Overall: 7628 5596 7057 365
30-Day: 7950; 7-Day: 18802; Yesterday: 10882
GSi Compact DeLuxe replicates the italian transistor organ Farfisa Compact DeLuxe, also known as the single manual version of the most famous Compact Duo. The electronic circuit of this kind of organ is relatively simple, at least on paper: rather than using a mechanical tone generator like the tonewheel models (Hammond and Pari), the transistor organs used a circuit called "Top Octave Synthesizer", TOS for short, responsible of the generation of 12 waveforms, one for each note of the last octave of the organ keyboard. The basic waveform was usually something halfway between a ramp and a triangular. The lower octaves were produced by means of "divider" circuits that could halve the frequency of each waveform, going so forth for each lower octave down to the pedalboard tones. At each division, something was lost and something was gained in terms of harmonic content. The result was that the same notes of different octaves had oscillators perfectly in sync, so all C notes were in sync, all C#, all D and so on. This same technique was also used in so-called "string machines" or "stringer keyboards" that emulated orchestral sounds (violins, trumpets, etc.) - see GSi's Electrorchestra.
The various registers in combo organs were produced by passing the raw waveforms through a filter bank, so some waveforms were low-pass filtered for bass-like sounds, some were high-pass filtered for violin-like sounds, etc. and some waveforms also went through more than one filter. This also adds some level of phase shifting between waveforms coming from different registers, the reason why the sum between, e.g. a Flute 8' and a Violin 8' isn't exactly the superimposition of the two waveforms, but something slightly different. And this is one of those underrated details that made the sound of some Combo Organs pretty unique.
The sound engine of GSi Compact DeLuxe is also included in the GSi Gemini as well as in the Crumar Mojo 61.