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[[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.
Contact Rob directly for details about his modules: rhordijk@xs4all.nl. <br>
Rob also has a subforum at the Electro-Music forum site:
http://electro-music.com/forum/index.php?f=185


==5U Module Information==
=== 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.<ref name="rh" /> '''LF-VCO A'''<nowiki/>'s frequency modulation input is normalised to '''LF-VCO C's S/H output. '''
<br>
<b>OSC HRM</b><br>
<i>Price 325 euro</i><br>
The Harmonic Oscillator module (OSC HRM) is used to create pitched waveforms with
dynamically controlled timbres. Pitch control law is 1V/Oct and the module uses a platinum
element for temperature stabilization of the pitch curve. Maximum frequency range is from
0.5 Hz to 16.000 Hz and the scale is perfectly tuned in the middle six octaves up to a pitch of
4.000 Hz. When playing pitches higher as 4000 Hz the 1V/Oct scale starts to break down, due
to the necessary internal bandlimiting in the harmonic generators.
The module uses a biquad sine/cosine oscillator at its core and through a process of recursion
harmonic series of overtones are generated. There are two recursion paths, one that produces
all harmonics and one that produces only the odd harmonics. By gradually opening the knobs
that control the amount of recursion more and more harmonics are generated. When only the
all harmonics path is used the waveform morphs smoothly from a sinewave to a waveform
that closely resembles and sounds like a sawtooth or an inverted sawtooth. Opening only the
odd harmonics knob will smoothly morph from a sinewave to a squarewave. When opening
both knobs effects like pulse wave modulation are possible. Building up these harmonic series
is under full voltage control and can be modulated from slow LFO speeds to fast audio rates
to create FM timbres. When the waveforms are modulated there is a negligable amount of
detune (less than 1 cent), though when modulating at audio rates an asymmetry in the
modulating waveform can cause detune effects on deep modulations.
There is an additional VCA incorporated in the module. The final output signal can be taken
from a point just before the VCA and at the output of the VCA. This enables the module to be
easily used in a situation where one wants to modulate another module by an audio rate signal
and have the modulation depth under voltage control using e.g. a LFO waveform, an envelope
voltage signal or a play controller that produces a control voltage, while still having the full
output level signal available on the full output to serve different purposes.
The waveforms have an exceptionally warm sound and when dynamically modulated have a
deep spatial and organic character.
With only one OSC HRM and one DUAL ENV module you can already have a voice with
dynamic timbral and volume control that can do e.g. a pretty solid bass line
<br><br>
[[File:Hordijk_osc_fc.gif]]
<br><br>


=== LF-VCO B ===
<b>Dual Phaser </b><br>
'''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.
<i>Price: 385 euro</i><br>
The internal CV voltage scale is 1V/Oct. Each phaser has a reasonably accurate one volt per octave direct control input that can track the keyboard voltage. Normalization is used, routing the V/Oct input signal of phaser1 into phaser2 when the phaser2 V/Oct input is left unplugged. Total control range is about 18 octaves. The Frq knob goes over the top 9 octaves of this range. Through the V/Oct and Modulation inputs you can go deeper, but you get into the LFO range and audible phasing effects would disappear. It is however possible to use the phasing effect on LFO control signals in the 1Hz to 10Hz range by supplying the V/Oct with e.g. a fixed -5V control signal, which can create quite interesting LFO effects on e.g. drones. All inputs and outputs are DC coupled, so CV signals can pass the module equally well as audio signals. Only the internal resonance is AC coupled, so resonance drops off below roughly 10Hz. Additionally each phaser has a modulation input, also at 1V/Oct when the mode is set to sweep. When the mode is set to spread it behaves like the modulation sensitivity is halved, also when it is in half mode where only half of the poles in each phaser are modulated by this input. These inputs are not normalized, in fact if no plug is connected the modulation level knobs receive a fixed voltage so a manual spread value can be set. Audio input is maximum 12V peak/peak before clipping occurs and there is 6dB attenuation from input to output to enable resonance peaks without clipping. Audio routing is as follows: If a jack is connected to input1, and if input2 is unconnected, then the audio will route into both phasers. In this mode you can use the two phaser outputs as a stereo signal. Connecting a jack to input2 will override this internal input1->input2 connection and separate both phasers. If audio is routed into input1 and if input2 is left unconnected, and if a jack is connected into ónly output2, then the two phasers are automatically set to "inverse parallel" mode. Meaning that if both phasers are set to exactly the same knob settings the phaser outputs would be in exact reverse phase and thus result in almost silence. If audio is routed into input1, and if output1 is connected with a short cable to input2, and if output2 is taken as the overall output, the two phasers are in series and thus result in one 16-pole phaser. To summarize: you can use the phasers fully separated, parallel with two (stereo) outputs on one input signal, parallel with mono output but with one phaser in reversed phase before the mixing of the outputs of the phasers take place on output2, or in series. All this is accomplished by the internal switches in the connectors and only depends on which inputs and outputs have a plug."
<br><br>
[[File:Hordijk_dp.gif]]
<br><br>


