Mutable Instruments Anushri User Manual

Mutable Instruments | Anushri - User manual

Congratulations for having successfully built Anushri!

Anushri is a monophonic synthesizer with an all-analog signal path, paired with a lo-fi digital drum
synthesizer. These two sections are controlled by an on-board sequencer/arpeggiator, featuring generative
drum pattern sequencing. Anushri is open to the modular world thanks to its analog patching area.

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Mutable Instruments | Anushri - User manual

A. The upper group of knobs and switches controls the analog sound synthesis. The signal “flows” from

left to right: VCO, mixer, VCF. Most of these knobs are directly interacting with the analog audio signal (no
latency, no stepping… but no MIDI control).

B. The lower group of 10 knobs can serve multiple functions:

Editing the remaining parameters of the synth.
Setting sequencer/arp/MIDI keyboard options.
Controlling the drum synth and drum sequencer.

These 3 different “pages” can be activated by the first column of buttons labelled Synth, Clk/Kbd and

Drums. One of the three LEDs in the vertical column indicates the current page.

Note that if you intend to play Anushri as a synth, without the drum machine and without experimenting
with its sequencer, you can leave it on the Synth page forever and enjoy a “1 knob per function” layout.
Even if you are using the sequencer and drum machine, you’ll notice that you rarely switch pages.

C. Output volume control.

D. Additional CV/Gate/Audio I/O for modular systems.

E. Indicator LEDs. The purpose of the LEDs is shown below:

LFO. The brightness of this LED reflects the LFO value.
Gate. This LED is lit when a key is held or when the gate input is high.
Beat. This LED is lit when the steps 1, 5, 9, 13… of the step sequencer are active.

The 3 remaining LEDs indicate the active page, and thus the function of the lower group of knobs.

F. Switches. The first column of 3 switches is used to select the active page. The second column of 3

switches controls the sequencer. The Hold button serves a few additional functions when held and used
as a “shift” key - this will be revealed throughout this documentation.

G, H. MIDI in and MIDI out.

I, J. Audio out and Audio in. The input signal goes through the VCF and VCA.

K. On/Off switch.

L. Power supply connector. A 7.5V or 9V DC supply must be used, with a current rating above 200mA.

The connector has a 2.1mm barrel, with a positive center tip polarity. Most universal power supplies allow
the polarity to be selected — the polarity being often represented by a diagram like this: – (o , or by the
indication tip:. Anushri’s power supply circuitry has a reverse polarity protection and can handle voltages

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Mutable Instruments | Anushri - User manual

up to 12V. Above this, one of the chip inside the unit could be destroyed by overvoltage.

This section documents Anushri’s analog synthesis section.

Anushri follows the classic subtractive synthesis scheme: a VCO producing a rich waveform is
filtered/colored by a VCF, and the level of the resulting sound is controlled by a VCA. One particularity of
Anushri is that it also includes an additional digital square wave generator. Even if this terminology is
inaccurate, it’ll be referred to as the DCO in the rest of the documentation (For the sake of accuracy: the
square wave comes from a programmable interval timer on the main MCU). This second source can be
used to achieve sounds traditionally reserved to dual oscillator synthesizers, such as FM, hard-sync, or
rich detuned sounds.

Anushri has 3 envelope generators: an AD envelope used for VCO and PWM control; an ADSR1 envelope
used for VCF control; and an ADSR2 envelope used for VCA control. However, the user interface does
not allow individual editing of these envelopes: the AD and ADSR1 envelope share the same attack and
decay settings; and ADSR2 is controlled through a morphing parameter which gives it the shape of

ADSR1, or an increasingly rigid shape resembling a Gate signal.

Anushri has 2 LFOs: a main LFO, syncable to tempo, with 8 different waveforms; and a vibrato/growl
triangle LFO, the amplitude of which is controlled by the modulation wheel.

All the synthesis parameters can be accessed from the front panel by pressing the Synth button.

FM controls by which amount the DCO signal modulates the frequency of the VCO. This modulation is

linear FM. Dissonant and metallic timbres can be achieved by setting FM to a high value, and by detuning
the DCO and VCO with the VCO range or VCO detune knobs.

VCO mod controls which modulation is applied to the VCO. In central position (the potentiometer has a

detent at 12 o’clock), no modulation is applied to the VCO. When turning the knob clockwise, an
increasing amount of LFO modulation is applied. When turning the knob counter-clockwise, an increasing
amount of AD envelope modulation is applied.

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Mutable Instruments | Anushri - User manual

PW adjusts the pulse-width of the square waveform. In central position (the potentiometer has a detent at

12 o’clock), the output signal is a square waveform.

PW mod controls the modulation applied to pulse-width. In central position (the potentiometer has a

detent at 12 o’clock), no modulation is applied to the pulse width. When turning the knob clockwise, an
increasing amount of LFO modulation is applied. When turning the knob counter-clockwise, an increasing
amount of AD envelope modulation is applied.

Sync resets the cycle of the VCO every time the DCO completes a full cycle. This works particularly well

when the VCO is set to a higher pitch than the DCO (high value of the VCO range pot), and when an
envelope or LFO modulation is applied to the VCO, for this ewwwwww sound. Note that when the VCO
has a lower pitch than the DCO, no sound can be heard. This is a useful trick if you want to disable the
VCO for external signal processing!

