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AlenK

Simulated Stepped Glissando

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Here’s a cool special effect that modifies a smooth pitch glide into a series of discrete steps. It depends on the ability of a solo-synth LFO to modulate one of its own parameters by way of a virtual controller. An example solo-synth tone file has been uploaded to the files area here if you would like to audition it or examine the patch for yourself. It should work equally well on both the XW-P1 and the XW-G1. Note that "glissando" has historically also meant a continuous pitch glide that in the synth world we almost always call "portamento."
 
(LFO1 is used here but you can choose LFO2 instead if you prefer.) First, choose a narrow pulse for LFO1: Puls1:3. Set its Rate initially to, say, 50 (you will adjust it later). Program a virtual controller with LFO1 as the source and the Rate of LFO1 as the destination. Use 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 has the direct effect of both narrowing the high excursion of the pulse waveform and widening its low excursion, reducing the pulse waveform’s duty cycle.

 

Program a second virtual controller with the output of LFO1 as the source and the portamento time of one or more of the pitched oscillators as the destination; choose S1-P2 to do all four internal pitched oscillators together. Enable portamento for the oscillators in question and set the portamento time (PortaTime) of each of them to a fairly high (and identical) value. Starting from zero decrease the depth value of the virtual controller (i.e., move it in the negative direction).

 

The more negative the depth the shorter the portamento time becomes during a very small portion of the period of LFO1. The rest of the time it will be very long. This results in an essentially stepped response that is almost (but not quite) the same as the pitch changes that occur during a true, stepped glissando.


With careful adjustment of the portamento time and the depth of the virtual controller modulating the portamento time, the desired glissando time between two notes can be achieved at the same time as the desired step size. For most musical purposes the step size should be a semitone or a whole tone (two semitones), but of course you can use whatever you like. Since both parameters affect step rate and step size at the same time some experimentation is in order.
 
The tables below show the important solo synth settings, including those of the virtual controllers, for a specific simulated glissando that produces steps of approximately a whole tone at a rate of about 20 steps a second. Note that all four of the solo synth’s internal pitched oscillators are assumed to be involved. The example audio file is the same except only one oscillator (Syn1) is turned on.
 
This technique doesn’t give the XW-P1 a true stepped glissando mode but it can nevertheless be useful (if difficult to configure!) as a special effect.

 

Block

Function

Sub-function

Parameter

Value

Syn1 – PCM2

 

 

Portamento

On

 

 

PortaTime

066

Oscillator

 

LFO1 Depth

000

LFO1

 

 

WaveType

Puls1:3

 

 

Sync

Off

 

 

Rate

107

 

 

Clk.Sync

---

 

 

Depth

067

 

 

Delay

000

 

 

Rise

000

 

 

Mod Depth

000

 

VC

Source

Destination

Depth

Purpose

1

LFO1

LFO1 Rate

+126

Shortens the pulse length

2

LFO1

Portamento Time (P1 – S2)

-128

LFO1 changes the portamento rate

 

This description of the technique is based on new content added to Revision 4 of The XW-P1 Companion, Volume 1

 

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