Video notes: VZ-1 "phase" mode is wavefolding
2025-06-15
In this post I reflect on what I learned from making this Youtube video: "The Casio VZ-1 does not do FM - it does wave folding".
What is in the video?
A still image from the video
I have previously written about the Casio VZ-1. It is an obscure and poorly understood synthesizer from 1988. Deep inside an internet forum discussion, synthesizer expert acreil figured out what is really going on inside this machine. For some reason I have taken it upon myself to try and make this information more visible. My latest video is part of that effort.
One of the basic misconceptions some people have about the VZ-1 is that it somehow does FM synthesis like the Yamaha DX7. This is incorrect; it does wavefolding. While the underlying technology is similar (you coud call it "creative use of sine wave lookup tables"), the VZ-1 carefully avoids Yamaha's FM synthesis patents.
The part that people confuse with FM is the "phase" mode of the VZ-1. In the video I show how "phase" mode interacts with oscillator pitch, amplitude and with the basic waveforms of the VZ-1.
If you're mathematically minded, the difference is that Yamaha FM is roughly the sound ofsin(x + sin(y)), and the Casio VZ "phase" wavefolding issin(sin(y)). Both of these have harmonic spectra with coefficients determined by Bessel functions, which might be why their timbres can sound similar?
Camera position
I find camera positioning difficult as it is and this video added a new challenge in the form of the oscilloscope. In my previous videos my biggest concern was being able to read what is on the synthesizer display. Then in addition to that, I want to show as much of the user interface (buttons, sliders) as possible so that you can see what I'm doing. This time the oscilloscope was as important as the display and I mostly gave up on showing the buttons.
Both the oscilloscope and the synth display have a limited viewing angle so I had to work out a way to get the camera as close as possible to the position where my head would naturally be.
The camera setup for the video. Note the extra light on the left that I use to suppress reflections on the synth display. The camera itself is missing because it's my phone and I'm using it to take this picture. You do see the camera mount the phone clicks into.
Oscilloscope wrangling
Getting a stable picture out of the oscilloscope when playing a sine wave is relatively easy because a sine wave has just one peak. But then when I start changing settings on the synth to produce wave folding, I'm in trouble because now there are multiple peaks. The only control I had to deal with this was changing the volume of the audio.
As long as one peak is slightly higher than the others, if I turn down the volume so that only the highest peak passes the trigger threshold then the picture becomes stable. If I turn the volume down too much the picture becomes a blur. If it's too high you get a superposition of phase-shifted versions of the waveform.
The peaks keep changing as I change the synth settings so I had to constantly adjust the volume to make the oscilloscope pitcture look good. This was not ideal; there are times in the video where nothing happens but me fighting the oscilloscope.
One solution for this problem is to run a secondary signal into the oscilloscope, that is itself stable, and phase-locked to the interesting signal. If you then configure the oscilloscope to trigger on the secondary signal then the primary signal remains stable on the screen, no matter how weird it gets. Looking back, I suspect I can make this work on the VZ-1 if I create a layer sound, route the layers to separate audio outputs, trigger from the second layer and do the demonstration on the first layer. I don't know though if the synth would still play the second layer while you're editing the first.
Another thing I could have done now that I think about it is edit out the bits where nothing happens but me fighting the scope.
One last funny problem with the oscilloscope is that there are bright LED's in the user interface. This was creating too much contrast for the camera and ended up looking very distracting. I fixed the problem by putting a black piece of cloth on top of the part of the scope that has the bright lights.
Did I learn anything new about the VZ-1?
I don't think I learned anything new that I did not already know by ear but it is nice to get a visual from the oscilloscope.
I say now that it's nice but I actually have mixed feelings about it. I don't like looking at oscilloscopes and other audio visualizers when working on music and sound design because it feels like my brain becomes preoccupied with the visual information while my goal is to make something sounds good.
Back to the VZ-1. It's nice to see that sending a sine wave into a "saw5" wavefolder really creates a square wave. It's not a perfect square wave but by synthesizer standards it is a very natural square wave shape.
Besides sine waves, the VZ-1 oscillators can create a kind of warped sine wave that looks like a sawtooth. The "saw5" wave is the sharpest quasi-sawtooth.
The square wave you get by sending a sine wave into a saw5 wavefolder at minimum amplitude.
What is so frustrating about this, and I already knew this, is that you cannot dynamically "soften" this square wave on the VZ-1. On a subtractive synth you can take the (literal) edge of this square wave with a lowpass filter, and if this was made with FM you could lower the modulation index. But on the VZ-1 this square wave is the mellowest thing you get. You can only increase the amount of folding, making it harsher.
If you change the wavefolder wave shape from "saw5" to "saw4", ..., "saw1" or "sine" you get mellower sounds of course but you can't do that dynamically. So this cool saw5 square wave is kind of useless because I rarely like listening to such bright saw waves without a mellowing effect like a lowpass filter.
Conclusion
I'm glad I made this video because as nerdy and obscure as it is, I care about this subject and I want to share what I have learned with a wider audience. Video is a good medium for that.
Adding the oscilloscope was essential for the concept of the video but also challenging because (1) it complicates the cinematography and (2) I'm not an experienced oscilloscope user. That is a good thing because it means I got to learn more from making this video.