Basic Architecture
GP Synthesis Chip
Overview
SC-55 as a synth is a simple PCM playbacker with Oscillator - Filter - Amp architecture.
Filter seems to be 2-pole low-pass, and there are chorus and reverb effects.
Up to two sounds can be layered in an 'Instrument.'
Sample ROM is said to be 3MB (SC-55) or 4MB (SC-55mkII).
It's not very clear how much data compression is used and how much actual (uncompressed) ROM is inside.
Access to the synthesizing parameters inside is significantly limited.
Users can only modify some parameters of the preset Instruments.
Tweakable parameters are part of Filter/Amp envelope, Pitch, LFO, Effects and Matrix Modulation, etc.
Envelopes can't be controlled independently.
Waveform selection, LFO routings etc. can't be edited.
GP Synthesis Chip
Roland made a synthesis chip called GP, and used it first in SC-55 and then JV-80 synthesizer line.
Before the arrival of GP, Roland used LP chip for their PCM playbackers (U Series - see U-110 and U-220 pages),
and later powered it up, adding a digital filter and an effects chip in D-70 / MV-30.
GP chip can be thought of as a one-chip-integration of LP/Filter/Effects.
As a member of GP family, SC-55 shares many features with JV;
Layer-able OSC-Filter-Amp Architecture
Can handle compressed PCM data
Each component of OSC, FIlter and Amp has its own independent, multi-step envelope
2 LFOs can be routed to OSC, Filter, Amp
Matrix control for pitch, Filter, Amp, and each LFO's rate and depth -
This last feature even surpasses JV, though we don't know what is exactly controlled in SC.
JV's features below are omitted in SC-55;
Full editability
FXM (Fixed Frequency Cross Modulation - very fast vibrato)
Filter 'Hard' Mode
LFO sync to MIDI tempo, etc.
Roland made it explicit that they used data-compression in JV's PCM ROM.
Its actual ROM size is 4MB, allegedly 8MB contents compressed within.
Many samples in JV and SC share the same origin and the similar character.
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SC-55mkII
Deep Synthesis: Home
1. 7. 2003