Hello, all.
Recently, I have been trying to recreate some of my favorite Casiotone patches on the Shruthi with mixed success. Casiotone Consonant Vowel Synthesis is simply composed of two square-type waves which are independently mixed together. This process happens in three major steps – two of which the Shruthi already supports.
1: Create a square wave or multipulse square wave
This can be achieved by simply using the default square wave generator.
To emulate multipulse style waves, simply sync the two waves with the second oscillator being a higher pitch than the first one. Adjusting the PWM on the second oscillator also changes the timbre more in line with what a Casiotone could do.
2: Mix the two waves together using independent envelopes
While the Shruthi does not have two independent envelopes for the amplitude of each oscillator, it is easy to change the relative volumes of each one by assigning an envelope to the “mix” parameter in the modulation matrix.
3: Filter the two square waves independently
This is the one stumbling block. The Shruthi only has one filter. However, if it were possible to create a new square wave generator that featured the one pole filter on the noise oscillator, it would be possible to achieve the proper tone – the Casiotone.
Why is the filter on the square wave necessary?
Simply put, most Casiotone presets started with an unfiltered/less filtered multipulse pluck of sorts before settling down into a more conventional square wave that had its upper harmonics slightly dampened by a low-pass filter.
Adjusting the filter on the Shruthi dampens the second wave, but it takes all of the “pluck” out of the multipulse. That is the main problem.
Here are some ways that I tried to troubleshoot the problem.
1: Use a different wave for the first oscillator
Obviously, this one works depending on the kind of patch. I found that the formant simulations as well as the “res3hp” waves worked great for certain PWM settings, but nothing too close.
2: Use an external square wave with a low-pass filter
I used my JX8P for this test. It works well up to a point.
First off, changing the volume envelope on the Shruthi changes the amplitudes of both the internal and external waves.
Second, if you turn off the first oscillator to use the “mix” parameter as the “envelope” for the internal wave, you then lose the sync sound of the second oscillator.
Here are my possible firmware solutions, starting with the most difficult to implement.
1: Add the filter from the noise oscillator to the square wave generator. Creating a new oscillator.
2:Change the firmware so that when oscillator one is set to “none” the second oscillator can sync to the internal clock of the synthesizer. Similar to how sync works on the JX8P. (You can turn the wave off and it will still function properly because there is a digital clock that controls the tuning of the first oscillator.)
This would be the best solution as it requires 0 changes to how many parameters a patch has to store. However, an external square wave is then necessary.
3: Make a custom wave table. I could always make a wavetable from my Casiotones, but I was hoping to explore new timbres.
I figured that I would go ahead and post this information because of the inclusion of the Casio CZ series waves. Having the ability to do Consonant Vowel Synthesis on the Shruthi only seems to make sense. I also hope that other Casio lovers will find this information useful when trying to recreate Casiotone patches of their own on the Shruthi or other synthesizers.