Rob Hordijk Triple LF-VCO: Difference between revisions

Jump to navigation Jump to search
Content added Content deleted
VisualWikitext
(Added links, more images, and a huge amount of content from the Hordijk Blog. Still doing a lot of editing and rewriting for clarity and simplicity.)
(→‎Internal Normalisations: - added a new connection)
 
(4 intermediate revisions by the same user not shown)
Line 1: Line 1:
[[File:Hordijk trilfo.png|thumb|200px|Panel design for a Rob Hordijk TRIPLE LF-VCO]]The '''Rob Hordijk Triple LF-VCO''' contains three independent CV controllable LFO's or as Rob calls them LF-VCO's.
[[File:RobHordijk-TriLF-VCO.jpg|thumb|Photo of a Rob Hordijk LF-VCO. (Photo by Todd Barton)]]The '''Triple LF-VCO''' is a module by [[Rob Hordijk Design|Rob Hordijk]] it contains three independent CV controllable LFO's or as Rob calls them LF-VCO's. The modulation inputs of all VC-LFO's are normalized at the input connectors in such a way that everything can crossmodulate and sync.<ref name="rh">Rob Hordijk</ref> Each LF-VCO also has an LED to provide visual feedback.

The modulation inputs of all VC-LFO's are normalized at the input connectors in such a way that everything can crossmodulate and sync.<ref name="rh">Rob Hordijk</ref>

Each LF-VCO has an LED to provide visual feedback.


=== LF-VCO A ===
=== LF-VCO A ===
'''LF-VCO A''' provides a sine wave output, with inputs for frequency modulation (A MOD) and 'fluctuation' (A FLUCT).
'''LF-VCO A''' provides a sine wave output, with inputs for frequency modulation (A MOD) and 'fluctuation' (A FLUCT). There are knobs to control frequency (LF-VCO A RATE), frequency modulation depth (LF-VCO A MOD), and fluctuation depth (LF-VCO A FLUCT). Fluctuation is a combination of AM and FM that soft-syncs to the harmonics of the modulating signal, providing a more 'natural' feel for things such as vibrato than a traditional LFO even at high frequencies.<ref name="rh" /> '''LF-VCO A'''<nowiki/>'s frequency modulation input is normalised to '''LF-VCO C's S/H output. '''

There are knobs to control frequency (LF-VCO A RATE), frequency modulation depth (LF-VCO A MOD), and fluctuation depth (LF-VCO A FLUCT).

Fluctuation is a combination of AM and FM that soft-syncs to the harmonics of the modulating signal, providing a more 'natural' feel for things such as vibrato than a traditional LFO even at high frequencies.<ref name="rh" />

'''LF-VCO A'''<nowiki/>'s fluctuation modulation input is tied internally to '''LF-VCO C.''' <!-- Regular or inverted wave? -->


=== LF-VCO B ===
=== LF-VCO B ===
'''LF-VCO B''' provides triangle and pulse wave outputs, which are uni-polar; and inputs for frequency modulation (B MOD) and synchronisation (B SYNC/HALT).
'''LF-VCO B''' provides triangle and pulse wave outputs, which are uni-polar; and inputs for frequency modulation (B MOD) and synchronisation (B SYNC/HALT). There are knobs to control frequency (LF-VCO B RATE), frequency modulation depth (LF-VCO B MOD), and waveform shape (LF-VCO B SHAPE). The frequency range goes from several minutes to around 100Hz, and has a slower range than LFO A. The triangle output can be modulated from ramp to triangle to saw (like the Korg MS20). The wave shape control also effects the pulse width.

There are knobs to control frequency (LF-VCO B RATE), frequency modulation depth (LF-VCO B MOD), and waveform shape (LF-VCO B SHAPE).

The frequency range goes from several minutes to around 100Hz, and has a slower range than LFO A.

The triangle output can be modulated from ramp to triangle to saw (like the Korg MS20). The wave shape control also effects the pulse width.


