Lowpass Filter Node

Standard resonant lowpass filter with 12dB/octave rolloff. Frequencies below the cutoff pass through; frequencies above it are attenuated.

You can use this Node to create muffled audio, where only the lower frequencies are audible, and the rest are attenuated/muted (e.g. similarly to the sound of a loud bar, as heard from the outside, or from the bathroom).


How to Use

The Lowpass Filter Node needs a source audio signal connected to its audio input, to which it can apply the effect, and then output the result. The input audio signal can come from anywhere, as long as it's audible: an Audio File Node, Oscillator Node, Noise Generator Node all work. Click their output, then click the audio input of the Lowpass Filter Node to establish a connection.

Connect to an Audio Destination Node to listen to the output, and play your project if your audio source needs it.


Inputs

Audio Input

An audio signal to filter. For control signals, the Lowpass Filter Node adds an easing effect, causing suddenly changing control signals to become a moderate to fast transition, depending on the cutoff frequency.

Frequency-Control Input

A control signal to control the Frequency setting. You can also connect an audio signal, but keep in mind that it can cause the Lowpass Filter Node to become unstable and reset. See the technical details section below.

You can enable this input from node properties, or by connecting to it.

Resonance-Control Input

A control signal to automate the Resonance setting, from 0.0001 to 1000.

You can enable this input from node properties, or by connecting to it.


Settings

Frequency

The filter cutoff frequency, in Hz. Frequencies below this setting pass through, frequencies above are attenuated.

Resonance

Sets how peaked the frequency is around the cutoff. The greater the value, the greater the peak.

Filter Order

The order of the differential equation describing the filter. In simpler terms, when you increase the filter order, it’s essentially the same as chaining multiple Lowpass Filter Nodes.


Outputs

Audio Output

The filtered audio signal (or control signal).


Technical details

The Lowpass Filter Node is a digital biquad filter, and as such, it's possible for it to become unstable, e.g. in response to rapid frequency modulation. When this happens, the Lowpass Filter Node will attempt to reset itself every few seconds, to avoid remaining unstable forever. This auto-reset is done in real-time mode (i.e. when you play your project), but not during exporting. That is, if the filter becomes unstable while exporting, it may remain unstable until the end of the exported audio.

Note: the behavior of this auto-reset is mostly non-deterministic, and depends on several undocumented factors. Don't rely on it to produce "glitchy" audio. Instead, use a Gain Node with an LFO-controlled gain, or a similar amplitude modulation technique.