Instruo I-o47 User manual
I-ō47
Multimode Resonator / Filter
User Manual
3
Description
I-ō47 Multimode Resonator/Filter is a modern take on a vintage
circuit design inspired by the classic synthesisers from the early 1970s.
Unlike many multimode filters, I-ō47 has a steep -18dB/oct slope with
interpolating inputs and tameable resonance.
Although inspired by the past, this module was designed with new
ideas, new features, and most importantly - new quirks. A hybrid design
of matched transistor pairs and precision op-amps was used to create
the circuit’s semi-discrete VCAs, making the I-ō47 a beast of its
own variety.
With on-board limiter/waveshaper, exponential frequency modulation,
pingable resonance, inverted input, and crossfading and mixing
capabilities, I-ō47 fits in every patch.
Features
• Simultaneous low pass, high pass, band pass, and notch filter types
• Self-oscillating resonance with feedback toggle
• 1V/Oct tracking
• Strike input for pingable resonance
• Notch offset with CV control
• Limiter/waveshaper
• Inverting input
4
Installation
1. Confirm that the Eurorack synthesizer system is powered off.
2. Locate 4 HP of space in your Eurorack synthesizer case.
3. Connect the 10 pin side of the IDC power cable to the 2x5 pin
header on the back of the module, confirming that the red stripe on
the power cable is connected to -12V.
4. Connect the 16 pin side of the IDC power cable to the 2x8 pin
header on your Eurorack power supply, confirming that the red
stripe on the power cable is connected to -12V.
5. Mount the Instruō I-ō47 in your Eurorack synthesizer case.
6. Power your Eurorack synthesizer system on.
Note:
This module has reverse polarity protection.
Inverted installation of the power cable will not damage the module.
Specifications
• Width: 14 HP
• Depth: 27mm
• +12V: 50mA
• -12V: 50mA
5
GAIN
IN
Q
COARSE
FINE
1V/OCT
MULTIMODE RESONATOR/FILTER
LIM
FM
LP
BP
HP
CV
N
fc
+–
47
–
fc
1
1/2
1/4
2
4
I-ō47 |öK-əU-'fɔ:ti-'sEv(ə)n | noun (signal processing) the in’s and
out’s of a classic multimode filter/resonator
Key
1. Input
2. Limiter Toggle
3. Gain
4. Inverting Input
5. Low Pass Output
6. Band Pass Output
7. High Pass Output
8. Notch Output
9. Course
10. Fine
11 . FM Input
12. FM Attenuverter
13. 1V/Oct Input
14. Notch
15. Notch CV Input
16. Q
17. Q CV Input
18. Feedback Toggle
19. Strike Input
5
1
4
6
7
8
9
10
11
12
13
14
15
16
17
2
3
1819
6
Input & Output
Input: Audio input of the filter.
• The signal present at the Input will output from all filter types
simultaneously.
Limiter Toggle: The Limiter Toggle sets a fixed level tanh[3] circuit.
Limiting is only applied to the signal present at the Input.
• When the toggle is in the up position, limiting/waveshaping
is bypassed.
• When the toggle is in the down position, limiting/waveshaping
is enabled.
Gain: The Gain fader affects the signal present at the Input.
• If the fader is in the up position, the signal present at the Input will be
at its full scale amplitude.
• If the fader is in the down position, the signal present at the Input will
be fully attenuated.
• If limiting is enabled, the centre position of the Gain fader is
optimised as a “sweet spot” for versatile general purpose use.
Inverting Input: Inverting audio input of the filter.
• The signal present at the Inverting Input is inverted and will output
from all filter types simultaneously.
• The level of the signal present at the Inverting Input is inversely
proportional to the level of the Qparameter. As resonance
increases, the signal present at the Inverting Input decreases.
• This functionality can be used for dynamic signal blending.
Low Pass Output: Low pass filter output.
• Any harmonics above the cutoff frequency are attenuated.
7
Band Pass Output: Band pass filter output.
• Any harmonics above or below the centre frequency are attenuated.
High Pass Output: High pass filter output.
• Any harmonics below the cutoff frequency are attenuated.
Notch Output: Notch filter output.
• This is also known as a Band Stop Filter or a Band Rejection Filter.
• Any harmonics within the stop band are attenuated.
8
Frequency Modulation
Coarse: The Coarse knob controls the cutoff frequency of the low pass
and high pass filters and the centre frequency of the band pass and
notch filters.
• The cutoff frequency is the point at which the filtered signal is
reduced by 3dB in amplitude.
• The centre frequency is the midpoint between the cutoff frequencies
set by the low pass and high pass filters.
• Turning the knob clockwise will increase the cutoff/
centre frequency.
• Turning the knob anticlockwise will decrease the cutoff/
centre frequency.
• If I-ō47 is used as an oscillator, the knob controls the fundamental
frequency of the oscillator.
• Range: ~16Hz - 16KHz.
Fine: The Fine knob is used for minute control of the cutoff frequency
of the low pass and high pass filters and the centre frequency of the
band pass and notch filters. Fine tuning is relative to the value set by the
Coarse knob.
• Turning the knob clockwise will increase the cutoff frequency.
• Turning the knob anticlockwise will decrease the cutoff frequency.
• If I-ō47 is used as an oscillator, the knob controls the fundamental
frequency of the oscillator.
FM Input: The FM Input is a bipolar control voltage input for the cutoff/
centre frequency and applies exponential frequency modulation.
• Control voltage is scaled by the FM Attenuverter and sums with the
level set by the Coarse and Fine knobs.
• If I-ō47 is self-oscillating, the FM Input can be used for exponential
frequency modulation of the generated sine waveform.
9
FM Attenuverter: The FM Attenuverter determines the depth of
frequency modulation applied to the cutoff/centre frequency.
• Turning the knob clockwise will increase the depth of exponential
frequency modulation.
• Turning the knob anticlockwise will increase the depth of
exponential frequency modulation with inverted polarity.
• Centring the knob will attenuate the control voltage signal.
1V/Oct Input: The 1V/Oct Input is a bipolar control voltage input for
the cutoff/centre frequency.
• This is a dedicated exponential frequency control input which
can be used for precise frequency modulation such as ‘keyboard
tracking’.
• If I-ō47 is self-oscillating, the 1V/Oct Input can be used for
consistent pitch tracking of the sine waveform, effectively making
I-ō47 a quadrature sine waveform oscillator.
• Control voltage is summed with the level set by the Coarse and
Fine knobs.
Notch: The Notch knob controls the centre frequency offset of the notch
response output. This parameter affects the Notch Output only.
The numbers surrounding the Notch knob depict a multiplier indicating
an approximate octave offset from the centre frequency.
• ¼ = 0.25 x centre frequency (-2 octave offset). [towards high
pass response]
• ½ = 0.5 x centre frequency (-1 octave offset). [towards high
pass response]
• 1 = centre frequency (0 octave offset). When the knob is set to 1, the
Notch Output is a traditional symmetrical notch filter.
• 2 = 2 x centre frequency (+1 octaves offset). [towards low
pass response]
• 4 = 4 x centre frequency (+2 octave offset). [towards low
pass response]
10
• At the outer extremities of the Notch knob the Notch Output will
duplicate the Low Pass Output (anti-clockwise) or the High Pass
Output (clockwise).
Notch CV Input: The Notch CV Input is a bipolar control voltage input
for the Notch parameter. Signal present at the Notch CV Input will
affect the Notch Output only.
• Control voltage is summed with the knob position.
• Input range: 0V - 5V
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