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filterdesign Reference

Create a filter specification

filterdesign

Description

Use the filterdesign object to create a dictionary containing a specification for a filter that can be realized by several other objects including the cascade~ object.

Arguments

None.

Attributes

frequency [2 floats]

Filter cutoff frequencies specified in units defined by the units attribute. For lowpass and highpass filters a single frequency will be used to define the cutoff. For bandpass and bandstop filters two frequencies are required.

name [symbol]

Name to which the output dictionary is bound

order [int]

The order of the filter, which is to say the number of poles and zeroes. For reference, the biquad~ object is a second-order filter (2 poles and 2 zeroes).

passband_ripple [float]

Magnitude ripple in the passband for Chebyshev Type 1 filters in decibels. Higher amounts of ripple will provide a narrower transition band given a constant order for the filter.

response [symbol]

Filter response shape

Possible values:

'lowpass' ( Low frequencies pass through, high frequencies are attenuated )
'highpass' ( High frequencies pass through, low frequencies are attenuated )
'bandpass' ( A band of frequencies pass through, low and high frequencies are attenuated )
'bandstop' ( A band of frequencies are attenuated, low and high frequencies pass through )

samplerate [int]

Samplerate used when unit attribute is set to hertz. If the samplerate is set to zero then MSP's samplerate will be used.

sos_output [int]

Inclusion of coefficients for second-order-sections in the output dictionary. This is the native format used by cascade~, zplane~, and filtergraph~.

stopband_attenuation [float]

Minimum attenuation in Chebyshev Type 2 filter stopband in decibels. For given order of filter, greater attenuation results in a wider transition band and less attenuation in the stopband results in a narrower transition band.

tf_output [int]

Include single-section transfer function coefficients in the output dictionary. This representation works well for low-ordered filters but quickly becomes subject to floating-point precision roundoff as the order of the filter increases.

topology [symbol]

The organization of the zeroes and poles used to realize the filter.

Possible values:

'butterworth' ( Gentle transition, flat passband, monotonically decreasing stopband )
'chebyshev-1' ( Steepest transition, definable ripple in passband, monotonically decreasing stopband )
'chebyshev-2' ( Moderate transition, flat passband, definable ripple in the stopband )

units [symbol]

Units of measurement for specifying frequencies

Possible values:

'hertz' ( Cycles per second, based on the samplerate attribute )
'normalized' ( Range from 0.0 to 1.0; 1.0 is the nyquist frequency )
'radians' ( Range from 0.0 to pi; pi is the nyquist frequency )

zpk_output [int]

Include zeroes-poles-gain representation in the output dictionary. Zeroes-poles-gain (ZPK) provides a more accurate representation of the filter's response than the single-section transfer function (see tf_output attribute) for higher-order filters. If calculating coefficients for second-order-sections (see sos_output attribute) the ZPK representation is calculated as an intermediary stage.

Common Box Attributes

Messages

bang

Sending a bang will generate the filterdesign dictionary using current attributes and send it out the first outlet.

(mouse)

Double-click the filterdesign object to open a dictionary editor window and view or edit the current attributes.

Output

dictionary

A filterdesign dictionary containing the specified filter characteristics.

See Also

Name Description
Sound Processing Techniques Sound Processing Techniques
filterdetail
plot~
cascade~
Audio Filtering Audio Filtering