Wackedpitchlfo; An Lfo Based Pitch Shifter - Kurzweil K2661 Musician’s Reference Manual

919 WackedPitchLFO

An LFO based pitch shifter.

PAUs: 3
Okay, it ain't pretty, but WackedPitchLFO uses LFO modulated delay lines with cross fades to produce a
shift of signal pitch. You can set the amount of shift in coarse steps of semitones or fine steps of cents
(hundredths of a semitone). This shifter works using the same concepts used to detune a sound in a chorus
algorithm. In a chorus algorithm, an LFO is used to change the length of a delay line. By smoothly
changing a delay line length from long to short to long, the signal is effectively resampled at a new rate
causing the pitch to rise and fall. In the WackedPitchLFO algorithm, the signal level is made to rise and
fall in time with the delay line movement so that we only hear signal from the delay line when the pitch is
rising (or falling). By overlapping and adding several delay taps moved by several LFOs, we can then
produce a relatively smooth pitch shifted signal.
Relatively.
It is possible for sounds coming out of the delay lines to be out of phase, which means that a certain
amount of cancellation can occur. The result sounds like there is a certain amount of tremolo in the pitch
shifted signal. The depth of the tremolo will depend on the pitch of the signal, the rate of the LFO and the
amount of pitch shifting—it will be different for every pitch. The rate of the tremolo is the rate of the LFO.
At higher rates the tremolo can be objectionable. At slow LFO rates, the pitch shifting is quite clean,
though you will hear some flanging. However longer delay line lengths are needed at slower LFO rates for
a given amount of pitch shift. The delays can get quite long, and it is possible to run out of available delay
(in which case you will get less pitch shift than you request). The trade-off is tremolo for delay. Higher
frequency signals will sound better when pitch shifted than lower frequency signals. Increasing the
amount of pitch shift will increase both the amount of tremolo and the amount of delay.
You can introduce feedback in WackedPitchLFO. When you do, the signal can be made to continuously
rise (or fall) as it repeatedly passes through the feedback loop.
The pitch shifter is based on delay lines. Changing the amount of pitch shift will produce large jumps in
delay line lengths, and you will hear the jumps as clicks if you are playing a sound while changing the
shift amount. For this reason, the shift amount parameters will not work well as modifiable parameters on
an FXMOD page.
Parameters:
Page 1
Wet/Dry -100 to 100 %wet
Feedback 0 to 100 %
LFO Rate 0.01 to 10.00 Hz
Lowpass 8 to 25088 Hz
Wet/Dry The relative amount of input signal and pitch shifted signal that is to appear in the final
effect output mix. When set to 0%, the output is taken only from the input (dry). When set
to 100%, the output is all wet.
Out Gain The overall gain or amplitude at the output of the effect.
Feedback By introducing feedback, the pitch can be made to continually rise or fall as the signal
makes successive passes through the pitch shifter.
Out Gain Off, -79.0 to 24.0 dB
Highpass 8 to 25088 Hz
Shift Crs -24 to 24 ST
Shift Fine -100 to 100 ct
KDFX Reference
KDFX Algorithm Specifications
10-187