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I finally got my hands on a Casio CTK-1000. It is unfortunately excessively bulky (like a 1970th Antonelli; at least the speakers are not bad). The synthesized IXA presets respond nicely to velocity and not only turn brighter and louder, but partly into metallic and resonant distorted timbres (physical modelling?). Picked strings, organs and synth pads are very nice. It can sound like a warm analogue synth and is well suited for new age music. In any preset sound 3 synth parameters {wave, attack, release} can be edited and saved as user preset. Their values can be 1..9, where 0 is the default. The behaviour of 'wave' depends on the preset sound. What sucks is that many brass, string and ensemble timbres are only loop samples with sampled vibrato, which of course changes speed with the note pitch until the next (well audible) split zone is reached; this rather reminds to 1990th Bontempi GM home keyboards or Potex sound toys than a serious synth. Despite many DSP effects, there are no vibrato or tremolo settings; instead many voices contain an annoying delayed vibrato that can not be disabled. Obnoxious is also that there seems to be no easy way to play in the chord section chords without rhythm or accompaniment. (May be you can program this as a "style", but thats not what a keyboard should do.) There is no key split mode except as part of some "split" preset sounds. The entire thing somehow feels like an ill designed cross between MA-130 kiddy keyboard and a very serious workstation. Absolutely insane is that despite complex multi-track sequencer with even editable styles and synth user presets there are no means at all for backup, so the only way not to loose them is to have fresh D-cells inserted and keep the AC adapter connected while changing batteries. (Why is there not even SysEx dump!? An SRAM upgrade module like those for SK-series could fix this.) The manual even warns to disable auto-power-off (hold 'tone' button and switch power on) during programming to avoid data loss. Interesting is that at least through midi (haven't tried) the sound engine is multi-timbrale and there is a "local off" mode that may permit to route the keyboard input through a PC to circumvent some design flaws (e.g. key split). Despite superficial similarities to the Casio VA-10 (both from 1993), the ICs are much bigger and have nothing common. main ICs: CPU= "NEC D939GD 010, 9315BA 006" (160 pin SMD, PCB label "UPD939GD-00X, NM-110", 20 MHz? crystal clocked)key velocity IC= "Casio HG52E35P, CDHG256, 3C33, Japan" (64 pin SDIL)ROM= "NEC D23C16000BCZ 065, 9314E7003, Japan" (42 pin DIL, 2MB)SRAM= "NEC D43256AC-12L, 9310AD019, Japan" (28 pin DIL, 256KB)DRAM= "Sanyo LC33832PL-70, 3DD0, Japan" (28 pin DIL, 256KB pseudo-static, PCB label HM65256BSP)DAC= "NEC D6376CX, 92498H003, Japan" (16 pin DIL)panel CPU= "NEC D78CP14CW, 9246PX701, Japan" (64 pin SDIL, 12 MHz crystal clocked)power amp= "LA 4620, 2J1" (23 pin SIL)IC= "F MB3771, 311F40" (8 pin DIL, PCB label "MB3771P")2x IC= "Mitsubishi 5216A 2607R" (8 pin DIL)transistor array= "LB1216, 3N9" (16 pin DIL)transistor array= "LB1233, 1H8" (16 pin DIL)optoisolator= "NJL 51270,2Y" (6 pin DIL)3x hybrid= "B9HC0118, 101Kx8" (9 pin SIL)The 16 bit ROM (I dumped it) is 2MB large and contains plenty of samples and curves, as well as plenty of strange wavy ramps; possibly IXA employs the mysterious "triangular wave modulation" (https://www.google.com/patents/US5164530). With ROM removed, the panel LEDs and display ("00") look normal, but nothing responds and no sound. The CPU "NEC D939GD 010" (160 pin SMD, 20MHz) seems to be successor of the MT-540 CPU ("NEC D938GD 005", 120 pin SMD, 2.17248MHz), but unlike the latter it interfaces velocity sensitive keys and parts of the control panel through 2 external large ICs and uses most of its 160 pins to access SRAM, DRAM and 2MB ROM simultaneously (no shared bus) to increase throughput per clock cycle. Despite high complexity it fortunately does not run hot and so neither shortens its own lifespan not that of the batteries. Strange is that parts of the control panel are handled by a fairly large CPU "NEC D78CP14CW" (64 pin SDIL) on a daughterboard with ribbon cable wired to empty IC holes on the panel PCB. This hints that Casio had planned a different user interface (perhaps a professional synth?). Many D78CP14CW pins are unused; most do nothing but some output matrix signals. Possibly an LCD was planned but no software written for it. Annoying is that you e.g. can not see the effect settings and so have to tweak sound by ear and count button presses (MT-750 did the same). Also the menu structure is quite restrictive; e.g. various mode changes stop rhythm. Perhaps the panel CPU was added to save computing time in the main CPU, which has more sound glitches and irregularities than MT-540. E.g. effect buttons cause strange transient pop noises, the sample split zones are much more audible (i.e. lack interpolation) and the awesome algorithmic program loops synthesis sounds are gone. (I.e. the 'sound effect' preset consists here only of a bunch of very plain behaving loop samples.) Knowing that MT-540 was a high grade variant of the softsynth-on-a-chip (Casio SA-series), I guess that Casio threw a lot of goodies out of their algorithm to save computing time for the IXA synthesis, effect section and higher polyphony. The only special behaving preset is 'synth-lead 2', which stays always monophonic with portamento, which hints that there are many hidden synthesis parameters. The effect section DSP may be in fact hardware (seen in Casio patents) and likely uses the DRAM. So it might be possible to install a microcontroller between CPU and RAM to edit further parameters or at least backup its content on persistent memory. It also may be that the strange D78CP14CW can be replaced with a programmable microcontroller to unleash hidden synth capabilities of this thing. Somewhat similar like CTK-1000 is the much smaller Casio VA-10 "Voice Arranger", which also has a DSP effect section and can route microphone input through it. But the ICs are different: CPU= "NEC D911GF 003, 9243AA005, Japan" (120 pin SMD)DSP?= "OKI M6583-04, 2432202, Japan" (60 pin SMD)DRAM= "Toshiba TC51832APL-85, 9236HAK, Japan" (28 pin DIL, 32KB pseudo-static)op-amp= "XRAI5218, 245 214A" (8 pin DIL, PCB label "M5218APR")power amp= "Motorola AN8056, 2'D6" (28 pin DIL)3x hybrid= "B9HC0118, 101Kx8, 2N" (9 pin SIL, PCB label "CNB8X101K")hybrid= "B9XC0118, 101Kx7, 20" (8 pin SIL)Although the main voice preset sounds resemble much Casio SA series keyboards, the main ICs strongly differ from all other small Casio keyboards. The double sided PCB is fairly complex with 3 large digital ICs and plenty of discrete components. The CPU "D911GF" is such exotic, that not even Google finds its name. As expected, also the "OKI M6583" has no datasheet, but plenty of Mitsubishi ICs with "M6583..." (different pin count) are audio delay DSP for reverb and echo effects in things like karaoke machines, so technical relations would be very plausible.

