Overview
TG55/SY55 Synth Architecture
TG55/SY55 synth architecture
Oscillator
TG55 inherits SY77/SY99's PCM synthesis engine with less PCM ROM.
While SY77/SY99 can combine FM synthesis engine with PCM, TG55 has no FM.
It is a 16-polyphonic 16-bit PCM synth.
1, 2 or 4 oscillators can be stacked in a Voice.
74 waveforms are contained in 2MB ROM.
Sample rate is max. 48kHz.
There are waveforms of acoustic instruments, 7 electric pianos, 16 drums, 9 synth waves and 11 SE (transients and loops).
Most waves are short-looped and the loop noise is audible in piano sample.
Pitch shift ranges 10 octave, and various aliasing noise can be created.
Filter
Each oscillator can be processed by its own two independent digital filters.
HPF and LPF can be combined to make 4-pole LPF with self-oscillation, or BPF with various band width.
Resonance works only when HPF is not selected.
When Resonance is on, the sound tends to be weaker.
Each filter has its own multi-step envelope.
Unfortunately, when the filter is driven by an envelope, it can't be modulated by LFO or other controllers.
When it's modulated by LFO, the envelope has no effect.
Sometimes the stepwise change of the cutoff can be heard as the parameter resolution is limited.
LFO, Modulation and Effects
Each oscillator can have its own Pitch Envelope and LFO.
Modulation control is rather weak.
There's only one control source - When Modulation Wheel controls vibrato, no other sources can affect vibrato.
There's one DSP Effect - Reverb, not-long Delay, Tone Control, Distortion - but no modulation effect like Chorus.
As there's no non-linear function (Oscillator-to-oscillator modulation, etc.),
TG55's synthesizing ability is limited - it's difficult to move far beyond the image of the internal ROM waves.
To make a new sound with TG55, the multi-mode filter is the key.
LFOs, pitch change and Envelopes would be the additional tools.
Next 
TG55/SY55
Deep Synthesis: Home
3. 15. 2003