Frequency Shifter History
The origins of the Frequency Shifter go back to the early days of radio technology. Frequency shifting is related to ring modulation (RM): two signals are multiplied together, resulting in two so-called sidebands. One of these is the sum of all frequencies in both signals, the other is the difference. Unlike RM, frequency shifters output a single sideband, shifted down or up by a constant value. That’s why frequency shifters are sometimes called “Single Sideband Filters”.
Like RM, strong frequency shifting gives the signal a metallic character because all frequencies are shifted by a constant (e.g. 100Hz) instead of a factor (e.g. 2 times). For instance, when shifted 100Hz upward, 440Hz becomes 550Hz, while its octave (880Hz) becomes 980Hz (which is NOT an octave above 550Hz). Harmonic relationships are therefore destroyed by frequency shifting.
Frequency shifters are not only only suitable for special effects (e.g. horror-movie voices). Used in moderation, frequency shifting is similar to chorus or phasing, but without needing an LFO. While the pleasant beating of mildly detuned oscillators can become irritatingly fast when you play further up the keyboard, frequency shifting keeps this movement constant. Uhbik-S can synchronize beating to the song tempo.
There are similarities with phasing, as both cause a comb filter to move around the audio spectrum. The main difference is that movement in a frequency shifter is constantly downwards or upwards (like a barber’s pole). Phase cancellations that disappear out of the top will reappear at the bottom and vice versa. Also like a phaser, resonances can be accentuated via feedback.
Uhbik-S has been designed so that all negative side-effects are minimized or eliminated. Most other sideband filters have a poor frequency response – perhaps because the lowpass filter cutoff is set too low, just to be on the safe side. Also, a quality sideband filter needs either a high latency (e.g. for Hilbert transformation) or clever routines to prevent otherwise inaudible sidebands from folding back into the audible range.
Frequency shifters should never be confused with pitch shifters, which ideally leave the harmonic structure intact.
Shift and Frequency Range
The Shift knob controls the amount of frequency shift (down or up) relative to the value set by the Frequency Range switch. There are four “Hz” frequency ranges: 1 Hz, 10 Hz, 200 Hz and 4 kHz. The latter two are more suitable for extreme effects than for subtlety!
The frequency ranges 1/1 and 1/16 are not absolute values, they are factors relative to the current song tempo. An example: If the tempo is 120 bpm, 100% of 1/1 is equivalent to 0.5 Hz i.e. the modulation repeats every 2 seconds. Don’t be put off by this simple arithmetic - it will soon become second nature!
Uhbik-S also has a channel offset parameter for channel-independent animation (in this case frequency shifting). For instance, the phasing effect can continuously rise in one channel while continuously falling in the other.
Phase, Auto Reset and Manual Reset
Uhbik-S’s phase knob is a unusual for a frequency shifter. It adjusts the phase position of the frequency-shifted signal, with a range from zero to only one cycle (360°). Although the frequency shift has effectively disengaged the modulated signal from the dry signal i.e. they are out of phase anyway, it does open a few interesting doors...
Firstly, it lets you manually adjust the phase when detuning is zero. Secondly, it lets you set the position of a cyclic effect to e.g. the beginning of a bar (or any position you like).
With auto reset and manual reset, the phase of the effect signal can be synchronized to the dry signal. A click on manual reset to instantly reset the phase. The auto reset button automatically resets whenever the signal level drops below a (very low) threshold.
Feedback works like phaser feedback i.e. it increases cancellation as well as resonance. Remember that extreme feedback can lead to self-oscillation.
Sets the relative volumes of the dry and wet signals. The maximum value (100.00) is suitable for special effects such as robot voices, while the center position (50.00) is best for phasing.