'''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. -->
<b>Active Matrix</b><br>
<i>Price: 295 euro</i><br>
The Active Matrix module is a fully buffered eight by eight matrix where any one of eight
input signals can be added to any one of eight outputs. By using ¼-inch tip-ring-sleeve insert
jacks for the matrix nodes (equal to stereo jacks) a whole range of applications become
possible. First the column input signal is buffered and then routed to the tips of the nodes in
that column. The ring signals of the nodes are basically summing inputs and summed to the
final output signals at the ends of the rows. By connecting a stereo jack where the tip and the
ring are connected directly together, a connection with unity gain is made from a column
input to a row output. If the tip-ring connection in the jack goes through a resistor an
additional attenuation can be accomplished. E.g. a 30k resistor will attenuate by 6dB and a
91k resistor by 12dB.
When a stereo audio cable is soldered to a jack plug and on the other side of the cable a
potentiometer is attached the potentiometer will act like a pot on the node, enabling to set the
mix level by the pot. Basically each node is an insert, just like the inserts on a mixing desk.
And can thus be used in the same way. So, using a jack with a pot means to ‘insert’ the pot
into the signal path. This means that you can insert any other outside world device in the
signal path by using an insert cable with a stereo jack on one side and two mono jacks on the
other, provided signal levels match of course (e.g. 5V pp oscillator output signals will
severely overload line level inputs on e.g. a digital effects rack or the guitar input of a
stompbox). One could also connect a resistive sensor like a light dependent resistor (LDR) to
a jack and make the node light sensitive.
Each column also acts like a multiple. When a mono jack is connected into a node it will pick
up the column input signal from the tip. But the ring input is now short circuited to the ground
through the sleeve of the mono jack and will so disable any input from this particular node to
the row output. This will not interfere with any other nodes in the same column or row,
because of the full buffering of both the column inputs and row outputs. So, any node that is
not used to route a signal to a row output can be used as a multiple output. Meaning that the
matrix is also eight multiples with one buffered input and eight buffered outputs on each
multiple.
Matrices with bigger sizes can be built on demand. Input columns come in multiples of eight
and any number of output rows are possible.
<br><br>
[[File:Hordijk_am.gif]]
<br><br>


'''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>
<b>MiniBay</b><br>
* SYNC (up) : '''LF-VCO B''' is synced to '''LF-VCO C''' or to an external signal
<i>Price: 225 euro</i><br>
* MODE (center) : '''LF-VCO B''' is free running
The MiniBay is a smaller version of the Active Matrix. It has a four input by six output fully
* HALT (down) : '''LF-VCO B'''<nowiki/>'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.
buffered matrix plus two passive multiples with five jacks each. The matrix section works
exactly like the 8x8 Active Matrix.
<br><br>
[[File:Hordijk_mb.gif]]
<br><br>


=== LF-VCO C ===
<b>Dual Envelope Generator</b><br>
'''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).
<i>Price: 295 euro</i><br>
The Dual Envelope module (DUAL ENV) is a fully voltage controlled envelope generator
specifically designed to be used with sequenced music. There are two different types of
envelopes available, one is a four stage (attack, decay1, break level, decay2, release) envelope
and the second is a one stage envelope (decay only). Both envelope generators share the same
gate input, meaning that they can not be triggered separately. Triggering treshold is at roughly
100mV above ground and also accepts e.g. triangle waves.
The ADBDR envelope is primarily intended to be used for volume envelopes. When the
decay2 knob on the first envelope generator is fully open the decay2 acts like the sustain that
you find on most of the traditional envelope generators. In this case the break control will act
like the sustain level. There are CV inputs for the attack, decay1, decay2 and release rates.
The CV for the attack is inversed, so increasing the CV level will shorten the attack time
while increasing the decay times for the decay1, decay2 and release. This means that when
e.g. the key velocity voltage is used a higher velocity will shorten the attack and increase the
other decay times. Rate settings can be from really snappy to pretty slow. Care was taken that
you still have good control over the rates when in the snappy range.
The second envelope generator is intended as a modulation envelope generator to e.g. sweep a
filter or control the harmonic waveshaping of an OSC HRM module. It has an extra output
that is controlled by a bipolar mix knob that can invert the envelope shape and also gives
some extra overall ‘sink’ or ‘lift’ when the output level is increased. Rate can be set from a
glitch to about a minute.
When modulating decay times with control voltages it is good advise to keep the voltage fixed
while the envelope is developing. E.g. trying to modulate the decay time with an audio rate
signal does in general not produce sensible results. A S&H is integrated into the module to
sample the decaytime modulation input signal for the second envelope generator on every
new gate trigger. This way the modulation amount will stay fixed until the module is triggered
again by a new gate pulse. The sampled signal is also brought out on a connector, so it can be
routed to a CV input on the first ADBDR envelope generator. Or be used in any other S&H
application.
The ADBDR envelope is designed in a way that is hás to finish its attack phase to reach its
peak level before it can be retriggered. When used for sequencing this allows for complex
envelope shapes that give interesting rhythmic effects, but when used for keyboard play it
might feel a bit strange to play the module with long attack times and fast play.
Note that there are no attenuator knobs to set the amount of modulation for the ADBDR
envelope CV inputs, these inputs are at full sensitivity. They can be connected directly to e.g.
the velocity CV or CC# CV outputs of a MIDItoCV converter, but when modulated from
other sources one might need an extra CV mixer module to set the modulation levels properly
<br><br>
[[File:Hordijk_de_fc.gif]]
<br><br>


