makefilter

Create a “filter” to alter PField control data, reading from one pfield-handle or table-handle and passing the altered data through another pfield-handle.

Synopsis

pfield = makefilter(input_handle, “filter_type”, arg1, arg2, …)

Parameters inside the [brackets] are optional.

Description

makefilter returns a pfield-handle that will deliver data by applying an operation defined by “filter_type” to the data coming through the input-handle variable. The input_handle variable can be any of the PField-derived variables in RTcmix, such as a table-handle (see maketable) or another pfield-handle (see makeconnection, makeLFO or makerandom). The arguments vary depending on each filter_type.

Many of the arguments for makefilter may themselves also be pfield-handles.

Arguments

input_handle

This is pfield-handle variable referring to a data stream, possibly from an external device or interface or an internal PField data-generating process.
filter_type

This string value (i.e. enclosed in “double quotes” in the scorefile) determines what kind of ‘filter’ will be used to transform the values coming through the input_handle. The pfield-handle returned from the makefilter command will refer to this transformed data stream.
arg1, arg2, …

The arguments that are relevant for each filter type. These will determine how the particular filter operates to transform the data. See documentation for each type below.

Filter Types

clip

The clip filter will This limits the incoming pfield values to the range defined by min and max, which both can be dynamic. The syntax is:
```
pfield = makefilter(input_pfield, "clip", min[, max])
```
Data coming through the input_pfield variable less then the value min will be reset to the value min. Similarly, data greater than the value max (if present) will be set to max.
constrain

The constrain filter works with two data streams, one being an incoming set of pfield values (as with all the makefilter filter types), and the other being a table_handle p-field referring to an existing table of values. The syntax is:
```
pfield = makefilter(input_pfield, "constrain", table_handle, strength)
```
For each value coming through the input_pfield variable, this filter will return the nearest numerical value in the table_handle table. The strength parameter (from 0 to 1) is a measure of how closely the filter constrains the pfield to the table value. A strength value of 0 means no constraint (i.e., you get back the original pfield value); a strength of 1 means you get the table value; a strength of 0.5 means you get a value midway between the pfield and table values. strength can be time-varying.
delay

The delay filter introduces a time delay into the data stream coming through the input_pfield variable. The syntax is:
```
pfield = makefilter(input_pfield, "delay", time)
```
time is the length of the delay (in seconds). The delay is relative to when the data appears through the input_pfield.
fitrange

The fitrange filter will take data in the range [0.0, 1.0] or [-1.0, 1.0] and expand it to a specified range. The syntax is:
```
pfield = makefilter(input_pfield, "fitrange", min, max[, "bipolar"])
```
Data coming through the input_pfield variable in the range [0.0, 1.0] will be expanded and transformed to fit the range [min, max]. When the input data is 0.0, the output will be min. Input data at 1.0 will output max. If the optional “bipolar” string argument is given, then the fitrange filter assumes that the input data will be in the [-1.0, 1.0] range — when the input is -1.0, then min will be the output; input of 1.0 will yield max.
invert

The invert filter will take data from an input p-field and invert the values, i.e. all values are mirrored around a center value. The syntax is:
```
pfield = makefilter(input_pfield, "invert"[, center])
```
By default, the center value (y-axis center of symmetry) is a point halfway between the min and max table values. If the optional second center argument is present, this will be used as the vertical center of symmetry.
map

The map filter sets up a ‘transfer function’ for data coming through an input p-field. The syntax is:
```
pfield = makefilter(input_pfield, "map", transfer_table[, inputMin, inputMax])
```
The operation of the map filter is a simple table-lookup transfer function. The transfer function itself is set using the transfer_table table-handle (see maketable for how to create these tables). Values then coming in through the input_pfield parameter are treated as X-locations in the transfer_table, and the corresponding Y-value for a given X-location will be returned through the pfield variable. The input data stream can be scaled to match the X-range of the transfer_table table using the optional inputMin and inputMax parameters.
quantize

The quantize filter will transform data coming through the input_pfield variable by shifting each input value to an integer multiple of the quantize_value. The syntax is:
```
pfield = makefilter(input_pfield, "quantize", quantize_value)
```
All data values coming through the input_pfield will be rounded to the nearest integer multiple (both positive and negative) of the quantize_value and then output through the data stream associated with the pfield variable. A value exactly 0.5 between two successive multiples of quantize_value will be rounded to the upper multiple. This is the inverse of the interpolation procedure used in the “smooth” filter.
smooth

The smooth filter type will linearly interpolate values coming through the input_pfield variable depending on the rate set by lag. This means that large jumps in input will be ‘smoothed’ into a series of smaller value jumps in the output. The syntax is:
```
pfield = makefilter(input_pfield, "smooth", lag[, initial_value])
```
The filter operates by applying a one-pole linear filter to the input values. lag is a percentage that determines how quickly (i.e. the number of interpolation steps) the filter will jump from one value to the next for a given input sequence. By default, it will start from 0 when initialized. Set the optional initial value value to prevent a swoop to the input pfield value at the start.

Examples

rpfield = makerandom("even", 7.0, 0.0, 100.0)
smpfield = makefilter("smooth", 20)
qpfield = makefilter("quantize", 20)
rpfield = makefilter("fitrange", 0.0, 1.0)

The makerandom scorefile command will output random numbers between 0.0 and 100.0 at a rate of 7 times/second (7.0 Hz). Three different makefilter commands modify that data. Associated with the smpfield variable will be data that is ‘smoothed’ by 20% – large jumps in the random values will be “filled in” by interpolated values. The qpfield stream will deliver data that consists of the closest integer multiple of 20 (the output will be [0.0, 20.0, 40.0, 60.0, 80.0, 100.0] depending on the value of the input). rpfield will take the [0.0, 100.0] range and scale it to fit between 0.0 and 1.0.

table = maketable("literal", "nonorm", 0, 8.00, 8.02, 8.04, 8.05, 8.07)
rpfield = makerandom("even", 10.0, 8.00, 8.07)
pitches = makefilter(rpfield, "constrain", table, 1.0)

This will take the random numbers (generated 10 times each second) coming through rpfield and cause them to generate one of the specific values in the table set of values. The result will be assigned through the p-field variable pitches

table = maketable("expbrk", 1000, 0.0001, 1000, 1.0)
newpfield = makefilter("invert", table)