When an audio signal passes through a ring modulator, two so-called "side bands" are generated. These are copies of the input signal, linearly shifted in frequency by the frequency of the modulating oscillator symmetrically in both directions. Here, we used a ring modulator modulator frequency of around 300Hz, using a sine wave sweeping linearly from 160Hz to 2900Hz over a duration of around 2.3 seconds as input (first image). You can clearly see the two side bands in the second illustration (green lines, the red line shows the input signal and is overlaid for illustrational purposes only). As the two side bands are shifted linearly in frequency and harmonics in natural sounds are logarithmically distributed, a "metallic" or "hollow" unnatural sound is created – which can be used to great effect for processing voice.

A frequency shifter is essentially a ring modulator where one of the two side bands is suppressed, so that the signal is shifted in one direction only. This makes for an effect that takes up much less space in a mix than what you'd get with ring modulation. In practice, the amount of side-band and carrier suppression achieved varies between designs, in most cases it remains audible. This can be seen in the spectrogram below, where we used a well-known plug-in to shift frequency up by the same approximate 300Hz as in the ring modulator example above – the lower sideband is somewhat attenuated but still there.

Sufficient side-band suppression is, however, critical to achieving high quality frequency shifting and, more importantly, consistently useful results when shifting strongly. With signals that are of higher complexity than a sine-wave, this becomes even more true. Here, we have passed two swept sine-waves through the same well-known 3rd party frequency shifter, shifting down by 500 Hz. As you can see in the second image, the upper side-band is insufficiently suppressed, yielding a rather unclean result. Also note the lower of the two sine-waves appearing invertedly at the beginning of the sweep, this is due to the signal being shifted to below zero Hz and being "reflected" back up, a.k.a. aliasing. Both artifacts are displayed in orange for visibility.

With three swept sines – which is still a very simple signal compared to, for example, a voice – the problem gets worse. The below spectrograms show three swept sines, as well as the same three sines shifted by + 2000 Hz using the same 3rd party algorithm.

In comparison, WORMHOLE's frequency shifter is free of any aliasing, and has near-perfect side-band suppression, as evidenced by the spectrograms below – note the complete absence of the unwanted sidebands. Basically, the attenuation of the side-bands is so high that they fall outside of the spectrogram's displayed dynamics range. Audio-wise, this translates into a significantly cleaner sound and a much broader range of useful settings. 

WORMHOLE's WARP module behaves somewhat differently. The spectrograms below show the same sine sweep processed with a WARP DEPTH setting of 25%, 50%, 75% and 100%. Note how the structure of the output signal is noticeably more complex than with simple ring modulation or frequency shifting, while at the same time being much more "tidy" and sporting a more balanced distribution. The output is also free of any aliasing. Also note how the output components converge around the input signal with rising values for warp, resulting in a very defined, yet strongly processed sounding sound. 

By raising the POLES parameter, this convergence around the original signal's coordinates can be further increased, while at the same time introducing a series of resonance points, which tend to enforce the perception of a specific pitch, and which have sonic characteristics similar to a modal resonator, but with much less time-smearing. The below images illustrate this effect.

Finally, the TILT parameter applies processing somewhat similar to an unusually designed pitch/formant shifter – it shifts pronounced spectral features up or down. For simple input material the design of this circuit results in pitch-shift like effects, as can be seen in the below spectrograms, where the signal is rotated vertically (in frequency), while also moving up or down slightly. Note how TILT shows some aliasing coming in from the "top". TILT is intentionally designed to create grit for more extreme sounds.