Class: Noyes::BentCentMarker

Inherits:
Object
  • Object
show all
Defined in:
lib/ruby_impl/bent_cent_marker.rb

Overview

Determines whether a PCM frame is speech or not using Bent Schmidt-Nielsen’s algorithm. Basically, it’s an energy-based detector where the background noise level is constantly estimated. You probably don’t want to use this class directly. Most of the time you’ll want to use SpeechTrimmer, which uses this class.

The pcm data should be in 100 millisecond chunks. For example, At 8000 Hz there should 80 frames of pcm.

Instance Method Summary collapse

Constructor Details

#initialize ⇒ BentCentMarker

Returns a new instance of BentCentMarker.



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# File 'lib/ruby_impl/bent_cent_marker.rb', line 11

def initialize
  @adjustment = 0.003
  @average_number = 1.0
  @background = 100.0
  @level = 0.0
  @min_signal = 0.0
  @threshold = 10.0
end

Instance Method Details

#<<(pcm) ⇒ Object

Takes a centisecond worth of pcm values and indicates whether it looks like speech. This information is typically used by SpeechTrimmer.



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# File 'lib/ruby_impl/bent_cent_marker.rb', line 31

def << pcm
  is_speech = false
  current = logrms pcm
  if current >= @min_signal
    @level = ((@level * @average_number) + current) / (@average_number + 1)
    if current < @background 
      @background = current
    else
      @background += (current - @background) * @adjustment
    end
    @level = @background if (@level < @background)
    is_speech = @level - @background > @threshold
  end
  is_speech
end

#logrms(pcm) ⇒ Object

Take the log rms of an array of pcm values.



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# File 'lib/ruby_impl/bent_cent_marker.rb', line 21

def logrms pcm
  sum_of_squares = 0.0
  pcm.each {|sample| sum_of_squares += sample * sample}
  rms = Math.sqrt sum_of_squares / pcm.size;
  rms = Math.max rms, 1
  Math.log(rms) * 20
end