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Simulated Sample-and-Hold

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Here’s a little trick to simulate a sample-and-hold effect using the solo-synth LFOs. A sample-and-hold LFO waveform changes in discrete steps rather than continuously (see the diagram below). This works on both the XW-P1 and the XW-G1. A working example you can load into your XW synth is available here.


This technique uses both LFOs. First, choose a narrow pulse for LFO1: Puls1:3. Set its Rate initially to, say, 50 (you will need to adjust it later). Choose either Sin, Tri, SawUp or SawDown for LFO2 and set its rate to zero (the posted example uses Tri). Program a virtual controller with LFO1 as the source and the Rate of LFO1 as the destination, with a positive depth. This sets up a positive feedback loop that speeds up LFO1 when its signal is high and slows it down when its signal is low. This narrows the high excursion of the pulse waveform and widens its low excursion, reducing the pulse waveform’s duty cycle. (Yes, this is the same trick used in the simulated stepped glissando technique that I posted yesterday.)


As the depth of the virtual controller increases both the pulse width and the frequency of LFO1 decrease. Adjust the frequency of LFO1 and the depth of the virtual controller to achieve as narrow a pulse as possible at the rate of "sampling" you desire. (You can temporarily modulate the pitch of an oscillator with LFO1 to audition the effect.)


Program a second virtual controller with LFO1 as the source and the rate of LFO2 as the destination. As you increase the depth of this virtual controller the output of LFO2 will transform, changing from the sine, triangle or sawtooth wave that the LFO normally produces to a discretely stepped version of it. This happens because the output from LFO2 changes very slowly when LFO1 is low during most of its period and then changes very quickly during the very brief time that LFO1 is high. You will need to decrease the Rate of LFO2 as you increase the depth of the virtual controller to maintain a given frequency. 


While this technique does not create a perfect sample-and-hold effect it is audibly quite close and distinctly different than the Random waveform, which also produces a stepped output.



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