chromaprint-fixed/src/silenceRemover.coffee

A JavaScript implementation of AcoustID Chromaprint

@chromaprint ?= {}
 
# Gets a function for removing silence from a buffer. It can be configured with
# a silence threshold. The window is also configurable (see the filter function
# below), but defaults to 55, which, I am told, is 5ms at 11025 Hz.
silenceRemover = (threshold, window = 55) ->
  # The filter returns a function that returns true if the average ever passes
  # above the threshold. The window is the starting point when summing up the
  # bytes for the average.
  filter = (window) ->
    finished = false
    (byte, index) ->
      finished or= ((window += byte) / (index + 1)) > threshold
  # This function returns what it's given only if the average has s
  # The returned function takes an array of bytes, only returns those that occur
  # after the average has surpassed the silence threshold.
  (input) -> input.filter filter(window)

@chromaprint.silenceRemover = silenceRemover