'''LF-VCO B''' has a switch to select between hard-sync or a "stop" function. The stop function stops the LFO on the current output level and from that it goes further on the rhythm of a modulating input signal or the triangle LF-VCO.<ref name="rh" /><!-- This feels poorly explained - need to clarify. -->
'''LF-VCO B''' has a switch to select between hard-sync or a "stop" function. The stop function stops the LFO on the current output level and from that it goes further on the rhythm of a modulating input signal or the triangle LF-VCO.<ref name="rh" /><!-- This feels poorly explained - need to clarify. -->

'''LF-VCO C'''<nowiki/>'s frequency modulation input is tied internally to '''LF-VCO C. <!-- Regular or inverted wave? -->'''
⚫
[[File:TriLFO flowchart.jpg|thumb|TRIPLE LF-VFO flowchart]]
[[File:TriLfoSH flowchart.jpg|thumb|TRIPLE LF-VFO flowchart.]]



'''LF-VCO B''' has three operating modes, selectable with a switch: <ref name=":0">[https://thehordijkmodular.blogspot.com/search/label/Triple%20LF-VCO LF-VCO] by Benoit Faivre (2018)</ref>
'''LF-VCO B''' has three operating modes, selectable with a switch: <ref name=":0">[https://thehordijkmodular.blogspot.com/search/label/Triple%20LF-VCO LF-VCO] by Benoit Faivre (2018)</ref>

* SYNC (up) : '''LF-VCO B''' is synced to '''LF-VCO C''' or to an external signal
* SYNC (up) : '''LF-VCO B''' is synced to '''LF-VCO C''' or to an external signal
* MODE (center) : '''LF-VCO B''' is free running
* MODE (center) : '''LF-VCO B''' is free running
Line 37: Line 15:


=== LF-VCO C ===
=== LF-VCO C ===
'''LF-VCO-C''' provides triangle and inverterd triangle wave outputs.
'''LF-VCO-C''' provides triangle and inverterd triangle wave outputs. The frequency range goes from several minutes to 100&nbsp;Hz.<ref name="rh" /> There are knobs to control frequency (LF-VCO RATE) and frequency modulation depth (LF-VCO C MOD).


⚫
[[File:TriLfoSH flowchart.jpg|thumb|TRIPLE LF-VFO flowchart with new Sample and Hold function.]]
The frequency range goes from several minutes to 100&nbsp;Hz.<ref name="rh" />


=== Sample & Hold Function ===
⚫
In new versions the modulation input of '''LF-VCO C''' has a S&H right after the input connector, but just before the input level knob. '''LF-VCO C''' triggers the S&H circuit.


The S/H is triggered every change of direction (rising to falling, or falling to rising)


⚫
On every positive peak and on every negative peak of the triangle waveform the S&H samples the '''LF-VCO C''' modulation input signal and holds the sampled value during the slope that follows. This means that the S&H causes every up-slope and every down-slope of the triangle to have a different duration, defined by the momentary value the S&H happened to sample. The slopes remain perfectly linear, only their steepness is affected. The effect is that there is a more or less random spread in time. This also effects the duration or width of the pulse output.
The LF-VCO C Mod slows down the rate of the falling slope of the triangle. The rate of the rising slope remains the same. For example, when speeding up the LFO and opening the C MOD knob the out-put will have a fast attack and slow decay envelope like a saw-tooth wave.


The pulse output goes high while the slope is rising and low when falling, so the pulse length will remain the same but the time between the pulses will increase.<ref name=":0" /> <!-- This feels contradictory. Need to clarify. -->
In old versions the '''LF-VCO C''' Mod would slow down the rate of the falling slope of the triangle, while the rate of the rising slope remained the same. For example, when speeding up the LFO and opening the C MOD knob the out-put will have a fast attack and slow decay envelope like a saw-tooth wave. The pulse output goes high while the slope is rising and low when falling, so the pulse length will remain the same but the time between the pulses will increase.<ref name=":0" /> [[File:TriLFO flowchart.jpg|thumb|TRIPLE LF-VFO flowchart]]<!-- This feels contradictory. Need to clarify. -->


Regrettably this self-modulation feature is obsolete as Rob developed a S&H instead.




