Interleaved Unpacking...

gistfile1.rb

    # This takes about 2s for a 53Mb file.
    bytes = audio_file.read_into(audio_buffer)

    # This takes less than a second, BUT the data is interleaved
    # (left, right, left, right, left, right, etc)
    self.audio_data = audio_buffer.unpack('s*')
    
    # Less than a second.
    self.left_channel = NArray.float(2, audio_data.size)
    self.right_channel = NArray.float(2, audio_data.size)
    
    # This loop takes about 40-50 seconds. Rewriting it to eliminate
    # all division and multiplication shaves about 10s off that time.
    0.upto(audio_data.size/2-1) do |i|
      time = i.to_f / audio_file.rate
      # First array stores time offset of sample
      left_channel[0, i] = time
      right_channel[0, i] = time
      
      # Second array stores sampled data
      left_channel[1, i] = audio_data[i*2]
      right_channel[1, i] = audio_data[i*2+1]
    end

    # BUT!
    # 
    # If I could avoid the Ruby loop altogether, and let something
    # like NArray's constructors handle it, it's a 10x speedup. For
    # example:
    # 
    # interleaved_data = NArray[self.audio_data]
    # 
    # Takes less than 4 seconds! This is because we're not looping in
    # Ruby, but letting C handle the grindy stuff. However, the data
    # is interleaved, making it useless for processing rationally. :-/
    # I can separate it back out with another loop, but guess how long
    # that takes....