The Protostar's filter is a multimode circuit with a slope of -12 dB or -24 dB per octave and four characteristics, in detail low-pass, band-pass, high-pass and notch.
Values for the cutoff frequency and resonance can be set manually. Additionally, the cutoff can be modulated by the integrated LFO, an Envelope Follower or the control voltage input.

The LFO comes with parameters for speed and modulation depth, both are controllable via CV inputs. The LFO signal can be tapped off another jack of the Protostar's patch bay.
The Envelope Follower is editable in its threshold as well as attack and release times.

The ladder share one potentiometer. A bipolar knob alters the modulation value applied to the cutoff frequency. Again, the signal of the Envelope Follower can be tapped off the patch bay, but here you have two connectors for normal and inverted phase. Using the sidechain input, musicians can run external audio signals trough the Envelope Follower.

The Protostar's compressor comes with knobs for work intensity and the dry / wet mix.
Send and Return jacks allow to tie-in an external effect. Furthermore, an expression pedal can be connected to the unit. Thanks to the patch bay, it is possible to combine the foot controller with several parameters. Last but not least, the Protostar contains a feedback loop, which can only be influenced by control voltages.

KNOBS

Attack - How fast the envelope will react
to the incoming signal. Controls both
attack and release.

Threshold - How sensitive the envelope is to the
incoming signal.

Env Amt - Attenuverter that controls how much
the envelope will affect the frequency of
the filter, either negatively or positively.

Resonance - Synonomous with feedback or Q,
this is a boost of the frequencies around the
frequency cutoff.

Freq - Also known as cutoff, this knob's
position dictates the resting place of the
frequency cutoff.

LFO Rate - Make the LFO go faster or slower
with this knob.

LFO Amt - How much the LFO will affect the
frequency cutoff.

Compression - End of chain compressor squashes
the wet signal to suppress unwanted honks, and
resonant oddities.

Dry / Wet - Amount of unaffected vs. affected signal
coming through the output.

Sidechain - Direct input to the envelope follower.
Normalled to the input, use this to have the
envelope follow an external source.

Exp Out - Output for the expression pedal
input. Exp isn't connected to any control
internally and must be patched.

- Env Out - Always sending +5V until the
envelope is triggered, bringing the voltage
down to 0V and back.

+ Env Out - Sends a CV signal following the
envelope. Signal is 0V to +5V.

LFO Out - Constantly sends the triangle
wave LFO CV signal, reacts to LFO rate knob.

LFO Rate - CV input for control over LFO rate.
Sensitivity adjustable with internal trim pot.

LFO Amt - CV input for control over LFO amt.

Freq - CV Input for control over cutoff frequency.

Feedback - CV input for control over resonance.

Expression Input (back panel) - Plug a TRS
cable from any expression pedal into this, patch
the exp out to what you want to contol, and
express yourself.