Anatomy of a CHOP

Inside a CHOP

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• A CHOP contains a set of channels defined over a start-end interval.
• The channels of a CHOP can represent motion, MIDI, audio, color maps, rolloff curves or lookup tables.
• Each channel is one array of raw samples, which is simply a list of numbers.
• Each channel of a CHOP has a channel name that can be set by the user.
• The group of CHOP channels is known as a clip.
• A CHOP contains a clip plus control parameters, a sample rate, some on/off flags, and a start/end interval.
• The CHOP can have any start/end indexes. All channels in a CHOP share the same start-end interval.
• The interval goes from the start position to the end position.
• The interval of a CHOP is not restricted to be the length of the animation.
• Each CHOP has a sample rate, used if the CHOP contains time-dependent motion or audio data.
• Audio has a high sample rates when compared to animated motion.

CHOP Inputs, Parameters and Outputs

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• CHOPs have "parameters" used to define the data, plus the data channels, which are input/output from the CHOP as its data stream.
• The CHOP parameters are usually constant-valued, but can be time-dependent expressions.
• Each CHOP receives channels at its inputs. When the CHOP cooks, the channels of the inputs are combined. The CHOP outputs the resulting channels to other CHOPs.
• CHOPs output their data channels as arrays of numbers, not interpolated segments. Some CHOPs retain interpolated segments internally, but all CHOPs always output their data as raw samples.
• If the CHOP's inputs are not changing and the control parameters are not time-dependent, the CHOP will be non-time-dependent and it will not cook every time the animation frame advances.
• Some CHOPs have Local Variables:
  $I (the array index within the CHOP), $C (the channel number within the CHOP)
• Some CHOPs output or use CHOP attributes, such as channels grouped as quaternion rotation channels.

Parts of a CHOP

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• Each CHOP has a set of parameters.
• CHOPs' parameters can be expressed in different units: samples (indexes), frames or seconds. These units are selected by the user in a menu to the right of such parameters.
• Each CHOP has flags:
  • The Graph flag marks the CHOP to be displayed in the Graph of the CHOP Editor.
  • The Export flag causes the CHOP channels to override channels of objects, SOps.
  • The Lock flag causes the CHOP can be locked and hand-edited. The Channel Editor is the interactive editor of parameter channels in CHOPs.
  • The Bypass flag is a convenient way for a CHOP's effect to be disabled.
• Each CHOP has an info pop-up menu accessible by middle-mouse clicking on the CHOP. This lists channel names and values, sample rate and interval.
• Each CHOP has a comment field.

CHOP Networks

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• CHOPs are arranged in OP networks in components, where CHOP outputs are connected to the inputs of other CHOPs.

Importing / Exporting CHOP Channels

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Object, SOP and COP Channels Imported from CHOPs

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Parameters of SOPs, TOPs and objects (components) are able to get values from CHOP channels with expressions like the following:

 chop(CHOPchannelpath)
 chopi(CHOPchannelpath, index

However, exporting is preferred where possible. It is faster and involves less typing.

CHOPs Exported to Component, SOP and TOP Channels

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• CHOP data channels are exported to Components, SOPs, etc. to drive their parameters. CHOPs can be exported to any TouchDesigner parameter.
• Each CHOP has an Export flag (and an Export Prefix, infrequently used), causing the CHOP to attach its channels to Components, SOPs, TOPs and so on.
• The Export flag and Export Prefix are used to connect channels of an object or SOP directly to a CHOP. It uses automatic matching of channels names. For example, a CHOP "tx" channel could map to an Geometry Component's tx parameter.
• When a CHOP exports to an object, SOP or TOP, the latters' channels are said to be overridden. An OP's Override menu lists what is overridden.

Channel Index and Value

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• The horizontal axis is called the i-axis or the index-axis.
• The vertical axis is called the v-axis or the value-axis.
• An index is a point along the i-axis,denoted by i.
• A value is a point along the v-axis, denoted by v.
• A sample is an index-value pair (i,v). i.e. the value of a channel at a certain index.
• A sample is made of a sample index and a sample value.
• An interval is an index range, which goes from a start index to an end index.
• A value range goes from a start value to an end value.
• The index duration is the end index minus the start index + 1.
• CHOP data channels are arrays of raw samples, in 32-bit floating point format.
• Channels in a CHOP may be control (parameter) channels or data channels. CHOPs manupulate the data channels.
• CHOPs can be evaluated at integer and non-integer indexes.
• Frame is used when the index corresponds to time.
• When speaking of animation frames, you can refer to start frame, end frame and frame range.

CHOPs for Audio

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• Audio File In CHOP
• Audio Movie CHOP
• Audio Play CHOP
• Audio Device In CHOP
• Audio Device Out CHOP