Evolver Architecture Overview

Dave Smith Instruments

Dave Smith Mono Evolver Keyboard

Identity

Manufacturer: Dave Smith Instruments (now Sequential)
Type: Monophonic analog/digital hybrid synthesizer
Keyboard: 3-octave (37 keys) with velocity and aftertouch
Programs: 512 (4 banks x 128)
Year: ~2005-2010
OS: Version 1.3+

What Makes It Special

The Evolver is a true stereo synthesizer with parallel left/right signal paths. It combines:

2 analog oscillators (warm, fat, modern CEM-style)
2 digital oscillators (Prophet-VS waveshapes, 128 waves including user-loadable)
2 independent analog lowpass filters (one per channel)
Digital highpass filter
3 ADSR envelopes
4 LFOs
4-track 16-step sequencer
Stereo digital delay
Tuned feedback
Distortion, output hack
External audio processing

The analog/digital hybrid architecture is its superpower -- you get warmth from the analog path and complexity from the digital, with the DSP handling modulation calculations at high precision.

The Evolver voice is built around a high-speed Digital Signal Processor (DSP) that surrounds the analog electronics. The DSP computes control voltages for the analog circuitry with high precision, and also provides the digital audio functions.

Analog components (per channel):

1 analog waveshape oscillator (saw, triangle, saw-tri mix, pulse with variable width)
1 resonant lowpass filter (switchable 2-pole/4-pole, self-oscillating in 4-pole mode)
1 VCA (voltage controlled amplifier)

Digital components (shared/stereo):

2 digital oscillators (Prophet-VS waveshapes 1-128, including 32 user-loadable)
FM synthesis between digital oscillators (bidirectional)
Ring modulation between digital oscillators (bidirectional)
Highpass filter (4-pole digital, pre/post switchable)
Distortion with noise gate (pre/post switchable)
3-tap digital delay (up to 1 second, 16-bit 48kHz, tempo-syncable)
Tuned feedback via two delay lines (one per channel)
Output hack (bit-crushing effect)
All modulation calculations (envelopes, LFOs, routing)

Converters: Two sets of stereo A/D and D/A converters running at 48kHz sampling rate with 24 bits of precision bridge the analog and digital sections.

Stereo Signal Path

The stereo architecture is fundamental to the Evolver's character:

Left channel: Analog Osc 1 + Digital Osc 3 + Noise + External In L --> Analog LPF L --> VCA L
Right channel: Analog Osc 2 + Digital Osc 4 + Noise + External In R --> Analog LPF R --> VCA R
Post-VCA (digital, stereo): HPF --> Distortion --> Pan --> Delay --> Tuned Feedback --> Output

The two analog lowpass filters are normally driven together in tandem but can be separated using the Split parameter or independent filter modulation destinations. Since they are true analog, there are always subtle differences between the two, giving a natural stereo character.

Modulation Architecture

The Evolver provides extensive modulation capabilities:

3 ADSR envelopes: ENV 1 (dedicated to filter), ENV 2 (dedicated to VCA), ENV 3 (freely assignable with delay parameter)
4 LFOs: Each with shape (tri, rev saw, saw, square, random), frequency (0-150 or tempo-synced), amount, destination, and key sync
4 modulation slots: Any source --> amount --> any destination routing
4-track 16-step sequencer: Each track can target any modulation destination
MIDI controllers: Velocity, aftertouch/pressure, mod wheel, breath, foot controller -- each with assignable destination and amount
External input analysis: Envelope follower and peak hold for sidechain-style modulation

Modulation destinations include nearly every synthesis parameter (oscillator frequency, level, shape/PW, filter cutoff, resonance, envelope times, delay parameters, feedback, etc.) plus sequencer-only MIDI destinations for controlling external gear.