Triangular wave modulation (US patent 5164530) is an FM-like Casio speciality that generates waveforms by modulating a monotonous carrier function with a sine (or other) wave and decoding the signal by mirroring it at a triangular wave. With the same count of operators (here only 2?) the produced waveform has higher harmonics than normal FM because at high modulation the wave peaks fold back into the opposite direction. Without modulation it outputs a sine wave and so can nicely blend between very dull and bright timbres. The carrier waveform stands in ROM and so can be switched between a variety of timbres. Like with FM, operators can be combined in various ways. https://www.google.com/patents/US5164530 - Is TM part of the "phase distortion" engine or something else? I own a CZ-230S and revived a CZ-101 (had severe water and fire damage), but I am no PD expert and never heard about TM synthesis before (even websearch doesn't help much). Is this used in phase distortion synths (e.g. the later VZ-series) or is this only used in the Casio "Pulse Code Modulation" engine of preset sound keyboards? Patent 5164530 suggests that Casio at least planned to make dedicated TM synthesizers with a PD/FM-like user interface. I am reworking my technical keyboard descriptions for the WarrantyVoid site. So I websearched for 1980th keyboard patents and discovered a lot of interesting info. https://www.google.com/patents/US5319151 This is what I wrote for my SA-series page: The Casio "PCM" sound generation is apparently described quite detailedly in the US patent 5319151; it is based on a highly complex softsynth with many algorithms those can perform PCM, DPCM, FM and TM (triangular wave modulation) synthesis with sophisticated envelopes. This rather confusing 121 page tome of a patent text however is ambiguous, because it covers plenty of different implementations those e.g. can employ different counts of chip-internal sub-CPU cores for sound generation in higher grade instruments. The SA-series is surely the cheapest described "First" or "Second Embodiment" which has none. The algorithms for this version even describe how shorter tasks are stuffed with blank "dummy commands" to keep the timing in sync when different sounds would need different computing time. It works indeed very VCS2600-like - a marvel of freakish realtime programming made from one big loop (plus in "First Embodiment" one timer IRQ to compute waveforms and fill the DAC output FIFO; the "Second" does even this during dummy commands). The interpolation method with that Casio smoothly blends between wavetable sections is described in the US patent 4442745 "Long duration aperiodic musical waveform generator" It plays sections of compacted samples back and forward to implement things like long decaying cymbals. US patent 4958552 explains algorithms how envelope data is extracted from natural instrument recordings and applied on loop samples as a approximated segmented functions. The original envelope may be removed from the stored loop sample by a waveform normalizer (US patent 4691608). Most important is that these chained envelopes can have basically any length and have (unlike e.g. ADSR) no fixed count of steps. Combined with crossfading between adjacent loop samples this permits very flexible sound definition. The US patent 5319151 "Data processing apparatus outputting waveform data in a certain interval" mentions for the "First Embodiment" that the chip size is only 5x5mm, a program word has 28 bits (including lower potion of next address) and these further hardware specs: "With regard to the circuit scale and the operation time of the specific embodiment (PCM sound source system capable of producing eight polyphonic sounds) the control ROM has a size of 112K bits, RAM 445.4K bits and the control data/waveform ROM (for 100 timbres) 508K bits; one machine cycle is about 276 nanoseconds with a maximum number of cycles of the interrupt program when invoked being about 150; and the executing period of the interrupting process (tone output sampling period) is about 47 microseconds." Expressed in KBytes this would mean 55.7KB RAM, 14KB program ROM and 63.5KB sound ROM, which isn't far away from a Commodore C64 with large ROM cartridge. Said CPU speed would be about 3.6 MIPS. Higher grade MIDI keyboards like MT-240, MT-540 or MT-750 certainly have sub-CPU cores for 16 bit sound generation. Their external ROM is 512KB up to 1MB. Interesting is that OKI made a general midi sound IC ML2860 (32 note polyphonic ADPCM) to play high quality ring tones in mobile phones, but the datasheet from 2002 contains a very strange note: "Please appreciate that ML2860 is not offered for musical instrument and toy applications, such as keyboards." This suggests that OKI licensed an efficient sound synthesis engine (possibly even surplus ICs) from Casio keyboards, but had to sign an agreement not to use it in competitive products against Casio. - Does anybody know more about this sound engine?