CT-6000 - what synthesis/ sound generation does it use?

[Chas]

Casiotone CT6000 model from 1984 - what synthesis/ sound generation does it use? What are the related models?

 

Some of those that know about the workings of the early Casios might know? @CYBERYOGI =CO=Windler can you shed some light on this model?

 

I have a Casiotone CT6000  in my collection, Casio's flagship model from 1984, and it's a very unusual beast for its time as it had a ton of high level features. For instance, it has MIDI, a velocity AND after touch keyboard, Unison modes, lush choruses, a complex  accompaniment section including "Super Accompaniment" that adds fills depending on how the person is playing, a pitch bend wheel with glissando control, and the ability to split and layer the keyboard. These were all rather advanced for a 1984 home keyboard and were not evident in any of Casio's other commercial keyboards up to 1984.

 

Up to 1984, Casio had used mostly Consonant Vowel synthesis for the majority of their keyboards, with a brief foray into Sine Wave synthesis. The CZ's Phase Distortion line was being developed and was due for release in late 1984 in the form of the CZ101 , and many thought that the CT6000 used an early form of preset PD sounds (not to be confused with the CT6500, that DID use preset CZ sounds). However, the CT6000's patches don't SOUND like Phase Distortion to me, and the drums in particular sounds VERY analogue. Additionally, some of it's behaviour doesn't indicate PD synthesis, for instance, when using the pitch bend wheel to go down a whole octave on the lowest note while also holding down a note an octave higher. it isn't capable of doing so without being slightly out of tune. The CZ's had no problem with going down a whole octave and staying in tune. The later Spectrum Dynamics range (HT/ HZ models) appear to share some similarities with the CT6000, especially when dropping that lowest note with the pitch bend wheel and holding down another note an octave above (though the SD HT/ HZ pitch bend doesn't have a full octave down/ up range).

What could the sound generation synthesis be that Casio used for the CT6000? My suspicion is that it is an advanced form of Consonant Vowel, that Casio probably felt had been taken as far is it could go with the CT6000 (possibly used in the very rare Symphonytron 8000 model too). They then concentrated on the CZ Phase Distortion line, along with the SK/ FZ sampling range. Perhaps to offer a lower cost home style preset keyboard (compared with their pro level CZ/ FZ/ VZ range), maybe that is why they developed the HT/ HZ Spectrum Dynamics series by utilising the CT6000's sound engine with some extra editing capabilities and adding an analogue filter(s)?

 

Here's a good video showcasing all its sounds and features:

 

 

Plus some adverts from back in the day:

 

 

[Jokeyman123]

I remember these-this was one I really wanted back then, but couldn't afford it (!)  I had to wait a few years-but then the CZ-101 was included with an electronics course I studied-as part of my training to be a keyboard tech-alas i remained a poor musician instead! I do not know what synthesis engine this used sorry, but the controls look very similar to the SK-2100 which I did get and held onto for quite awhile. Hmm....let's take another look at these.....this was definitely a very nicely designed Casioi.

[Harpon]

Great sounding synth!

[CYBERYOGI =CO=Windler]

I own a Casio CT-6000 and service manual, but haven't analyzed its complex hardware further (beside making PCB photos and contact cleaning). It employs 3 main voice sound ICs "NEC D932G" (64 pin zigzag) and the unique blip percussion IC "Hitachi HD61701" (54 pin SMD), everything controlled by the CPU "NEC 7811G-081".

Although this keyboard was the flagship of 1984, it has nothing to do with phase distortion. The D932G appears to be a velocity sensitive successor of the famous "NEC D931G" (42 pin DIL, found in MT-65 and such). Beside CT-6000 it was only used in the early Casio e-piano CPS-101 (and possibly other CPS-series). It communicates with the CPU through 8 input and 4 output pins, has 17 bit audio and additional 14 control output pins for external filters, mixing ratio, stereo chorus and the like. The velocity sensitive highend midi keyboard contains 3 of these unique sound ICs; each is wired to an own DAC with different fixed analogue filter (each 3 control lines). The outputs are mixed; in chord mode the 3rd sound IC is used for chord only, else all 3 are layered as main voice. I suspect that in classic Consonant-Vowel manner the mixing ratio between multiple differently filtered sound ICs changes with keyboard velocity. The existence of so many switchable filters seems to disprove the rumour that CT-6000 was a secret unofficial first phase distortion instrument. The high timbre quality rather results of 17 bit DAC resolution and complex analogue post-processing through filters and a costly 3 line BBD stereo chorus.