[[File:TriLfoSH flowchart.jpg|thumb|TRIPLE LF-VFO flowchart with new Sample and Hold function.]]
<b>Phaser Filter</b><br>

<i>Price: 325 euro</i><br>
=== Sample & Hold Function ===
The Phaser Filter module combines 5 allpass poles with three lowpass poles in one module.
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 five allpass poles are configured as a phaser with positive feedback resonance control,

creating two resonant peaks when opened. Then a crossfade knob fades between the input and
The S/H is triggered every change of direction (rising to falling, or falling to rising)
the output of the phaser and this crossfade mix is the input signal into the lowpass filter. At

the end of the allpass chain before the crossfader is a phaser monitor output. The lowpass
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.
section has a cutoff slope of -18dB/Oct and its own resonance control.

Both the phaser section and the lowpass section have a 1V/Oct control law. The phaser has
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. -->
one modulation input and if it is not connected the audio input signal is used as the

modulation signal. This allows for dynamic waveshaping of the input signal on the time axis

without detuning to signal.

The filter section has two modulation inputs, if the first is not connected the filter audio input
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.
signal is used to modulate the filter cutoff, allowing for even more dynamic waveshaping just

like in the phaser section. If the second modulation input is not used it uses a signal from
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]]
halfway the lowpass poles to self-modulate, thus producing all-harmonic distortion on the
=== Internal Normalisations ===
resonance peak when the resonance is set fairly high.
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:
When the 1V/Oct input jack for the filter is not used it inherits the signal from the phaser

section 1V/Oct input jack.
* LF-VCO - C S/H (internal) > LF-VCO A Modulation input
Both phaser and filter can sweep over a range of roughly 18 octaves and can be modulated up
* LF-VCO - C TRIANGLE output > LF-VCO A Fluctuation input
to really high audio rates. In this last case FM-type and ring-modulator-type effects occur, but
* LF-VCO - A SINE output > LF-VCO C Modulation input
with much more timbral control than traditional ring-modulators. E.g. when the outputs of two
* LF-VCO - B PULSE output > DUAL ENV - GATE IN
OSC HRM modules, set to sinewave output and tuned in some interval, are mixed and routed

into the filter just slight amounts of the internal modulation on either the phaser or the filter
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" />
will start to produce ‘undertones’ and ‘overtones’ that are sum and difference frequencies of
== External Links ==
the interval. This exemplifies the idea behind the Phaser Filter architecture, to not only take

material away like a normal filter does but to also produce new material not present in the
* [https://thehordijkmodular.blogspot.com/search/label/Triple%20LF-VCO TRIPLE LF-VCO] on Benoit Faivre's Hordijk Modular Blog
input signal and combine the both to create a vast range of possible timbres.
* [https://www.youtube.com/watch?v=9qhjG5GJLGc Rob explains the LF-VCO] at the European Electro Music Event (2012)
<br><br>
* [https://www.youtube.com/watch?v=LP-B37O3mKI Rob explains the new S/H function] in his workshop (2018)
[[File:Hordijk_pf_fc.gif]]

<br><br>
== References ==
{{From Mod Wiggler Wiki|Rob Hordijk Designs}}
{{reflist}}

== External links ==
* Rob Hordijk explains the [http://www.youtube.com/watch?v=9qhjG5GJLGc&list=PLAC347DE38ABA9E8D&index=3 Triple LF-VCO] at the European Electro Music Event 2012, Mallorca, Spain.

[[Category:Original Rob Hordijk Design]]
[[Category:5U modules]]

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.
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