Audio Filter CHOP

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The Audio Filter CHOP removes low frequencies, high frequencies, both low and high, or removes a mid-frequency range.

A Low pass filter removes the higher frequencies of a sound, while a high pass filter reduces the bass of the sound. A band pass filter is used to extract a frequency range (i.e. extracting a person's voice from background noise) and a band reject filter is used to cut out a frequency range.

If a certain frequency lies outside the pass band, sounds at that frequency will be reduced in magnitude. The farther outside the pass band the frequency is, the more it will be reduced.

The Cutoff frequency is also known as the "half-power" frequency. A wave at the cutoff frequency will be reduced to half power.

The Rolloff of a filter determines how quickly the drop occurs at its Cutoff frequencies. A low rolloff will produce a gradual filter falloff (more of the sounds outside the frequency range are heard), and a high rolloff will produce a sharp filter falloff.

Refer to audio filter for more insight.

You can see the effects of the Audio Filter CHOP by passing it white noise from an Oscillator CHOP and sending the result to an Audio Spectrum CHOP. The Audio Filter CHOP is implemented with a 4-pole filter internally.

Moving the Dry / Wet parameter to Dry will bring back the incoming signal un-affected.

Input 2: See Cutoff Modulation Channels

See Audio Para EQ CHOP, Audio Band EQ CHOP, Audio Spectrum CHOP, Audio Dynamics CHOP


Parameters - Filter Page

Filter filter - - The filter type:

  • Low Pass lowpass - All frequencies below the High Cutoff are passed through the filter (the "pass band").
  • High Pass highpass - All frequencies above the Low Cutoff are passed through.
  • Band Pass bandpass - All frequencies between the Low and High Cutoff are passed through.
  • Band Reject bandreject - All frequencies above the High Cutoff and below the Low Cutoff are passed though.

Cutoff Units units - - The filter cutoff frequency can be expressed in Hz (menu set to Frequency) or power-of-10 (menu set to Logarithmic). It enables one of the next 2 Filter Cutoff parameters.

  • Logarithmic logarithmic -
  • Frequency frequency -

Filter Cutoff (Hz=10**val) cutofflog - The filter cutoff frequency expressed in power-of-10, where value 0 translates to 1 Hz (10**0), value 1 is 10 Hz (10**1), value 2 is 100 Hz (10**2), value 3 is 1000 Hz, value 4 is 10,000 Hz, value 4.5 is 31,623 Hz. The parameter in this form gives more meaningful range in relation to human hearing, as increasing the parameter by 1 raises the frequency by about 3 octaves.

Filter Cutoff (Hz) cutofffrequency - The filter cutoff frequency expressed in Hz (cycles per second). This parameter set to 1000 has exactly the same effect as the above parameter set to 3.

Filter Resonance resonance - Increasing the resonance will boost the loudness of the passed frequencies near the cutoff frequency.

Roll-Off (dB per Octave) rolloff - Rolloff determines how much the levels decrease near the cutoff frequency. This parameter will make it decrease by 12 decibels (dB) per octave, to, more extremely, 24 decibels per octave. 12 and 24 decibels correspond to levels of about 1/4 and 1/16.

Dry / Wet Mix drywet - As this parameter is reduced from 1 (Wet) toward 0 (Dry), it removes the effect of the filter.

Parameters - Common Page

Time Slice timeslice - Turning this on forces the channels to be "Time Sliced". A Time Slice is the time between the last cook frame and the current cook frame.

Scope scope - To determine which channels get affected, some CHOPs use a Scope string on the Common page.

Sample Rate Match srselect - - Handle cases where multiple input CHOPs' sample rates are different. When Resampling occurs, the curves are interpolated according to the Interpolation Method Option, or "Linear" if the Interpolate Options are not available.

  • Resample At First Input's Rate first - Use rate of first input to resample others.
  • Resample At Maximum Rate max - Resample to the highest sample rate.
  • Resample At Minimum Rate min - Resample to the lowest sample rate.
  • Error If Rates Differ err - Doesn't accept conflicting sample rates.

Export Method exportmethod - - This will determine how to connect the CHOP channel to the parameter. Refer to the Export article for more information.

  • DAT Table by Index datindex - Uses the docked DAT table and references the channel via the index of the channel in the CHOP.
  • DAT Table by Name datname - Uses the docked DAT table and references the channel via the name of the channel in the CHOP.
  • Channel Name is Path:Parameter autoname - The channel is the full destination of where to export to, such has geo1/transform1:tx.

Export Root autoexportroot - This path points to the root node where all of the paths that exporting by Channel Name is Path:Parameter are relative to.

Export Table exporttable - The DAT used to hold the export information when using the DAT Table Export Methods (See above).

Cutoff Modulation Channels Input

The second input is the Cutoff Modulation Channels, which allows the filter parameters to be changed within the CHOP's time slice interval (typically 1/60 sec). This prevents audible stepping of the parameters that you are changing quickly.

You can send in a channel called cutofffrequency to override the value of the parameter. You would do this if you want to adjust the cutoff frequency very quickly. The parameter can only change as fast as the timeline rate, typically 1/60 seconds. Changed quickly, the stepping in frequency is noticeable. To improve on that, you would send a cutofffrequency channel in that is at a higher sample rate, like 400, which you can set in a CHOP like an LFO CHOP.

Operator Inputs

  • Input 0 -
  • Input 1 -

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Operators that have 1 or more input, like a Math CHOP, are called filters. See Generator.

An Operator Family which operate on Channels (a series of numbers) which are used for animation, audio, mathematics, simulation, logic, UI construction, and many other applications.

A Time Slice is the time from the last cook frame to the current cook frame. In CHOPs it is the set of short channels that only contain the CHOP channels' samples between the last and the current cook frame.

A parameter in most CHOPs that restricts which channels of that CHOP will be affected. Normally all channels of a CHOP are affected by the operator.

samples-per-second of a CHOP. Each CHOP in your network has a sample rate, whether it is used or not. The overall timeline has a "frame rate", which is the number of animation frames per second, generally your monitor display frequency.

Exporting is the connection of CHOP channels to parameters of operators. The output of each exporting CHOP is one or more channels, active only while the CHOP Viewer is on. The current value of a channel can be exported to a parameter of any operator, overriding that parameter's value. See Parameter.

An Operator Family that manipulates text strings: multi-line text or tables. Multi-line text is often a command Script, but can be any multi-line text. Tables are rows and columns of cells, each containing a text string.

The location of an operator within the TouchDesigner environment, for example, /geo1/torus1, a node called torus1 in a component called geo1. The path / is called Root. To refer instead to a filesystem folder, directory, disk file or http: address, see Folder.

Parameters in TouchDesigner are an operator's settings (numbers, menus, flags, strings, paths) which the user can alter. Parameters for any operator can be opened by right-clicking on the operator and selecting "Parameters..." A currently selected operator's parameters can be viewed in a Network Editor by pressing the keyboard shortcut 'p'.

TouchDesigner is a hierarchy of components. "root" is the top-most network in the hierarchy. The Path is simply /. A typical path is /project1/moviein1.