Casio Cosmo Synthesizer SPU (1984), ZZ-1 (1986)

The Casio Cosmo Synthesizer was a prototype computer-based workstation instrument conceived along the lines of the NED Synclavier and Fairlight CMI. It was most notably used by Isao Tomita on Dawn Chorus, where he used the waveform drawing feature to sonify astronomical radio signals. The complete system consisted of a computer (Casio FP-6000S with monitor, keyboard, mouse, graphics tablet and an expansion unit containing special interface cards to connect to the other hardware), controller keyboard (Casiotone 6000, which is velocity and pressure sensitive), MIDI interface, 2 SPU units (sample playback) and 6 PDU units (phase distortion; these are apparently roughly equivalent to the CZ-101 or CZ-1000, but with no control panel). Everything was controlled via MIDI, but the SPU units also connected directly to the computer for waveform editing. The PDU modules likely use the same µPD933 ICs as the CZ series, but possibly with 16 bit linear DACs rather than the CZ’s lower quality floating point DACs. The CZ-101 and CZ-1000 were introduced a few months after the Cosmo Synthesizer, but the SPU remained in development for two more years as the ZZ-1. It was apparently completed and ready for production, but was canceled because it seemed to not be commercially viable. Only very vague specifications were released, and of course no service manuals are available, but both the SPU and ZZ-1 are described in greater detail in several patents.

The MIDI interface, SPU, PDU and ZZ-1 are shown in this video:

The original brochure is available here.

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SPU front panel

SPU tone generator block diagram

The SPU is described in US patents 4681008, 4970935 and 5160798 (these are nearly identical), with a more detailed description of the hardware given in patent 4667556. It’s a 4 note polyphonic sampler with VCAs for amplitude scaling and no filters. It performs 12 bit linear sampling at 40 kHz and has 128 Ki x 12 of sample memory for about 3.28 seconds of sample time. This can be divided into up to 8 samples of arbitrary length, which are assigned to different keyboard zones and velocity levels, each with its own set of voice parameters. ADSR amplitude envelopes are generated in software. The SPU has 4 output jacks for each of the 4 voices, plus a mono mix output. At heart, the SPU appears to be a very basic sampler, although it’s velocity sensitive and introduces some advanced features, like triggered sampling with pre-recording, velocity switching of multisamples and automatic selection of loop points at zero crossings. Its biggest asset is that the waveform memory can be read and written by the host computer via a dedicated bus. This enables software-based waveform editing, synthesis and drawing using a mouse or graphics tablet. Another very unique feature is that each of the voice channels can independently be used to either read from or write to the waveform memory. This means that it’s simultaneously capable of sampling and polyphonic sample playback. In the SPU, this is only used to monitor the sound as it’s being sampled. In the ZZ-1, however, this feature is further exploited to obtain modulation delay and resampling effects. Other details are less clear, but it appears to use time mutiplexed phase accumulators with linear interpolation (17 integer bits and 13 fractional bits). This makes the SPU the first sampler to use linear interpolation (although there were synthesizers that did this going back to the Allen Digital Computer Organ in 1971). It’s also vaguely implied that the playback sample rate might be 160 kHz (since the phase increment when recording samples is 0.25).

Linear interpolation

Japanese patent JPH06110466 describes the SPU’s editor software that ran on the FP-6000S computer. There was also software for editing the PDU’s sounds, a 16 track real time sequencer and a separate step sequencer that displayed notes on a staff. There are some screenshots of the sequencer software here.

Sound loading screen

Editing the waveform using the mouse

Setting sample start, end and loop points

Sound parameter edit screen

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ZZ-1 front panel

ZZ-1 tone generator block diagram

The ZZ-1 was intended to be the commercial version of the SPU. Yukihiro Takahashi (ex-Yellow Magic Orchestra) and Hajime Tachibana (ex-Plastics) served as design consultants. Takahashi may have recorded the drum sounds for the RZ-1 (which were later reused as lower quality samples in the MSM6294 ICs), and I think Tachibana, who also worked as a graphic designer, designed the front panels for the ZZ-1 and some of the CZ models (so you can think of him as you struggle to clean the dust out of the crevices of your CZ-5000). The ZZ-1 is mostly similar to the SPU, retaining the computer interface. This seemed to be modified for use with computers other than the FP-6000S, although I don’t know what platforms Casio intended to support. The sample memory is still 128 Ki x 12, but the samples can now be recorded at 5, 10, 20 or 40 kHz. It also adds polyphonic voltage controlled filters and the ability to use its simultaneous sampling and playback capability as either a 3 tap modulation delay (described in patents 4864625 and 5050216, which are nearly identical) or for 3 note polyphonic resampling, sample mixing and overdubbing (described in patents 4754680, 5025700 and 5136912, which are nearly identical). The channel used to write to the waveform memory can also pass the input signal directly to the DAC, so that the dry signal can be present in the output without requiring an additional analog signal path. The ZZ-1 has two types of feedback, one from a single delay tap (between the VCF and VCA) and a second that feeds the mix out (the sum of all delay taps) back to the input. It’s described as offering delay, reverb and chorus effects, but I expect the reverb would be very poor, really just a multitap delay with one tap used for feedback. The delay effects should be approximately comparable to the Korg SDD-3300. It should also hypothetically be possible to implement pitch shifting, though this isn’t mentioned in the patents. It must be noted that the ZZ-1 can function either as a sampler or a delay, but not both at the same time. The ZZ-1 also has 8 outputs on the rear panel. While this might seem to imply 8 note polyphony (i.e. adding a second tone generator that shares the same sample memory), I think it’s more likely that it’s still 4 note polyphonic, and the 8 outputs are for the 8 different samples (this would be useful as a drum sampler). This would mean that the ZZ-1 also adds some signal routing circuits.

Modulation delay example for a chorus effect

It seems that by the time the ZZ-1 was ready for production in 1986, it wasn’t really a competitive product. Compared to the competition, it was overpriced and underpowered. Even with the unique and fairly powerful delay functionality and resampling/overdubbing capabilities, a sampler with only 4 note polyphony and 128 KiWords of sample memory was unimpressive. Likely these restrictions were fixed into the designs of custom ICs and thus could not be easily improved. At the same time, the exchange rate was rapidly becoming less favorable for Japanese companies. The estimated price of the ZZ-1 was ¥ 1,000,000. In early 1985 this would have been about 4000 USD; by mid 1986 it was about $6400. For comparison, the Sequential Circuits Prophet 2000 came out in 1985 and cost about $2500, and the Emu Emax was introduced in 1986 starting at $2995. Both of these were considerably more capable samplers than the ZZ-1. The ZZ-1 seemed to get an unenthusiastic reception from prospective distributors, so its release was canceled. The FZ-1 was quickly developed as a more professional sampler, apparently by some of the same team that designed the SPU and ZZ-1. It was released in 1987 for ¥ 298,000.

Other than the SPU, the ZZ-1 doesn’t seem to be related to any other Casio product. It’s likely that it was based on one or more custom ICs that were never produced in quantity. It did, however, influence Casio’s later designs. The FZ and SK models do have a few things in common with the ZZ-1, and the linear interpolation and high playback sample rate were used in many subsequent Casio products. It’s also possible that the VCFs used in the ZZ-1 may have been the NJM2090 ICs used in the HT and HZ models.