(Interesting is that US patent 4387619 poorly describes a consonant-vowel hardware that implements a so-called "staggered multi-performance mode", i.e. a preset sound can consist of multiple layered subvoices occupying 2 or 4 polyphony channels ("duet", "quartet" - a feature that was not released until the much later "unison" modes in the CPU controlled Casio CT-6000), which needs independent management of key presses and polyphony channels. In the described self-contained LSI chip without CPU control the routing was quite a mess.)

The HD61701 produces 24 lofi percussion sounds through 4 audio outs those are routed through external discrete filters to shape timbres.

[IanB]

Just to add, the only CT keyboard with the CZ Phase Distortion engine is the CT-6500.

[Chas]

On 4/6/2020 at 2:33 AM, CYBERYOGI =CO=Windler said:

I own a Casio CT-6000 and service manual, but haven't analyzed its complex hardware further (beside making PCB photos and contact cleaning). It employs 3 main voice sound ICs "NEC D932G" (64 pin zigzag) and the unique blip percussion IC "Hitachi HD61701" (54 pin SMD), everything controlled by the CPU "NEC 7811G-081".

Although this keyboard was the flagship of 1984, it has nothing to do with phase distortion. The D932G appears to be a velocity sensitive successor of the famous "NEC D931G" (42 pin DIL, found in MT-65 and such). Beside CT-6000 it was only used in the early Casio e-piano CPS-101 (and possibly other CPS-series). It communicates with the CPU through 8 input and 4 output pins, has 17 bit audio and additional 14 control output pins for external filters, mixing ratio, stereo chorus and the like. The velocity sensitive highend midi keyboard contains 3 of these unique sound ICs; each is wired to an own DAC with different fixed analogue filter (each 3 control lines). The outputs are mixed; in chord mode the 3rd sound IC is used for chord only, else all 3 are layered as main voice. I suspect that in classic Consonant-Vowel manner the mixing ratio between multiple differently filtered sound ICs changes with keyboard velocity. The existence of so many switchable filters seems to disprove the rumour that CT-6000 was a secret unofficial first phase distortion instrument. The high timbre quality rather results of 17 bit DAC resolution and complex analogue post-processing through filters and a costly 3 line BBD stereo chorus.

(Interesting is that US patent 4387619 poorly describes a consonant-vowel hardware that implements a so-called "staggered multi-performance mode", i.e. a preset sound can consist of multiple layered subvoices occupying 2 or 4 polyphony channels ("duet", "quartet" - a feature that was not released until the much later "unison" modes in the CPU controlled Casio CT-6000), which needs independent management of key presses and polyphony channels. In the described self-contained LSI chip without CPU control the routing was quite a mess.)

The HD61701 produces 24 lofi percussion sounds through 4 audio outs those are routed through external discrete filters to shape timbres.

 

@CYBERYOGI =CO=Windler - Just realised that I never thanked you properly for this. THANK YOU!  This information is a great help in understanding the workings and sound generation of the CT6000, and as I suspected, it most likely uses an advanced form of Consonant Vowel synthesis. I'm also curious as to whether this sound engine was used in Casios beyond 1984? Is it likely that the HT "Spectrum Dynamics" series used an evolved form of the CT6000's sound engine?

I'm also curious about the "unique blip percussion IC "Hitachi HD61701" used in the CT6000. None of my other Casios have a rhythm section that sounds like the CT6000, it appears to be totally unique to the CT6000? Or were there any other models that used the same/ similar drums/ percussion as used in the CT6000?

At some point in the near future I'll dust down my CT6000 and see what I can do with it. I plan on attempting to compose, record and mix an entire song using only the CT6000 as a sound source, much the same as I did with my Casio SA-76. It will be interesting to see what I can come up with it.

[madtheory]

On 4/6/2020 at 7:33 AM, CYBERYOGI =CO=Windler said:

The HD61701 produces 24 lofi percussion sounds through 4 audio outs those are routed through external discrete filters to shape timbres.

Thanks from me too. I've deep-sampled my CT-6000. No limits on voice layering on Kontakt :). With 4 layers these sounds are reminding me of Wendy Carlos's work on the Tron soundtrack.  I'm going to try probing the board for the percussion sound, since I can only access a limited number by recording all of the patterns to find where sounds are isolated there.