Filter Topology

The analog lowpass filters are the heart of the Evolver's sound shaping:

2-pole mode: -12dB/octave slope, gentler rolloff, does not self-oscillate
4-pole mode: -24dB/octave slope, steeper rolloff, self-oscillates at high resonance
Frequency range: 0-164 (over 13 octaves) with special smoothing for clean manual sweeps
Envelope amount: Bipolar (-99 to +99) for inverted envelope control
Audio modulation: Analog oscillator modulates its own channel's filter (Osc 1 --> LPF L, Osc 2 --> LPF R)
Key tracking: 0-100 (72 = 1 semitone per note for pitch tracking)
Split: Separates L/R filter cutoffs (raises left, lowers right)

The digital highpass filter (4-pole) can be positioned pre or post the analog filter chain, dramatically changing its role in the signal path.

Program Organization (Factory)

Bank	Programs	Content
1	1-128	Classic keyboard sounds
2	1-128	Classic keyboard sounds
3	1-128	Sequencer-based (use Start/Stop, not keyboard)
4	1-19	Drones (always playing)
4	20-29	Guitar signal processing
4	30-39	Stereo signal processing
4	40-127	Misc keyboard sounds
Any	128	Basic init patch (good starting point)

Controls

Knobs: 58 total (43 pots + 15 encoders)
Pot modes: Relative, Passthru, Jump
LCD: 2x16 character display
Navigation: PARAM 1 (value/program), PARAM 2 (value/bank), +/YES, -/NO
Dedicated switches: Osc 1-4 select, Delay 1-3 select, 4-pole, Sync, Compare, Write
Sequence LEDs: 16 step indicators (double as VU meter in input gain mode)

Key Capabilities for Learning

Subtractive synthesis -- analog oscillators --> analog filters (the classic)
Digital waveshape synthesis -- 128 waveshapes from Prophet-VS lineage
FM synthesis -- digital oscillators can FM each other (bidirectional)
Ring modulation -- digital oscillators can ring mod each other (bidirectional)
Hard sync -- Osc 2 syncs Osc 1
Karplus-Strong -- physical modeling via tuned feedback + noise
Step sequencing -- 4 tracks, 16 steps, any parameter as destination
External processing -- use as a stereo effects unit with envelope follower
Poly chaining -- link with other Evolvers/Poly Evolvers for polyphony

Signal Flow

Evolver Signal Flow

Signal Flow Diagram (Mermaid)

Audio Path (Text Diagram)

                    +---------------+
                    |  EXTERNAL     |
                    |   INPUTS      |
                    |  (L + R)      |
                    +-------+-------+
                            |
              +-------------+-------------+
              |                           |
              v                           v
    +--- LEFT CHANNEL ---+    +-- RIGHT CHANNEL --+
    |                     |    |                    |
    |  Analog Osc 1       |    |  Analog Osc 2      |
    |  Digital Osc 3      |    |  Digital Osc 4      |
    |  Noise              |    |  Noise              |
    |  External In L      |    |  External In R      |
    |         |           |    |         |           |
    |         v           |    |         v           |
    |  +-----------+      |    |  +-----------+      |
    |  | ANALOG LPF|      |    |  | ANALOG LPF|      |
    |  | (2/4 pole) |      |    |  | (2/4 pole) |      |
    |  | +resonance |      |    |  | +resonance |      |
    |  +-----+-----+      |    |  +-----+-----+      |
    |        |             |    |        |             |
    |        v             |    |        v             |
    |  +-----------+       |    |  +-----------+       |
    |  |    VCA    |       |    |  |    VCA    |       |
    |  +-----+-----+       |    |  +-----+-----+       |
    |        |             |    |        |             |
    +--------+-------------+    +--------+-------------+
             |                           |
             +-----------+---------------+
                         |
                  +------v------+
                  |  HIGHPASS   |
                  |  FILTER    |
                  |  (digital)  |
                  +------+------+
                         |
                  +------v------+
                  | DISTORTION  |
                  | (+ noise    |
                  |   gate)     |
                  +------+------+
                         |
                  +------v------+
                  |   OUTPUT    |
                  |    HACK    |
                  +------+------+
                         |
                  +------v------+
                  |    PAN     |
                  +------+------+
                         |
             +-----------+----------+
             |                      |
             v                      v
       +----------+          +----------+
       |  DELAY   |          | TUNED    |
       | (3 taps, |<--FB1--> | FEEDBACK |
       |  1 sec)  |          | (L + R   |
       +----+-----+          |  delay   |
            |                |  lines)  |
            |      FB2       +----+-----+
            +--- (to filter) ---->|
            |                     | (feeds back to filter input)
            v                     v
      +----------+          +----------+
      |  STEREO  |<-------->|  STEREO  |
      |  OUTPUT  |          |  OUTPUT  |
      +----------+          +----------+

