Intellijel Cylonix Shapeshifter v1.03 - Manual (Page 25)

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Technical Details
The digital portion of the SHAPESHIFTER module is implemented in an Altera Cyclone IV Field Programmable
Gate Array (FPGA). The use of Gate Array technology rather than a general purpose programmable microcon-
troller or DSP chip allows highly efficient implementation of fast parallel operations.
The primary logic blocks are clocked at a rate of 25MHz. The phase accumulators of the 9 oscillators are up-
dated at this rate, as well as the nonlinear combination operations. This results in very low aliasing noise for
the nonlinear operations and for the frequency and phase modulations. The phase accumulators are 55-bits in
width, allowing for very low frequency operation and high quality frequency and phase modulation.
The contents of the relatively slow wavetable EPROM are copied to fast SDRAM memory when the module is
first powered up. The SDRAM is then clocked at a rate of 100MHz. This results in a fast read rate of the wavet-
ables - when CHORD mode is off the wavetables for each oscilllator are read at a sampling rate of 3MHz. When
chord mode is on the wavetable read rates drop to 700KHz per oscillator, which is still high enough to minimize
aliasing noise. Linear interpolation is performed between successive samples, providing smooth waveforms
even at low frequencies. Each wavetable sample is digitally represented with 16 bits, and each waveform in the
wavetable consists of 512 samples. There are 1024 different waveforms stored in the wavetable.
Most of the signal processing in the module is done at a 25MHz sampling rate. The signals are then filtered and
down-sampled to 98KHz (25Mhz/256) before being output by the Digital to Analog Converters. Some of the
signal processing (the delay line and the vocoder filter banks) is done at the lower output sampling rate. The
PULSE output is sent at the primary 25MHz sample rate, although it is passed through an analog buffer which
rolls off the high frequencies.
The input signals MOD A and FM1 are converted to digital form by 24-bit Analog-to-Digital Converters running
at a sampling rate of 98KHz. The input signals PITCH1, PITCH2, INT. FM, RATIO, SHAPE1, SHAPE2 and MOD B
are converted to digital form with 12-bit Analog-to-DIgital Converters running at 25KHz sampling rates. The
SYNC input signal is sampled at 25MHz and converted directly to a 1-bit digital representation. The FOLD and