Class: Digiproc::Factories::FilterFactory

Inherits:
Object
  • Object
show all
Defined in:
lib/factories/filter_factory.rb

Defined Under Namespace

Classes: Filters

Class Method Summary collapse

Class Method Details

.filter_for(type:, wc: nil, wo: nil, bw: nil, transition_width: nil, stopband_attenuation:) ⇒ Object

Give requirements of the filter:

type
String

Accepts: ‘highpass’, ‘lowpass’, ‘bandpass’, ‘bandstop’

wc
Float

cutoff frequency in radians

wo
Float

center frequency in radians

bw
Float

bandwidth in radians

transition_width
Float

in NORMALIZED FREQUENCY, ie 0 to 1 scale, where 1 = Sampling Frequency (should be changed to rad for consistency)

stopband_attenuation
Numeric

level of stopband in decibles

Also Note:

Digiproc::LowpassFilter

requires wc, not wo or bw

Digiproc::HighpassFilter

requires wc, not wo or bw

Digiproc::BandpassFilter

requires wo and bw, not wc

Digiproc::BandstopFilter

requires wo and bw, not wc

NOTE: This factory makes all sizes odd in ensure all types of filters will work (ie an even number of values will not allow a highpass filter, an anti-symmetric odd will not allow a lowpass, etc.) Available windows: Digiproc::RectangularWindow, Digiproc::HanningWindow, Digiproc::HammingWindow, Digiproc::BlackmanWindow



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# File 'lib/factories/filter_factory.rb', line 25

def self.filter_for(type: , wc: nil, wo: nil, bw: nil, transition_width: nil, stopband_attenuation: )
    window = nil
    size = 0
    if stopband_attenuation < 21
        window = Digiproc::RectangularWindow
        size = make_odd(0.9 / transition_width)
    elsif stopband_attenuation < 40
        window = Digiproc::HanningWindow
        size = make_odd(3.1 / transition_width)
    elsif stopband_attenuation < 50
        window = Digiproc::HammingWindow
        size = make_odd(3.3 / transition_width)
    else
        window = Digiproc::BlackmanWindow
        size = make_odd(5.5 / transition_width)
    end

    case type.to_s.downcase
    when 'lowpass'
        return Filters::lowpass.new(wc: wc, size: size, window: window)
    when 'highpass'
        return Filters::highpass.new(wc: wc, size: size, window: window)
    when 'bandpass'
        return Filters::bandpass.new(wo: wo, bw: bw, size: size, window: window)
    when 'bandstop'
        return Filters::bandstop.new(wo: wo, bw: bw, size: size, window: window)
    else
        raise ArgumentError.new('Filter types include: lowpass, highpass, bandpass, bandstop')
    end
end

.make_odd(num) ⇒ Object

Input Numeric, output closest round integer >= to input



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# File 'lib/factories/filter_factory.rb', line 58

def self.make_odd(num)
    n = num.round 
    n += 1 if n.even?
    n
end