Pre/Post Routing Options

Both Distortion and Highpass Filter can be switched between two positions in the signal chain. This dramatically changes their sonic role:

Component	Pre (After ExtIn)	Post (After VCA)
Highpass	Before analog LPF, only affects external input	After VCA, before delay -- filters everything
Distortion	Before analog LPF, only affects external input	After VCA+HPF, before delay -- distorts everything

Source: DSI Manual p.26

Oscillator Routing (Fixed)

The oscillator-to-channel assignments are hardwired:

Component	Channel	Notes
Analog Osc 1	Left	Saw, Triangle, Saw-Tri, Pulse (variable width)
Analog Osc 2	Right	Saw, Triangle, Saw-Tri, Pulse (variable width)
Digital Osc 3	Left	128 waveshapes (Prophet-VS lineage), FM from Osc 4, Ring Mod from Osc 4
Digital Osc 4	Right	128 waveshapes, FM from Osc 3, Ring Mod from Osc 3
Noise	Both	Single noise source mixed equally into both L and R filter inputs
External In	L/R or Mono	Configurable: Stereo, Mono Left, Mono Right, L Control + R Audio

Source: DSI Manual p.7-8, p.15-16

Modulation Sources

Source	Notes
ENV 1	Filter envelope (dedicated to LPF cutoff)
ENV 2	VCA envelope (dedicated to amplitude)
ENV 3	Mod envelope (freely assignable, has delay parameter)
LFO 1-4	Each with: shape, freq, amount, destination, key sync
Sequencer 1-4	16 steps each, any parameter destination
Mod Slots 1-4	Source --> Amount --> Destination routing (unfiltered, fast response)
Velocity	Per-envelope velocity sensitivity + assignable destination
Aftertouch/Pressure	Amount --> destination (filtered/smoothed via Misc Params)
Mod Wheel	Amount --> destination (filtered/smoothed via Misc Params)
Breath	Amount --> destination
Foot Controller	Amount --> destination
Pitch Bend	+/- range in semitones (0-12)
Envelope Follower	Tracks left external input level -- useful for sidechain effects
Peak Hold	Detects left external input peaks -- useful for triggering

Source: DSI Manual p.21-23, p.33-35

Key Signal Flow Insights

Stereo is fundamental -- L/R paths are independent through the analog section. Use Output Pan and Filter Split to exploit this.
Feedback creates new timbres -- The tuned feedback loop can act as a physical model (Karplus-Strong) or add resonant character. Frequency range is C0-C4 (4 octaves).
Delay FB2 --> Filter -- This secondary feedback path routes delay output back to the analog filter input, enabling extreme effects and complex resonant structures.
Pre/Post switching -- Distortion and HPF positioning dramatically changes character. Pre = only external input affected; Post = entire signal chain affected.
Noise feeds both channels -- Single noise source, mixed equally into L and R filter inputs.
Audio mod is per-channel -- Osc 1 modulates LPF L, Osc 2 modulates LPF R. This preserves the stereo character even during audio-rate modulation.
Digital oscillators cross-modulate -- FM and Ring Mod are bidirectional between Osc 3 and Osc 4, and both can be active simultaneously for wild results.

Source: DSI Manual p.7-8, Anu Kirk Guide overview section

References

Basic Patch Reference Troubleshooting Guide

37 sessions

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