⚫
Note for frequency modulation: A high frequency can easily be deeply modulated by a low rate, but a low frequency is much harder to modulate deeply with high frequency. A S&H changes this FM equation into a pure statistic function that becomes pitch independent, resulting in slow rates reacting much deeper to faster rate modulation signals as without the S&H. For example, when a 1Hz LFO is modulated with a 1kHz signal there may only be a tiny bit of 1kHz zippery noise in the LFO signal, but the 1Hz will not seem to change much. But by using a S&H on the 1Hz LFO it will instead go all over the place, defined by the average amplitude of the 1kHz signal.
Here is Rob's description about it:

⚫
The modulation input of LFO C has a S&H right after the input connector, but just before the input level knob. LFO C triggers the S&H circuit.

⚫
On every positive peak and on every negative peak of the triangle waveform the S&H samples the LFO C modulation input signal and holds the sampled value during the slope that follows. This means that the S&H causes every upslope and every downslope of the triangle to have a different duration, defined by the momentary value the S&H happened to sample. However, the slopes will remain perfectly linear, only their steepness is affected. The effect is that there is a more or less random spread in time. On the pulse output this causes pulses of different duration, an effect also named clustering in time.


⚫
To use the S&H modulation on LFO C it is often a good idea to not set the LFO C rate knob to its maximum. While there are not set limits for the minimum rate times, a very large negative modulation signal can cause a LFO to stop oscillating. If this happens when the LFO C rate knob is at its minumum, the modulation level knob is fully open, and a sampled negative signal is stopping the LFO, and thus also not sampling a new value that can start it again. In this case LFO C may appear to be frozen. In that case you can just open the rate knob a bit until it starts oscillating again. Or wait for a very long time for the S&H capacitor to eventually loose its charge.<ref name=":0" /> [[File:Hordijk trilfo.png|thumb|200px|Panel design for a Rob Hordijk TRIPLE LF-VCO]]
=== Internal Normalisations ===
=== Internal Normalisations ===
Many of Rob's designs feature internal connections or 'normalisations' between inputs and outputs. These can be broken by inserting jacks into the inputs. When found together in triple-module formation the following normalised connections were made:
The output of the S&H is only available internally, but also normalizes to the LFO A modulation input. This can be overridden by inserting a jack with another signal into the LFO A modulation input. When no jack is connected to this LFO A input it will follow the S&H on the LFO C modulation input.
[[File:RobHordijk-TriLF-VCO.jpg|thumb|Photo of a Rob Hordijk LF-VCO. Photo by Todd Barton]]
When no signal is inserted in the LFO C modulation input it is normalized to the output of LFO A. This means that when no jacks are applied to the LFO A and LFO C inputs, but their input level knobs and the LFO A fluctuation knob are opened, the result is constantly varying pitches and rates on both LFO A and LFO C, caused by the crossmodulation between LFO C and LFO A. On LFO A it will always sound like a stepped pattern unless you also open the fluctuation knob, as that will modulate the pitch slightly with the slopes of LFO C or with an external signal when the fluctuation input has a jack with a signal plugged in.

⚫
Note that for pitch or frequency modulation there is a behaviour that a fast pitch can easily be deeply modulated by a slow pitch or rate, but a slow pitch or rate is much harder to modulate deeply with a much faster pitch. A S&H changes this FM equation into a pure statistic function that becomes pitch independent, resulting in slow rates reacting much deeper to faster rate modulation signals as without the S&H. E.g. when a 1Hz LFO is modulated straightforward with a 1kHz audio signal there may only be a tiny bit of 1kHz zippery noise on the LFO signal, but the 1Hz will not seem to change much. But through the S&H the LFO will instead go all over the place, defined only by the average amplitude of the 1kHz signal.

