Class: SynthBlocks::Core::StateVariableFilter

Inherits:
Object
  • Object
show all
Defined in:
lib/synth_blocks/core/state_variable_filter.rb

Overview

Simple State Variable filter

source: http://www.musicdsp.org/en/latest/Filters/23-state-variable.html More info: https://www.earlevel.com/main/2003/03/02/the-digital-state-variable-filter/

Instance Method Summary collapse

Constructor Details

#initialize(sfreq) ⇒ StateVariableFilter

Create new filter instance



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# File 'lib/synth_blocks/core/state_variable_filter.rb', line 11

def initialize(sfreq)
  @sampling_frequency = sfreq.to_f
  @delay_1 = 0.0
  @delay_2 = 0.0
end

Instance Method Details

#run(input, frequency, q, type: :lowpass) ⇒ Object

run the filter from input value [frequency] cutoff freq in Hz [q] resonance, from 0 to ... [type] can be :lowpass, :highpass, :bandpass and :notch



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# File 'lib/synth_blocks/core/state_variable_filter.rb', line 21

def run(input, frequency, q, type: :lowpass)
  # derived parameters
  q1 = 1.0 / q.to_f
  f1 = 2.0 * Math::PI * frequency.to_f / @sampling_frequency

  # calculate filters
  lowpass = @delay_2 + f1 * @delay_1
  highpass = input - lowpass - q1 * @delay_1
  bandpass = f1 * highpass + @delay_1
  notch = highpass + lowpass

  # store delays
  @delay_1 = bandpass
  @delay_2 = lowpass

  results = { lowpass: lowpass, highpass: highpass, bandpass: bandpass, notch: notch }
  results[type]
end