Rob Hordijk OSC HRM: Difference between revisions

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Line 1: [[File:Hordijk osc.png\|thumb\|200px\|Panel design for a Rob Hordijk OSC HRM]]The '''OSC HRM''' (Harmonic Oscillator) is a 5U format module designed by [[Rob Hordijk Design\|Rob Hordijk]]. It features controls to adjust frequency, smoothly blend between a range of waveforms, adjust modulation, and includes a built in [[Voltage controlled amplifier\|VCA]]. [[File:Hordijk osc.png\|thumb\|right\|200px]]The 2U wide '''Rob Hordijk 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.<ref name="rh">Rob Hordijk</ref>▼ === Tuning === [[File:Hordijk osc fc.png\|thumb\|right\|200px\|The OSC HRM flowchart.]]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.<ref name="rh" /> ▲~~[[File:Hordijk osc.png\|thumb\|right\|200px]]~~The ~~2U wide '''Rob Hordijk Harmonic Oscillator''' module ('''~~OSC HRM~~''') is used to create pitched waveforms with~~ ~~dynamically~~can ~~controlled timbres. Pitch control law is~~track 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 ~~16000 Hz and the scale is perfectly tuned in the middle six octaves up to a pitch of ~~4.000 ~~4000 Hz. With external CV the pitch range is 18 octaves.<ref>[https://thehordijkmodular.blogspot.com/2018/02/the-harmonic-oscillator-oschrm-lets.html The Harmonic Oscillator (OSC HRM)] by Benoit Faivre (2018)</ref> When playing pitches higher asthan 4000~~ ~~ Hz the 1V/Oct scale starts to break down, due to the necessary internal ~~bandlimiting~~band-limiting in the harmonic generators.<ref name="rh">Rob Hordijk</ref> Later versions feature a toggle switch allowing selection between manual tuning (up), a stable preset frequency (centre), and -1 octave (down). The module also features a CHAIN OUT function that simply passes or [[Mult\|mults]] the 1V-OCT IN signal for use chaining multiple oscillators together. 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.<ref name="rh" /> === Harmonics === 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.<ref name="rh" /> [[File:Hordijk osc fc.png\|thumb\|right\|200px\|The OSC HRM flowchart.]]While an intuitive understanding of the modules functions might suggest a mixer or blend between odd and even harmonics, the results are actually produced by a kind of linear frequency modulation (FM). FM is normally done with two sine waves (such as the Yamaha DX series) but the OSC HRM uses a bi-quad sine/cosine oscillator at its core and through recursion or feedback a harmonic series of overtones are generated. There are two feedback paths using Chebyshev function, one that produces all harmonics and one that produces only odd harmonics. By gradually opening the knobs that control the amount of feedback more and more harmonics are generated. When only the all harmonics path is used the waveform output 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 negligible amount of de-tuneing (less than 1 cent), though when modulating at audio rates an asymmetry in the modulating waveform can cause stronger de-tuning.<ref name="rh" /> === VCA === The OSC HRM also includes a built in VCA. The final output signal can be taken from a point just before the VCA (FULL OUT) as well as the output of the VCA, allowing for parallel processing of modulated and un-modulated amplitude. == References == Line 12 ⟶ 25: == External links == * Rob Hordijk explains the [http://www.youtube.com/watch?v=J3paMIPzg-Q&list=PLAC347DE38ABA9E8D&index=1 OSC HRM] at the European Electro Music Event (2012,) Mallorca, Spain. * [https://vimeo.com/236208519 Rob explains the OSC HRM] at NOVARS (2017) * [https://~~www.gearslutz~~gearspace.com/board/~~electronic~~modular-~~music~~mania-~~instruments~~all-~~electronic~~things-~~music~~eurorack-~~production~~and-modular-synths-effects/588172-hordijk-harmonic-oscillator-sound-clips.html Hordijk Harmonic Oscillator ~~sound~~Sound ~~clips~~Clips] on GearSpace.com * [https://thehordijkmodular.blogspot.com/search/label/OscHRM OSC HRM] on the Hordijk Modular Blog by Benoit Faivre [[Category:Original Rob Hordijk Design]]