Class: WaveFile

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

Overview

WAV File Specification FROM ccrma.stanford.edu/courses/422/projects/WaveFormat/ The canonical WAVE format starts with the RIFF header: 0 4 ChunkID Contains the letters “RIFF” in ASCII form

(0x52494646 big-endian form).

4 4 ChunkSize 36 + SubChunk2Size, or more precisely:

4 + (8 + SubChunk1Size) + (8 + SubChunk2Size)
This is the size of the rest of the chunk
following this number.  This is the size of the
entire file in bytes minus 8 bytes for the
two fields not included in this count:
ChunkID and ChunkSize.

8 4 Format Contains the letters “WAVE”

(0x57415645 big-endian form).

The “WAVE” format consists of two subchunks: “fmt ” and “data”: The “fmt ” subchunk describes the sound data’s format: 12 4 Subchunk1ID Contains the letters “fmt ”

(0x666d7420 big-endian form).

16 4 Subchunk1Size 16 for PCM. This is the size of the

rest of the Subchunk which follows this number.

20 2 AudioFormat PCM = 1 (i.e. Linear quantization)

Values other than 1 indicate some
form of compression.

22 2 NumChannels Mono = 1, Stereo = 2, etc. 24 4 SampleRate 8000, 44100, etc. 28 4 ByteRate == SampleRate * NumChannels * BitsPerSample/8 32 2 BlockAlign == NumChannels * BitsPerSample/8

The number of bytes for one sample including
all channels. I wonder what happens when
this number isn't an integer?

34 2 BitsPerSample 8 bits = 8, 16 bits = 16, etc.

The “data” subchunk contains the size of the data and the actual sound: 36 4 Subchunk2ID Contains the letters “data”

(0x64617461 big-endian form).

40 4 Subchunk2Size == NumSamples * NumChannels * BitsPerSample/8

This is the number of bytes in the data.
You can also think of this as the size
of the read of the subchunk following this
number.

44 * Data The actual sound data.

Constant Summary collapse

CHUNK_ID = 
"RIFF"
FORMAT = 
"WAVE"
FORMAT_CHUNK_ID = 
"fmt "
SUB_CHUNK1_SIZE = 
16
PCM = 
1
DATA_CHUNK_ID = 
"data"
HEADER_SIZE = 
36

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(num_channels, sample_rate, bits_per_sample, sample_data = []) ⇒ WaveFile

Returns a new instance of WaveFile.



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# File 'lib/wavefile.rb', line 57

def initialize(num_channels, sample_rate, bits_per_sample, sample_data = [])
  if num_channels == :mono
    @num_channels = 1
  elsif num_channels == :stereo
    @num_channels = 2
  else
    @num_channels = num_channels
  end
  @sample_rate = sample_rate
  @bits_per_sample = bits_per_sample
  @sample_data = sample_data
  
  @byte_rate = sample_rate * @num_channels * (bits_per_sample / 8)
  @block_align = @num_channels * (bits_per_sample / 8)
end

Instance Attribute Details

#bits_per_sample ⇒ Object

Returns the value of attribute bits_per_sample.



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# File 'lib/wavefile.rb', line 352

def bits_per_sample
  @bits_per_sample
end

#block_align ⇒ Object (readonly)

Returns the value of attribute block_align.



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# File 'lib/wavefile.rb', line 352

def block_align
  @block_align
end

#byte_rate ⇒ Object (readonly)

Returns the value of attribute byte_rate.



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# File 'lib/wavefile.rb', line 352

def byte_rate
  @byte_rate
end

#num_channels ⇒ Object

Returns the value of attribute num_channels.



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# File 'lib/wavefile.rb', line 352

def num_channels
  @num_channels
end

#sample_rate ⇒ Object

Returns the value of attribute sample_rate.



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# File 'lib/wavefile.rb', line 353

def sample_rate
  @sample_rate
end

Class Method Details

.open(path) ⇒ Object 



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# File 'lib/wavefile.rb', line 73

def self.open(path)
  file = File.open(path, "rb")
  
  begin
    header = read_header(file)
    errors = validate_header(header)

    if errors == []
      sample_data = read_sample_data(file,
                                     header[:num_channels],
                                     header[:bits_per_sample],
                                     header[:sub_chunk2_size])

      wave_file = self.new(header[:num_channels],
                           header[:sample_rate],
                           header[:bits_per_sample],
                           sample_data)
    else
      error_msg = "#{path} can't be opened, due to the following errors:\n"
      errors.each {|error| error_msg += "  * #{error}\n" }
      raise StandardError, error_msg
    end
  rescue EOFError
    raise StandardError, "An error occured while reading #{path}."
  ensure
    file.close()
  end
  
  return wave_file
end

Instance Method Details

#duration ⇒ Object 



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# File 'lib/wavefile.rb', line 246

def duration()
  total_samples = sample_data.length
  samples_per_millisecond = @sample_rate / 1000.0
  samples_per_second = @sample_rate
  samples_per_minute = samples_per_second * 60
  samples_per_hour = samples_per_minute * 60
  hours, minutes, seconds, milliseconds = 0, 0, 0, 0
  
  if(total_samples >= samples_per_hour)
    hours = total_samples / samples_per_hour
    total_samples -= samples_per_hour * hours
  end
  
  if(total_samples >= samples_per_minute)
    minutes = total_samples / samples_per_minute
    total_samples -= samples_per_minute * minutes
  end
  
  if(total_samples >= samples_per_second)
    seconds = total_samples / samples_per_second
    total_samples -= samples_per_second * seconds
  end
  
  milliseconds = (total_samples / samples_per_millisecond).floor
  
  return  { :hours => hours, :minutes => minutes, :seconds => seconds, :milliseconds => milliseconds }
end

