Mutable Instruments Shruthi

2 digital oscillators

• band-limited sawtooth with adjustable phase
• band-limited square wave with adjustable pulse-width
• band-limited triangle wave with adjustable waveshapping
• phase-distortion emulation of a low-pass filtered sawtooth (casio CZ-101)
• phase-distortion emulation of a low-pass filtered sawtooth with high resonance (casio CZ-101)
• phase-distortion emulation of a low-pass filtered sawtooth
• mysterious phase-distortion thing (could have been in the CZ-101 if the engineers at casio dared…)
• phase-distortion emulation of a Jew’s harp
• stack of 4 detuned sawtooth waves (with aliasing)
• simplistic FM (1>2 configuration), with adjustable modulation index and frequency ratio
• wavetables, wavetables, wavetables!
  • sweepable table of basic waveforms
  • tampura transwave
  • PPG harsh creature
  • single cycle waveforms taken from D50 patches
  • cello transwave
  • slap bass transwave
  • organ/drawbars single cycle waveforms
  • male voice
  • user wavetable, can be edited by SysEx messages
  • 9 wavetables inspired by the original PPG wave
• harsh, aliasing-full waveforms obtained by bit-toggling
• sine wave with variable amount of bitcrushing
• poor man’s square with pulse-width modulation (plenty of aliasing but fat for basses)
• colored noise (sweep from low-pass filtered white noise -> white noise -> high-pass filtered white noise)
• lo-fi vowel synthesis (think “speak and spell”) with vowel morphing

Mixer

• adjustable oscillator balance
• mixing algorithms: simple sum, simple sum with synchronization, ring modulator, xor modulator, sum with post-mixing tanh fuzz, mixing with sample rate reduction, bit-depth reduction, fold distortion
• extra sources: noise, sub-oscillator (triangle, square, pulse, -1 or -2 octaves) or percussive attack generator (click, glitch, blow, metallic, pop)
• rhythmic control of the mixer, allowing the oscillators / noise source / sub-oscillator to play in turn at each new note, or according to drum-like patterns.
• duophonic 1-oscillator mode (when two keys are held simultaneously, oscillator 1 plays the first note ; oscillator 2 the second)

Audio quality/resolution

• Internal digital audio signal processing chain: 39216 Hz, 8 bits.
• Internal digital control signals processing chain: 980 Hz, 8 bits.
• Digital outputs: 10 MHz, 1 bit.

Filter

• Exchangeable analog signal processing boards:
  • SMR4mkII: 4-pole LPF and linear VCA built with the widely available LM13700 transconductance amplifier and TL074 op-amp
  • Dual SVF: Two 2-pole multimode filters with serial/parallel routing
  • Digital filter: Digital emulation of a 3-pole low-pass / hi-pass + a bunch of lo-fi digital effects (distortion, bit-crushing, delay, comb filter)
  • Polivoks: A clone of the filter of the dark and gnarly Polivoks ; with LP/BP modes ; a switchable distortion, and brutal filter FM feedback
  • 4-Pole Mission: A clean 4-pole based on the high quality SSM2164, from which are derived 15 different filter responses (LP, HP, notch, allpass…) according to a technique popularized on the Oberheim Xpander. Additional circuitry provides 4 different “flavours” of the resonance self-oscillation, from pure and liquid to chaotic and distorted

Modulation

• LFOs: 2, with square, sawtooth, triangle, sample & hold, step sequence, or wavetables shapes. Syncable to tempo. Adjustable “raise/attack” time. LFOs can be free-running, sync’ed to envelope retriggers, or retrigger envelopes.
• envelopes 2 ADSR
• modulation matrix: up to 12 source -> destination connections. Adjustable modulation amount in the -100% — 100% range
• modulation sources:
  • LFO 1/2
  • step sequencer
  • first / second half of the step sequence
  • arpeggiator gate
  • mod. wheel
  • aftertouch
  • pitch bender
  • DC offset
  • CV inputs 1/2/3/4
  • MIDI CC 16 to 19
  • noise generator
  • env 1/2
  • random value resampled at each note on
  • note velocity
  • note number (eg for filter tracking)
  • keyboard gate
  • audio signal from the mixer output (decimated at 1kHz)
• modulation destinations:
  • filter cutoff
  • VCA gain
  • pulse width/Parameter osc. 1/2
  • wide pitch osc. 1/2
  • pitch, applied to osc 1 & 2 simultaneously
  • very fine pitch, applied to osc 1 & 2 simultaneously
  • oscillator balance
  • noise level
  • subosc level
  • resonance
  • PWM CV output 1
  • PWM CV output 2
  • Envelopes attack speed
  • LFO1 FM
  • LFO2 FM
• New modulation sources can be created by combining 2 existing modulation sources with mathematical operations

Performance

Clock/tempo generator

• internal clock: 40-240 BPM, with some additional extra fast tempi for effects (270, 300, 360, 480, 600, 720, 960)
• external MIDI clock with divider
• 6 groove templates (swing, shuffle, push, lag, human, monkey) with adjustable amount

Arpeggiator

• 1-4 octave range
• up, down, up&down;, random
• 15 preset rhythmic patterns + 1 programmable rhythmic pattern
• warp: creates complex rhythms by cyclical repetitions of steps (eg 1212343456567878 instead of 12345678)
• latch/hold

Sequencer

• 16 steps, with legato/slide, velocity, and modulation
• 4 modes corresponding to different interactions between the sequence and keyboard play: latch / transpose / loop recorder / override

Performance

• custom page in which 4 user-selectable parameters can be assigned to the 4 editing pots
• microtunings/key maps for arabic scales (1/4 tones) and a selection of hindustani ragas
• portamento, legato on/off
• master tune

System and memory

• complete MIDI implementation, including patch editing by CC or NRPNs, patch and sequencer data transfer, full memory backup, wavetable transfer.
• MIDI out modes: off, thru, thru+knob movements sent as CC, sequencer/arpeggiator generated events only, polychaining, split (plays notes below split point, forwards the other notes)
• patch memory: 144 patches and 144 sequences stored in EEPROM (no backup battery required). Can be upgraded to 464 / 464.
• firmware update by SysEx

Hardware and connectors

• power: 2.1mm connector, requires 7.5V-9V 300mA supply (can be unregulated). Center pin positive (+), outer collar negative (-)
• audio input/output: 6.35 Jack (Mono audio out), 6.35 Jack (External signal in)
• cv inputs: up to 4 CV inputs for easy experimentation with controllers. Warning: only use a signal in the 0-5V range. Deeper or higher peaks in the signals might damage the Shruthi-1’s ADC.
• cv outputs: up to 2 PWM CV outputs.
• MIDI: in, out
• serial: extra UART TX pin available on control panel board (might be used in future firmware updates to control extension boards)
• ISP connector for firmware development
• controllers:
  • 8 facade LEDs (current page / modulation matrix visualization)
  • 6 navigation switches
  • 4 pots for patch editing
  • clickable rotary encoder for fine parameter adjustment or navigation
  • backlit 2x16 LCD display