I was playing with one of Rob's patches called SynthT-Bell. Very very cool ring mod effect, just the type of thing that makes me giddy. I started to strip it down & move the modules around in an attempt to understand it. But, it's one of those mysterious patches that processes the Master/Slave signal in weird ways, so I'm at a loss. I did manage to modify it and end up with the attached version, which mostly replaces the manual timbre control with an LFO sweep.

It may be asking too much to explain the patch in an email, but if you're in the mood, Rob, how about a brief lesson? If I can figure this out, I'm sure I'll be using these ideas a lot.

Ringmod works nice if the two frequencies have a nice harmonic relation, just like with FM. To get a knobcontrol that has such relations at most knobsettings one needs linear frequency control. The Pitch and FMA knobs however have logarithmic control, which results in most knobsettings giving enharmonic sounds. The grey signal is basically a V/Hz control signal which means that if one controls this signal with a linear knob like on the Control mixers, you get a control where e.g. settings 8, 16, 24, 32, 49, etc. result in a nice exact harmonic relationship.

Doubling the grey signal means a raise of frequency by one octave, which you get when you feed a grey signal to the two inputs of the Control mixer (1 + 1 = 2). Setting the Control mixer to linear and controlling only one knob gives 128 ratios for the 128 knobsteps. These are 128:128, 129:128, 130:128, 131:128 up to 256:128. Between these are the nice ratios of 160:128 which becomes 5:4, 196:128 which becomes 3:2, also 7:4, 9:8, 11:8 etc. are present. So we get 128 very usable ratios within one octave. Multiplying the signal on the input that is used to set the ratio by four means that the 128 steps are nicely spread over the ratio 1:1 till 5:1, so the fifth harmonic. It goes like 128:128, 132:128, 136:128, etc.

As 128 is an even number the ratios 4:3 and 5:3 can only be approximated to knobsettings 43 and 85. But these are about the only simple ratios that need a little twist on the Fine knob.

RM to be played on the keyboard in tune with other instruments works the easiest if the frequency ratio is very simple, like 3:2, 4:3 or 5:4, but the waveform has a complex harmonic content. E.g. squarewaves work notably well. If the two oscillators drift a little the sound gets easily out of tune and the pitch might have to be carefully retuned, which is difficult with slightly enharmonic sounds. The control mixer trick simply keeps the sound much easier in tune with others.

In the example patch knob1 of the control mixer of the left two oscillators gives virtually beatfree sounds for every eight steps. On the middle example the beatfree sounds are not regularly spread on their knobs. Modulating is done by multiplying the grey signal with the modulation signal and again adding it to the grey signal. E.g. in the third row the grey signal is modulated by a quantized LFO. If the quantize stepsize is eight the modulation results in a number of ratios of 128:128, 144:128, 160:128, etc. There is also 112:128, 96:128, etc. The quantizer range sets the modulation depth.

And the same trick can be used to get some more fine control over slave LFOs, great if you want to create patterns by combining two detuned LFO sources.

Many analog synths were V/Oct but some were V/Hz, like the Yamaha CS50 I once used. V/Oct is very versatile on standard 12 notes in an octave tuning. V/Hz has its own tricks, notably when going through harmonic series, which is interesting for more exotic tuning systems. Basically those tunings can be thought of as sets of some simple frequency ratios, e.g. the Pythagorean tuning.

Well, there is a lot behind it. But its a simple thing to patch and works very conveniently for me.

What I would really like to have on the NM is a module that can do these ratios by setting a multiplier value and a divisor value. This module should operate on the grey signal. Making other tuning systems would then be very simple. We would also need a controllable switch to choose between the set ratios. Or maybe that would be integrated, e.g. a module where one can set a number of ratios, one for every note number.

Oh, wait... in the patch it is not only RM but some FM trick added as well. The RM tuning is as usual, but by adding a certain amount of the first oscillators outputsignal to the grey value the timbre can be made more bright without loosing tuning. Multiplying the output with the grey value gives less brightness but timbre tracking over the keyboard.