Contents

module SPCore
# Provide resampling method using polynomial upsampling and discrete filtering
# for downsampling.
class HybridResampling
  def self.resample input, sample_rate, upsample_factor, downsample_factor, filter_order
    raise ArgumentError, "input.size is less than four" unless input.size >= 4
    raise ArgumentError, "upsample_factor is not greater than 1" unless upsample_factor > 1
    raise ArgumentError, "downsample_factor is not a Fixnum" unless downsample_factor.is_a?(Fixnum)
    raise ArgumentError, "downsample_factor is not greater than 1" unless downsample_factor > 1
    raise ArgumentError, "sample_rate is not greater than 0" unless sample_rate > 0
    
    upsampled = PolynomialResampling.upsample input, sample_rate, upsample_factor
    
    needed_samples = upsampled.size % downsample_factor
    if needed_samples == 0
      upsampled += Array.new(needed_samples, 0.0)
    end
    
    target_rate = sample_rate * upsample_factor / downsample_factor
    cutoff = (target_rate < sample_rate) ? (target_rate / 2.0) : (sample_rate / 2.0)

    filter = SincFilter.new(
      :sample_rate => (sample_rate * upsample_factor), :order => filter_order,
      :cutoff_freq => cutoff, :window_class => NuttallWindow
    )
    filtered = filter.lowpass(upsampled)
    return Array.new(filtered.size / downsample_factor){ |i| filtered[i * downsample_factor] }
  end
end
end

Version data entries

5 entries across 5 versions & 1 rubygems

Version	Path
spcore-0.1.7	lib/spcore/resampling/hybrid_resampling.rb
spcore-0.1.6	lib/spcore/resampling/hybrid_resampling.rb
spcore-0.1.5	lib/spcore/resampling/hybrid_resampling.rb
spcore-0.1.4	lib/spcore/resampling/hybrid_resampling.rb
spcore-0.1.3	lib/spcore/resampling/hybrid_resampling.rb