A frequency shifter is a device that lowers or raises the frequency of an input signal. Engineers achieve this process by using a technique that involves complex amplitude modulation. This shifter does not maintain a harmonic relationship between the tones and the harmonics found in an input signal. Hence, all sounds that are processed by a frequency shifter sound quite unnatural. Regardless, it has been very practical for a long time and was widely popular in analog circuitries. Nowadays, the effects produced by frequency shifters are quite common.
Frequency Shifting
Frequency shifting, also known as single side-band modulation or SSB, is only able to produce either an upper or a lower spectral side-band. Since it only alternates the partials present within a sound, it is not capable of increasing their number. Because of this, the sound that emerges is quite hollow and smooth.
If the signal input is harmonic, the frequency shifter will modify the ratios of the partials. As a consequence, the sound is not harmonic. The sound remains the same if—and only if—the shift amount is equivalent to the frequency of one of the harmonic partials in the original sound. It’s impossible to determine if the frequency in a signal is positive or negative, but when a frequency is negative, it can transform itself into a positive one by simply flipping the sign. It’s essential that the user knows that downshifting might result in negative frequencies.
The Frequency Shifter and Plugins
Plugins are modern frequency shifter devices with similar controlling parameters, such as Coarse and Fine. Coarse and Fine parameters set the amount of the frequency shift. More complex plugin devices provide changes between the frequency shifting mode and the ring modulation mode. You can employ a wide parameter to create a stereo effect by simply inverting the spread value in one channel. Experts often use frequency shifting for tuning drum sounds and it’s an alternative to pitch shifting.