⚫
There are maximum possible pitches for the three available LFO’s, they basically can not go faster as the maximum setting on their rate knobs. To use the S&H modulation on LFO C it is often a good idea to not set the LFO C rate knob to its maximum. There is not such a limit for the minimum rate times, though a very large negative modulation signal can cause a LFO to actually stop oscillating. If this happens when the LFO C rate knob is at its minumum, the modulation level knob is fully open, and a sampled negative signal is stopping the LFO, and thus also not sampling a new value that can start it again. In this case LFO C may appear to be frozen. In that case you can just open the rate knob a bit until it starts oscillating again. Or wait for a very long time for the S&H capacitor to eventually loose its charge.

A tip is to e.g. apply the LFO C Pulse output to the S&H input of one of the EnvGens while clocking that EnvGen with a stable clock. Then feed the output of that S&H to the Gate input of the second EnvGen. While the first EnvGen is triggered at a stable rate the second will trigger only now and then in an irregular rate but synced to the clock of the first EnvGen. If LFO C is deeply modulated the second EnvGen gates seem to appear in clusters in time.


* LF-VCO - C S/H (internal) > LF-VCO A Modulation input
And there are many other uses if you want to introduce a smaller or larger amount of variation in dynamics to an otherwise static pattern, or to spread events unevenly in time.<ref name=":0" />
* LF-VCO - C TRIANGLE output > LF-VCO A Fluctuation input
* LF-VCO - A SINE output > LF-VCO C Modulation input
* LF-VCO - B PULSE output > DUAL ENV - GATE IN


This means that when no external signals are applied to the inputs, and their modulation input level knobs are opened, LF-VCO A and LF-VCO C cross-modulate one another.<ref name=":0" />
== External Links ==
== External Links ==


Latest revision as of 23:59, 19 June 2022

Photo of a Rob Hordijk LF-VCO. (Photo by Todd Barton)

The Triple LF-VCO is a module by Rob Hordijk it contains three independent CV controllable LFO's or as Rob calls them LF-VCO's. The modulation inputs of all VC-LFO's are normalized at the input connectors in such a way that everything can crossmodulate and sync.[1] Each LF-VCO also has an LED to provide visual feedback.

LF-VCO A

LF-VCO A provides a sine wave output, with inputs for frequency modulation (A MOD) and 'fluctuation' (A FLUCT). There are knobs to control frequency (LF-VCO A RATE), frequency modulation depth (LF-VCO A MOD), and fluctuation depth (LF-VCO A FLUCT). Fluctuation is a combination of AM and FM that soft-syncs to the harmonics of the modulating signal, providing a more 'natural' feel for things such as vibrato than a traditional LFO even at high frequencies.[1] LF-VCO A's frequency modulation input is normalised to LF-VCO C's S/H output.

LF-VCO B

LF-VCO B provides triangle and pulse wave outputs, which are uni-polar; and inputs for frequency modulation (B MOD) and synchronisation (B SYNC/HALT). There are knobs to control frequency (LF-VCO B RATE), frequency modulation depth (LF-VCO B MOD), and waveform shape (LF-VCO B SHAPE). The frequency range goes from several minutes to around 100Hz, and has a slower range than LFO A. The triangle output can be modulated from ramp to triangle to saw (like the Korg MS20). The wave shape control also effects the pulse width.

LF-VCO B has a switch to select between hard-sync or a "stop" function. The stop function stops the LFO on the current output level and from that it goes further on the rhythm of a modulating input signal or the triangle LF-VCO.[1]

LF-VCO B has three operating modes, selectable with a switch: [2]

  • SYNC (up) : LF-VCO B is synced to LF-VCO C or to an external signal
  • MODE (center) : LF-VCO B is free running
  • HALT (down) : LF-VCO B's frequency is set by its RATE control, but during the rise of the Triangle wave of LF-VCO C and will "freeze" during the Fall of the Triangle wave of LF-VCO C. LF-VCO B will restart with the next cycle of LF-VCO C. When "frozen", LF-VCO B will output a fixed, momentary voltage. Halt mode works best on pitch.

