Casio SD Synthesizers

Due to some programming limitations plus Casio's poor marketing, the SD synths never gained wide popularity and are now fairly rare in the second-hand marketplace (which adds to their charm, according to some).

There still exists a small but devoted fanbase who insist that SD synthesis, particularly as expanded in the high-end model HT-6000, was overlooked and highly underrated and today rare.

The 1987 Casio HZ-600 was the initial model and was considered an entry-level offshoot of the "Z" series of synthesizers that included the CZ and VZ lines.

The subsequent SD synthesizers were marketed as advanced home keyboards (i.e., including speakers and programmable accompaniment) launched under the HT prefix (with the notable exception of the non-editable, preset-only Casiotone versions, the MT-600 and CT-630).

The SD sound source is a 4-bit (16-step) digitally controlled oscillator (DCO) that uses waveforms including triangles, sawtooth, squares of different widths, and some unusual pulses, plus various combinations thereof.

The user has very limited influence over the spectrum dynamic using the DCA envelope, and doing so is something of a trial-and-error process.

In effect, each so-called "waveform" of an SD synth consists of 2 layered sub voices with independent preset volume envelopes (that cannot be changed by the user).

[citation needed] Thus, some "waveforms" crossfade between timbres without filter sweep to simulate e.g. the brighter attack phase of metallic clangs or picked strings.

The top-of-the-line Casio HT-6000 offered 64 possible waveforms, 4 DCOs per voice, velocity, detuning, ring-modulation, and an expanded SD parameter set.

In contrast to the bulky-looking Casio CZ line, the HZ-600 was deliberately styled after the sleek-looking Roland Alpha Juno 2 right down to the inclusion of an "alpha-dial" programming wheel.

The HZ-600 included 3 levels of onboard analog chorus, 3 selectable keyboard split points, 3 selectable pitch-bender ranges, a modulation wheel, transpose, and a card slot for the new sleek Casio RA-100 RAM cards, which had 8K of memory.

While not technically a synthesizer (the tones could not be altered and new sounds could not be created), it used the SD synthesis engine and had the same preset patches as the HZ-600 (arranged in a different order).

It included the "Ending" and "Auto Harmonize" features but did not have any pitch bending capability, even through MIDI.

Like the HZ-600 (but in distinction from the MT-600 and HT-700), it had 61 full-size keys, a modulation wheel, a volume-pedal jack, MIDI THRU, and a 3-point splittable keyboard.

Like the HZ-600 but unlike the others, the HT-6000 had a complete parameter list silkscreened on the outer panel, somewhat alleviating the need for a manual.