Glide adjusts the portamento time between consecutive notes. This causes the pitch of the previous note

to slowly slide towards the pitch of the next note.

VCO range adjusts the pitch of the VCO relatively to the note played on the keyboard, from -12 semitones

to +36 semitones. This potentiometer is deliberately “steppy”, with one step for each semitones, and a
dead-band at octaves (-12, 0, 12, 24, 36 semitones).

VCO detune adjusts the VCO pitch on a fine scale, to create a slight detuning effect between the VCO

and the DCO.

Mix controls the balance of the sawtooth and square waveshapers. In center position, both waveshapes

are mixed together. Fully turned clock-wise, only the square wave can be heard. Fully turned counter­clock-wise, only the sawtooth wave can be heard.

Sub level controls the level of an additional signal added to the mix. This signal is selected with the Sub

switch, from one of these 3 sources:

The DCO.
A square sub-oscillator running one octave below the VCO.
A square sub-oscillator running two octaves below the VCO.

Note that any pitch modulation applied to the VCO will also be applied to the sub-oscillator; but due to the
way the sub-oscillator synchronizes its pitch to the VCO, interesting sync-like or quantization/arpeggiation
effects can be heard.

Anushri’s filter is a 2-pole multimode filter based on the State-Variable topology - a circuit made famous in
the synth world by the Oberheim SEM. The filter can self-oscillates smoothly when resonance is set to
high values.

Cutoff adjusts the filter cutoff frequency, from 18 Hz to 22kHz. Note that by default, filter cutoff frequency

tracks the note played by the keyboard (this can be disabled by sending a specific CC message to
Anushri).

Resonance adjusts the filter resonance, progressively emphasizing the frequencies in the vicinity of the

cutoff frequency.

VCF env mod controls the amount of ADSR1 modulation applied to filter cutoff.

VCF LFO mod controls the amount of LFO modulation applied to filter cutoff.

VCF mode selects the filter mode: low-pass, band-pass, or high-pass.

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The audio input at the back of Anushri (6.35 jack) is routed to the filter input, allowing external signals to
be processed through the filter, fuzz and VCA.

The signal produced by the VCF can be sent to a fuzz circuit before getting into the VCA. Switch the Fuzz
control on for a nasty overdriven sound.

LFO shape selects the waveform of the main LFO. The following shapes are available:

Triangle.
Square.
Ramp up.
Ramp down.
Sample and hold. The LFO periodically takes a random value.
Bernouilli process. The LFO randomly switches between a high and low value. The rate of transition is

affected by the rate parameter.
Smooth random process. A continuous random waveform made of lines with a randomly selected slope is

generated. The higher the rate, the higher the digital manic pixie dream cat tweaks the knobs.
Noise. The LFO output is a white noise signal. In this case, the rate parameter of the LFO has no effect.

LFO rate adjusts the speed of the LFO. The LFO frequency ranges from 0.06 Hz (a full cycle takes 16s) to

100 Hz. Note that when the rate setting is set to its minimum value, the LFO locks itself to the
sequencer/arpeggiator clock, so that the LFO accomplishes a full cycle over a period of 4 beats. This
synchronization is achieved through a PLL - it might take a few beats before the LFO effectively locks to
the sequence.

Attack and Decay adjust the envelopes attack and decay time. These settings affect both the AD

envelope (VCO and PWM modulation) and the VCF ADSR envelope. They might affect the VCA ADSR

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envelope too.

Sustain and Release adjust the envelopes sustain level and release time. These settings affect the VCF

ADSR envelope, and might affect the VCA ADSR envelope too.

VCA env controls the shape of the VCA envelope. When this setting is set to 0, the VCA envelope is the

same as the VCF envelope - exactly matching the A, D, S, R settings dialed on the four knobs. When this
knob is set to a middle position, the VCA envelope has a null attack, a 75% sustain, and half the decay
and release times dialed on the Decay and Release knobs. Finally, when this knob is set to the maximum
value, the VCA envelope gets turned into a “gate” signal, with no attack, no decay and release, and a
sustain at full level. Inbetween, some “morphing” between the shapes is applied. Refer to the following
illustration:

One can think of this setting as a “VCA envelope solidity” parameter. Note that when this control is set to
the most extreme “gate” setting, the envelope actually has a non-null but tiny release time (exaggerated
on the drawing). This prevents clicks when a note is released.

Technical note: the LFOs and Envelopes are digitally generated, using a 2.45kHz refresh rate and a 12-bit
resolution DAC (with 16-bit internal computations).

Anushri’s saw-core VCO uses a temperature compensation scheme (published by Osamu Hoshuyama)
which makes it quite stable once the inside temperature of the case has plateaued. A reset-time
compensation scheme (De Franco resistor) attenuates the flat detuning in the higher octaves, allowing the
VCO to track well over the 55 .. 1760 Hz range.

However, to reach these performances, the VCO needs calibration through a set of two trimmers (Offset
and V/Oct) at the back of the board.

To spare you this lengthy process, a software compensation can be enabled that will instantly bias
Anushri’s internal CV conversion stage to reach the right tuning. To enable this correction:

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