 

On 6/13/2020 at 5:55 PM, Chas said:

At some point in the near future I'll dust down my CT6000 and see what I can do with it. I plan on attempting to compose, record and mix an entire song using only the CT6000 as a sound source, much the same as I did with my Casio SA-76. It will be interesting to see what I can come up with it.

I don't know if it would be great for a full track. I do find that syncing it to MIDI clock and sending it your basic chord progression is pretty fun. I step through the styles and find one that kinda fits. I usually edit the result in the DAW a bit. It's great for middle 8s and small diversions that you would not think of.

[pianokeyjoe]

Firstly, WOW CYBERYOGI! On point with the electronic details! I love it! Second, I have the CT6000. It uses the same sound synthesis method of the CPS201. This includes the Rhythm section. Now about the CT6500, I own 3 of them and the rhythm section(beats only) seem to sound similar to CT6000/CPS201. The CT6000/CPS201/CT6500 also used the MAIN VOICES as the Casio Chord voices though the CPS201(I have 3 of them too), uses ONLY the main voices for Casio Chord, so if you select harpsichord(my favorite on that model), the Chord is harpsichord too.. On the CT6000 and CT6500 you can mix and match. But the beats ARE a punchy Analog type sound. Cyberyogi explained it well.. filter arrays and voice mixing galore.

 

The Casio CT6000/CPS201 are kinda in the middle of a technological change and there were MORE models release with this sound gen like the uber rare CPS210(a CPS201 with midi),and a strange CT model that featured 73 keys and looked like the CT6500 but with velocity sensing keys(73 keys NOT 76!!).

[Steve Vernon]

I just picked one up last night for $50 that is fully functional and looks great. I'll address the scratchy volume control with some Deoxit this morning. Looking forward to playing it through an amp and possibly writing a song with it this weekend! 

[Szo]

I found one for sale in my country. Seller told that everything is working. price is $100 - what do you think?

[pianokeyjoe]

19 hours ago, Szo said:

I found one for sale in my country. Seller told that everything is working. price is $100 - what do you think?

If you have the money GRAB IT and RUN!! LOL!

[Chas]

On 2/18/2022 at 3:22 AM, Szo said:

I found one for sale in my country. Seller told that everything is working. price is $100 - what do you think?

 

Check the video in the first post as it gives probably one of the best demonstrations of the CT6000 sounds and capabilities (even though the thumbnail incorrectly describes it as Casio's only professional synth - the uploader HAS since acknowledged he made a mistake saying that.)

 

It's a very lush and thick sounding keyboard with some interesting options, though do bear in mind that it's from 1984 and is quite limited compared with newer keyboards. But if you like its unique sounds you'd be hard to pressed to find any another model that has the same sounds all in one package.

 

Also bare in mind that it is quite a large keyboard and it is HEAVY. Built like a tank too.

 

They used to be available for peanuts, but like all 80s vintage keyboards, prices have shot up in recent years. $100 is a good price in today's market, and also bare in mind that it has a (very well made and reliable) velocity AND after touch keyboard, AND it is equipped with midi, albeit a somewhat primitive/ basic form as it was also the first commercially available midi equipped Casio.

 

Unique and interesting sounds, and if you like what you hear and have the space, $100 is a very reasonable price for one of these today.

[disciple]

Did someone try to circuit bent this machine to control the filter or the lfo ? is it possible ?
thanks !

[pianokeyjoe]

Add the CPS101 to this list of keyboards that use the similar sound tech as the CT6000. The CT5500?? That one seems to be the same as the CT6500(PD Cosmo synth engine).

[Chas]

On 9/1/2023 at 7:38 AM, disciple said:

Did someone try to circuit bent this machine to control the filter or the lfo ? is it possible ?
thanks !

 

The CT6000 doesn't have a filter in the manner of a traditional analogue synth. It uses an advanced form of "Consonant Vowel" sound generation that is primarily digital in operation. There are some fixed filters used, but nothing comparable with a resonant analogue filter normally associated with classic analogue synths.

 

Same applies to the LFO. It likely has some clock circuits used for timing, but it does not use them the way a programmable analogue synth does. 

 

There are just a few hybrid Casios that have resonant analogue filters onboard. These are the HT/ HZ/ MT600 "Spectrum Dynamics" models, the MT400V and CT410V, and the FZ sampler series. The Spectrum Dynamics models and MT400V/ CT410V have well documented filter modifications that add external control for cut off and resonance, plus extending the resonance into self oscillation. To my knowledge, no one has modified the FZ filter, probably because it sounds so good and so unique as standard).