ASVF-212 Analog State-Variable Filter

A State-Variable Filter is an active filter that uses multiple feedback techniques to produce filter responses (LowPass, BandPass and HighPass) from a single filter with user selection.
Classical SVF filters include controls for Filter Frequency, Filter Q and Gain.
With the ASVF-212, we included deep LFO control for the device’s parameters. A variety of textures and horizons of modulation morphing can be created by routing destinations such as Filter Freq, Filter Q, Low-High Filter Response, and Notch-Peak FIlter Response.
The ASVF-212 has an additional Notch Filter (Band Stop filter) and Peak Filter (BandPass filter).
The device can also take advantage of Envelope Follower tricks with modulation destinations for FIlter Freq, Filter Q, Low-High Filter Response, and Notch-Peak Filter Response with a few Envelope Follower detection modes.
Envelope Follower can work with main incoming signal or additional external input.

What makes the ASVF-212 different from a typical SVF filter? It is a Stereo filter-bank (LP, HP, BP, Notch, Peak filters) with deep LFO and Env. Follower modulation.

The ASVF-212 includes a Blend knob (Dry/Wet mixture of incoming and processed signals) to create more interesting and creative effects. The user can use the included hard clipped Limiter to control the final signal by adjusting the necessary Gain and Pre-Gain (unprocessed) levels. Drive works as overdrive and compressor effect.

Filter at higher Filter Q values have small oscillation. In version 2.0 now is possible to activate Filter Self-Oscillation with filter keytracking, which allows you to use the filter as Oscillator controllable by midi keys.

The ASVF-212 is a modern stereo SVF filter with advanced features and classical analog SVF possibilities. It allows for a lot of variations of active filtering, resulting in a unique sound.

ASVF-212 Device scheme

ASVF-212 is a State Variable filter, that makes an excellent notch filter by summing the high and low pass outputs with band pass. It is easily tuned, and the Q is adjustable so the width of the notch can be varied. This is one of the most versatile and flexible filter types.

Notch VS Peak filters

A Notch filter is basically the opposite of a BandPass filter, it rejects, or stops, a specific band of frequencies. A Notch filter is also known as a “Band Stop Filter”. It works as summing of HighPass and LowPass output responses.

A Peak filter is a frequency filter that passes a narrow band of frequencies and stops all other frequencies. This is a very narrow bandPass filter and the opposite of a Notch filter. For example, peak filters are used in WahWah effects.

Main SVF Parameters

Filter Frequency - Cuftoff Frequency of HighPass, BandPass and LowPass filters

Filter Note Key - Basic Note Keys steps identical to Hz values of Cutoff Freq for filter & Osc keytracking

Frequency Mode - Set filter mode between the classic Frequency value and key note value. At the Note mode, avaliable to use Filter & Self-Oscillation keytracking (fx can be used as oscillator)

Filter Q - Strength of resonant peak at cutoff frequency

Low-High Freq Response - Fade between LowPass and HighPass response

Notch-Peak Freq Response - Fade between Notch/BandStop and Peak/BandPass response

Filter Smoothing - Filter speed (in seconds) that makes sound of the filter smoother with higher level

LFO

Wave - LFO Waveforms: Sqr, Sine, Tri, Saw, Uniform, FlatMid, EarlyComb, Essence

Destination - LFO destination: Filter Freq, Filter Q, Low/High Filter Response, Notch/Peak Filter Response

Modulation Way - Increase / Reduce the destination mod parameter

Mod Index - Ramping LFO steps. 0% switches from one value to the next

Rate - LFO Rate (mode in sync with Step grid or Time in seconds)

Random Amt - Scale each step of LFO by a random amount

Sync Mode - Set the LFO rate in steps per beat or steps per second

LFO Amt - Amount of the LFO modulation

Retrigger - Restart LFO steps after pauses (sync = Sec), and when Bar beat changed (sync = Beats)

Rate Affect - How much the value affects the LFO Rate

Drift Contour - How much the value affects the LFO Wave. Change the waveform from hard to soft curve.

Envelope Follower

Mode - Envelope detection modes:
LIN: Linear voltage measurement up to the threshold level;
LOG: Logarithmic dB measurement above the threshold level;
GATE: Switch off and on as the signal level passes the threshold

Threshold
LIN: Audio level for full modulation;
LOG: Audio level for no modulation;
GATE: switching Threshold.
Attack - Rise time when the audio level increases, or the gate opens

Release - Fall time when the audio level decreases, or the gate closes

Destination - Off, Filter Frequency, Filter Q, Low/High and Notch/Peak frequency response

Env. Amount - Amount of the Envelope Filter modulation to the selected destination

Env. Source:
- INTERNAL: use main incoming signal processed by ASVF-212
- EXTERNAL: use external incoming signal from EXTERNAL ENV. FOLLOWER Inputs

Limiter & Drive

Clip Limiter - Limiter on/off. CPU safety hard clipping limiter
Release - Recovery time
Drive On/Off - Drive On/Off button. Drive can work only if as part of active Limiter

Drive - Boost and compress the signal, helps make the signal stronger, adds harmonics

Other

Enable - Standard fader with 3 modes: Bypass effect, On Effect, Off Effect

Soft Bypass - Soft Bypass with smoothed fade in/out functionality

Patch Browser - Select and open factory patches, save your own patches with unique patterns

Blend - Blend Dry/Wet functional of incoming and processed signals

Pre-Gain - Gain of incoming signal
Gain - Output Level Gain

UPDATE v. 2.0.1:

• Filter keytrack & Self-Oscilltion now can be controllable by midi notes from the Reason sequencer (piano roll). ASVF-212 now accept incoming notes from the device sequencer track.
  For Oscillator keytrack: Just create ASVF-212, set Notes frequency mode, select in context menu “New Note Lane” and create midi clip with sequence for self-oscillated signal.
  For Filter keytrack: Just create ASVF-212, set Frequency mode, select in context menu “New Note Lane” and create midi clip with sequence for filter keytrack.

UPDATE v. 2.0:
- New bigger panel (3U height) with new GUI design
- Self-Oscillation mode (set Filter Q = 100%, that run self-oscillation if option is on)
- Filter Keytracking. Activate Key Note frequency mode, and play by midi keys with self-oscillated signal
- Filter Smoothing
- Envelope Follower works with main signal inputs, plus new external ENV.FLW inputs
- Individual Envelope Follower Amount control (was been controllable by LFO Affect)
- Filter Drive. Works like a overdrive with compressor. Can be active only as part of active Limiter.

v.1.0.1:
- L/R connections GUI bug fix,
- Rear panel connection type icons changed to True Stereo / Double Mono
- minor GUI changes