#inspect ⇒ Object 



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# File 'lib/wavefile.rb', line 340

def inspect()
  duration = self.duration()
  
  result =  "Channels:        #{@num_channels}\n" +
            "Sample rate:     #{@sample_rate}\n" +
            "Bits per sample: #{@bits_per_sample}\n" +
            "Block align:     #{@block_align}\n" +
            "Byte rate:       #{@byte_rate}\n" +
            "Sample count:    #{@sample_data.length}\n" +
            "Duration:        #{duration[:hours]}h:#{duration[:minutes]}m:#{duration[:seconds]}s:#{duration[:milliseconds]}ms\n"
end

#mono? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/wavefile.rb', line 234

def mono?()
  return num_channels == 1
end

#normalized_sample_data ⇒ Object 



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# File 'lib/wavefile.rb', line 153

def normalized_sample_data()    
  if @bits_per_sample == 8
    min_value = 128.0
    max_value = 127.0
    midpoint = 128
  elsif @bits_per_sample == 16
    min_value = 32768.0
    max_value = 32767.0
    midpoint = 0
  else
    raise StandardError, "Bits per sample is #{@bits_per_samples}, only 8 or 16 are supported"
  end
  
  if mono?
    normalized_sample_data = @sample_data.map {|sample|
      sample -= midpoint
      if sample < 0
        sample.to_f / min_value
      else
        sample.to_f / max_value
      end
    }
  else
    normalized_sample_data = @sample_data.map {|sample|
      sample.map {|sub_sample|
        sub_sample -= midpoint
        if sub_sample < 0
          sub_sample.to_f / min_value
        else
          sub_sample.to_f / max_value
        end
      }
    }
  end
  
  return normalized_sample_data
end

#reverse ⇒ Object 



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# File 'lib/wavefile.rb', line 242

def reverse()
  sample_data.reverse!()
end

#sample_data ⇒ Object 



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# File 'lib/wavefile.rb', line 149

def sample_data()
  return @sample_data
end

#sample_data=(sample_data) ⇒ Object 



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# File 'lib/wavefile.rb', line 191

def sample_data=(sample_data)
  if sample_data.length > 0 && ((mono? && sample_data[0].class == Float) ||
                                (!mono? && sample_data[0][0].class == Float))
    if @bits_per_sample == 8
      # Samples in 8-bit wave files are stored as a unsigned byte
      # Effective values are 0 to 255, midpoint at 128
      min_value = 128.0
      max_value = 127.0
      midpoint = 128
    elsif @bits_per_sample == 16
      # Samples in 16-bit wave files are stored as a signed little-endian short
      # Effective values are -32768 to 32767, midpoint at 0
      min_value = 32768.0
      max_value = 32767.0
      midpoint = 0
    else
      raise StandardError, "Bits per sample is #{@bits_per_samples}, only 8 or 16 are supported"
    end
    
    if mono?
      @sample_data = sample_data.map {|sample|
        if(sample < 0.0)
          (sample * min_value).round + midpoint
        else
          (sample * max_value).round + midpoint
        end
      }
    else
      @sample_data = sample_data.map {|sample|
        sample.map {|sub_sample|
          if(sub_sample < 0.0)
            (sub_sample * min_value).round + midpoint
          else
            (sub_sample * max_value).round + midpoint
          end
        }
      }
    end
  else
    @sample_data = sample_data
  end
end

#save(path) ⇒ Object 



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# File 'lib/wavefile.rb', line 104

def save(path)
  # All numeric values should be saved in little-endian format

  sample_data_size = @sample_data.length * @num_channels * (@bits_per_sample / 8)

  # Write the header
  file_contents = CHUNK_ID
  file_contents += [HEADER_SIZE + sample_data_size].pack("V")
  file_contents += FORMAT
  file_contents += FORMAT_CHUNK_ID
  file_contents += [SUB_CHUNK1_SIZE].pack("V")
  file_contents += [PCM].pack("v")
  file_contents += [@num_channels].pack("v")
  file_contents += [@sample_rate].pack("V")
  file_contents += [@byte_rate].pack("V")
  file_contents += [@block_align].pack("v")
  file_contents += [@bits_per_sample].pack("v")
  file_contents += DATA_CHUNK_ID
  file_contents += [sample_data_size].pack("V")

  # Write the sample data
  if !mono?
    output_sample_data = []
    @sample_data.each{|sample|
      sample.each{|sub_sample|
        output_sample_data << sub_sample
      }
    }
  else
    output_sample_data = @sample_data
  end
  
  if @bits_per_sample == 8
    file_contents += output_sample_data.pack("C*")
  elsif @bits_per_sample == 16
    file_contents += output_sample_data.pack("s*")
  else
    raise StandardError, "Bits per sample is #{@bits_per_samples}, only 8 or 16 are supported"
  end

  file = File.open(path, "w")
  file.syswrite(file_contents)
  file.close
end

#stereo? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/wavefile.rb', line 238

def stereo?()
  return num_channels == 2
end