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This realtime chop is used to manually tap the beat of a piece of music, and automatically generate a repeating ramp or pulse that continues to keep time with the music after the taps stop.
The CHOP computes the length of time (the period) of a beat. It can output five channels: a ramp from 0 to 1, a beat pulse, a beat count, and a constant channel containing the period.
The input must contain two channels, a Listen channel followed by a Tap channel. Often these channels are just two on/off keys on the computer keyboard (from the Keyboard chop), or two keys on a MIDI keyboard (from the Midi In chop). "On" must be greater than zero, and "off" must be zero or less.
When the Listen channel goes on, it means that you desire to change the tempo, and the CHOP is ready to record the user’s taps. After Listen goes on, the first tap on the Tap channel changes the output. A time slice or frame is output at the current frame, containing the beat information.
The next taps change the period of the beat, which is the length of the chop. The beat period is computed by taking the average time between taps. While the Listen channel is off, the output of the chop does not change.
If the Beat channel pulses are longer than one frame, only the time of the first sample matters.
To produce multiples of the tempo (double, half, quarter, etc.), use the Tempo Scale menus to select a range of tempos. Tempos from 1/8th to 8x the tapped tempo can be produced.
Hit the Tap channel at any time to synch the ramp to start at the current frame.
Lower/Upper Tempo Scale
Allows a range of beat channels from 1/8th of the input tempo to 8× the tempo.
Beat outputs either a time slice or one frame.
Resets the ramp on all taps, the first tap, or none.
If a tap occurs close to a beat, do not reset the ramp if within the grace period. The units are based on ramp values; 0.1 means a grace period of ramp values above 0.9 and less than 0.1.
Timer Ramp Name
This channel is a ramp from 0 to 1. The position within the beat cycle is represented as a value from 0 (start of beat) to 1 (end of beat).
Timer Pulse Name
This channel outputs a 1-sample pulse at the start of the ramp cycle.
Cycle Count Name
This channel counts the number of beats since the first tap. Re-synching the beat will reset this count to zero.
The name of the channel which contains the value of the period. Depending on the "Units" parameter in the Common page, it will be in Seconds, Frames or Samples.
Period Start Name
The name of the channel which contains the start sample/frame/time of the current ramp.
The sample rate of the output channels.
Some of these parameters may not be available on all CHOP nodes.
To determine which channels get affected, some CHOPs have a scope string. Patterns can be used in the scope, for example
* (match all), and
? (match single character).
The following are examples of possible channel name matching options:
Matches a single channel name.
chan3 tx ty tz
Matches four channel names, separated by spaces.
Matches each channel that starts with
Matches each channel that has
foot in it.
? matches a single character.
t? matches two-character channels starting with t.
Matches number ranges giving
[xyz]matches three characters, giving channels
Sample Rate Match
The Sample Rate Match Options handle cases where multiple input CHOPs’ sample rates are different.
Resample At First Input’s Rate
Use rate of first input to resample others.
Resample At Maximum Rate
Resample to highest sample rate.
Resample At Minimum Rate
Resample to the lowest sample rate.
Error if Rates Differ
Does not accept conflicting sample rates.
The units for which time parameters are specified.
For example, you can specify the amount of time a lag should last for in seconds (default), frames (at the Houdini FPS), or samples (in the CHOP’s sample rate).
When you change the Units parameter, it does not convert the existing parameters to the new units.
Time Slicing is a feature which boosts cooking performance and reduces memory usage. Traditionally, CHOPs calculate the channel over its entire frame range. If the channel does need to be evaluated every frame, then cooking the entire range of the channel is unnecessary. It is more efficient to calculate only the fraction of the channel that is needed. This fraction is known as a Time Slice.
Causes the memory consumed by a CHOP to be released after it is cooked and the data passed to the next CHOP.
The Export prefix is prepended to CHOP channel names to determine where to export to.
For example, if the CHOP channel was named
geo1:tx, and the prefix was
/obj, the channel would be exported to
You can leave the Export Prefix blank, but then your CHOP track names need to be absolute paths, such as
Every CHOP has this option. Each CHOP gets a default color assigned for display in the Graph port, but you can override the color in the Common page under Graph Color. There are 36 RGB color combinations in the Palette.
Graph Color Step
When the graph displays the animation curves and a CHOP has two or more channels, this defines the difference in color from one channel to the next, giving a rainbow spectrum of colors.