of even the quietest sounds.  As in modern theatre sound reinforcements, the multi-channel audio system is bi-amplified and uses separate subwoofers to avoid excessive intermodulation between low and high frequencies.

To create the PDI Voice Library, actual sounds from carefully selected organ pipes are digitally recorded and stored with the same 16-bit resolution used in audio Compact Discs.  Many of these digital samples were taken from pipe instruments built by Rodgers, while others represent the very best work of many well-known builders.  These samples contain every facet and detail of each voice.  Any number of wave samples of any duration may be used, so that character changes across the compass of the keyboard are always faithfully reproduced.  Sample rate can be optimized for each application - the PDI system supports sample rates up to 60 kHz.  Waveforms are stored in high-density Read-Only-Memories (ROMs), with a typical two-manual instrument containing over 70 seconds of unique samples.

Unlike rudimentary digital sampling systems, the capabilities of PDI extend far beyond simply playing back the recorded samples.  Finite Impulse Response (FIR) interpolators ensure the most accurate reproduction of the recorded waveforms.  Time-Variant Filters (TVFs) enable characteristics such as attack, brightness, and decay to be determined for each note of every voice.  This ability to perform very complex waveform processing, combined with the inherent versatility of direct software control, ensures that Rodgers' PDI system will remain at the forefront of musical technology for years to come.