I love me some good snark, especially when you come across it in synth manuals, as I did when I was reading up on Xaoc Device's Koszalin, their new “Stereo VC Frequency Shiftor Model of 1964,” and stumbled upon a pretty good gem describing the difference between pitch shifting and frequency shifting:

"A common fallacy says modulation is the same as adding and subtracting signals, which is complete nonsense since multiplying is not adding and subtracting."

I like when people call something nonsense. It’s funny. Xaoc Devices, whose module names I find slightly humorous to begin with, is definitely flashing a bit of moxie, and they should. Koszalin is a great module, and the difference between pitch shifting and frequency shifting is important. To be certain, Kos is not a pitch shifter, it’s a frequency shiftor. They even spell it “shiftor” and not “shifter,” if there was any doubt. But how is frequency shifting different than pitch shifting? This, again from the Koszalin manual:

“If the input is a periodic waveform with a 1kHz frequency, it usually contains the 1kHz component plus the harmonic overtones: 2kHz, 3kHz, 4kHz, etc. When this signal is shifted by 200Hz the result contains 1.2kHz, 2.2kHz, 3.2kHz, 4.2kHz, etc. That means the new components are no longer multiples of the first frequency. Pitch shifting…results in scaling the frequencies by the same factor. Applying a factor of 1.2 would net a signal that contains 1.2kHz, 2.4kHz, 3.6kHz, 4.8kHz, etc.”

The most important thing to know is that frequency shifting can get WAY more freqy than pitch shifting. As described above, frequency shifting changes the incoming sound's harmonic structure and yields unique ring-mod-ish sounds, and Kos does this in stereo and is able to turn a simple input into something extraordinary.
Overall, the frequency of the input signal/s can be altered by +/-5kHz and Kos has two inputs, L and R, and four outputs; one stereo pair of Upshifted Outputs, and one stereo pair of Downshifted Outputs. They way the signal/s is/are manipulated is through the feedback path and there are inputs for Through-Zero Frequency Modulation [TZFM], and Exponential Frequency Modulation, the former which has a trimmer pot attenuator. There are also controls for Density and Regen[eration] with modulation inputs for those and a small Range switch to multiply the frequency by 1, 10, and 100. The Regen also has a switch to select between downshifting, upshifting, or both. The giant Shift knob that takes center stage on the module sets the amount of frequency shifting that is applied to the signal/s. The Shift knob is off in the center position [0Hz] and is exponential in response on both sides of 0.
When I started patching this up I wasn’t sure what to expect. I’ve no experience with a frequency shifter, and plenty with a phase or pitch shifter, so I was somewhat surprised to see that it’s kind of similar to both of those, and not similar at all. I mean, it warps, tweaks, and well…shifts your signal, and can sound similar to a phase shifter, but once you get Kos all patched up—both inputs and all four outputs along with the modulation opportunities—the sonic differences become more pronounced.
In terms of modulating the signal, the linear TZFM input tended on more on the subtle side of things and patching a sine wave into it and attenuating it with the onboard control made for some nice mellow, pronounced shifting, while the Exponential FM input was a bit less predictable and had the propensity to be unruly, depending on what you threw into it. A random LFO at full strength went gangbusters on a simple melodic input, especially when the shifting switch was in the Both position.
With just a simple input you can get everything from phase shifting sounds to bubbly warbles to alien raygun weirdness to indescribable wack. While it’s easy to see a lot of traversing too much into the aforementioned indescribable wack territory, Kos also excels at subtle beauty. By design it’s easy to both maintain and lose control in Kos, the latter done by patching in some CV into Regen or Density to conduct rapid changes, but it’s not a module that you get lost in to a point of no return. It’s surprising how much mileage can be had just by using one or two of the four CV modulation options available. Though the shifting options switch doesn’t have a CV input so it too can be modulated, by patching any of the outputs into a crossfade/panning module you’re able to switch things that way up to get even crazier soundscapes, and that’s really were Kos’s biggest strength is; the ability to mix and match the four outputs.
Along with the multiple outputs, one of the main features of Koszalin is how much control you have over the feedback path going to each channel. Tweaking or CVing the Regen and Density really lets you explore and hone in the detail of the feedback with the ability to craft and control. Or not control. Sometimes I’d be a’ patching and the sound would go off the rails. Subtle or wack [I love the word wack], Kos has a lot going for it. Just don’t call it a pitch shifter.

10 HP +12v 140mA -12v 30mA
Price: $349

xaocdevices.com