LF-VCO C

LF-VCO-C provides triangle and inverterd triangle wave outputs. The frequency range goes from several minutes to 100 Hz.[1] There are knobs to control frequency (LF-VCO RATE) and frequency modulation depth (LF-VCO C MOD).

TRIPLE LF-VFO flowchart with new Sample and Hold function.

Sample & Hold Function

In new versions the modulation input of LF-VCO C has a S&H right after the input connector, but just before the input level knob. LF-VCO C triggers the S&H circuit.

The S/H is triggered every change of direction (rising to falling, or falling to rising)

On every positive peak and on every negative peak of the triangle waveform the S&H samples the LF-VCO C modulation input signal and holds the sampled value during the slope that follows. This means that the S&H causes every up-slope and every down-slope of the triangle to have a different duration, defined by the momentary value the S&H happened to sample. The slopes remain perfectly linear, only their steepness is affected. The effect is that there is a more or less random spread in time. This also effects the duration or width of the pulse output.

In old versions the LF-VCO C Mod would slow down the rate of the falling slope of the triangle, while the rate of the rising slope remained the same. For example, when speeding up the LFO and opening the C MOD knob the out-put will have a fast attack and slow decay envelope like a saw-tooth wave. The pulse output goes high while the slope is rising and low when falling, so the pulse length will remain the same but the time between the pulses will increase.[2]

TRIPLE LF-VFO flowchart


Note for frequency modulation: A high frequency can easily be deeply modulated by a low rate, but a low frequency is much harder to modulate deeply with high frequency. A S&H changes this FM equation into a pure statistic function that becomes pitch independent, resulting in slow rates reacting much deeper to faster rate modulation signals as without the S&H. For example, when a 1Hz LFO is modulated with a 1kHz signal there may only be a tiny bit of 1kHz zippery noise in the LFO signal, but the 1Hz will not seem to change much. But by using a S&H on the 1Hz LFO it will instead go all over the place, defined by the average amplitude of the 1kHz signal.

To use the S&H modulation on LFO C it is often a good idea to not set the LFO C rate knob to its maximum. While there are not set limits for the minimum rate times, a very large negative modulation signal can cause a LFO to stop oscillating. If this happens when the LFO C rate knob is at its minumum, the modulation level knob is fully open, and a sampled negative signal is stopping the LFO, and thus also not sampling a new value that can start it again. In this case LFO C may appear to be frozen. In that case you can just open the rate knob a bit until it starts oscillating again. Or wait for a very long time for the S&H capacitor to eventually loose its charge.[2]

Panel design for a Rob Hordijk TRIPLE LF-VCO

Internal Normalisations

Many of Rob's designs feature internal connections or 'normalisations' between inputs and outputs. These can be broken by inserting jacks into the inputs. When found together in triple-module formation the following normalised connections were made:

  • LF-VCO - C S/H (internal) > LF-VCO A Modulation input
  • LF-VCO - C TRIANGLE output > LF-VCO A Fluctuation input
  • LF-VCO - A SINE output > LF-VCO C Modulation input
  • LF-VCO - B PULSE output > DUAL ENV - GATE IN

This means that when no external signals are applied to the inputs, and their modulation input level knobs are opened, LF-VCO A and LF-VCO C cross-modulate one another.[2]

External Links

References

This page uses Creative Commons Licensed content from Mod Wiggler Wiki:Rob Hordijk Designs (View authors).

  1. ^ a b c d Rob Hordijk
  2. ^ a b c d LF-VCO by Benoit Faivre (2018)

External links

  • Rob Hordijk explains the Triple LF-VCO at the European Electro Music Event 2012, Mallorca, Spain.
Retrieved from "https://sdiy.info/wiki/Rob_Hordijk_Triple_LF-VCO?oldid=20043"