Hallo,

hier meine Lösung in Ruby. Aus den ursprünglichen 60 Zeilen sind nach etwas OOP-Refactoring jetzt doch noch 175 geworden.

Code ruby:
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#!/usr/bin/env ruby
require 'observer'
 
class Instrument
  attr_reader :data
 
  def initialize(pcm_data)
    @data = pcm_data
  end
 
  def sample_count
    @data.size
  end
 
  def sample(n)
    @data[n]
  end
 
  def self.from_file(path)
    File.open(path, 'rb') do |f|
      f.seek(44)
      data = f.read.unpack("s*")
      self.new(data)
    end
  end
end
 
 
class Note
  def initialize(instrument, velocity)
    @instrument = instrument
    @velocity = velocity
    @sample_num = -1
  end
 
  def next_sample!
    @sample_num += 1
    (@instrument.sample(@sample_num) * @velocity).to_i
  end
 
  def done?
    @sample_num >= @instrument.sample_count - 1
  end
end
 
 
class WaveWriter
  WAVE_HEADER = "\x52\x49\x46\x46%s\x57\x41\x56\x45\x66\x6d\x74\x20\x10\x00" +
                "\x00\x00\x01\x00\x01\x00\x44\xac\x00\x00\x88\x58\x01\x00\x02" +
                "\x00\x10\x00\x64\x61\x74\x61%s"
  WAVE_HEADER_SIZE = 44
 
  def initialize(io, sample_count)
    @io = io
    write_header(sample_count)
  end
 
  def <<(sample)
    @io.write [sample].pack("s")
  end
 
 private
  def write_header(sample_count)
    data_size = sample_count * 2
    header = WAVE_HEADER % [[data_size + WAVE_HEADER_SIZE - 8].pack("L"),
                            [data_size].pack("L")]
    @io.write header
  end
end
 
 
class Sequencer
  include Observable
 
  DEFAULT_RENDER_OPTIONS = {
    :beats_per_minute => 80,
    :ticks_per_beat   => 4,
    :sampling_rate    => 44_100.0,
  }
 
  def initialize
    @instruments = []
  end
 
  def add_instrument(instrument, roll)
    @instruments << [instrument, roll]
  end
 
  def render_wave(io, options = {})
    options = DEFAULT_RENDER_OPTIONS.merge(options)
    ticks_per_sec =
      options[:beats_per_minute] * options[:ticks_per_beat] / 60.0
    total_ticks = @instruments.map {|instrument, notes| notes.size}.max
    total_beats = (total_ticks.to_f / options[:ticks_per_beat]).ceil
    total_secs = total_beats.to_f / options[:beats_per_minute] * 60.0
    sample_count = (total_secs * options[:sampling_rate]).to_i
 
    wave = WaveWriter.new(io, sample_count)
 
    last_tick_num = -1
    notes = []
 
    sample_count.times do |sample_num|
      time = sample_num / options[:sampling_rate]
      tick_num = (ticks_per_sec * time).to_i
      if tick_num > last_tick_num
        last_tick_num = tick_num
        notes += notes_for_tick(tick_num)
        changed(true)
        notify_observers(tick_num.to_f / total_ticks)
      end
      notes.reject! {|note| note.done?}
      wave << mix_notes(notes)
    end
 
    changed(true)
    notify_observers(1.0)
  end
 
 private
  def notes_for_tick(tick_num)
    notes = []
    @instruments.each do |instrument, roll|
      symbol = roll[tick_num, 1]
      next if symbol.to_s.strip.empty?
      velocity = 0.5
      if symbol =~ /\d/
        velocity *= symbol.to_i * 0.1
      end
      notes << Note.new(instrument, velocity)
    end
    notes
  end
 
  def mix_notes(notes)
    notes.inject(0) {|result, note| result + note.next_sample!}
  end
end
 
 
if __FILE__ == $0
  DRUMKIT_DIR = "./drumkit"
 
  options = {
    :beats_per_minute => gets.to_i,
    :ticks_per_beat => gets.to_i
  }
 
  instruments = []
  while !(line = gets.strip).empty?
    instruments << File.join(DRUMKIT_DIR, line)
  end
 
  rolls = []
  while line = gets
    rolls << line
  end
 
  sequencer = Sequencer.new
 
  instruments.zip(rolls).each do |instrument, roll|
    sequencer.add_instrument(Instrument.from_file(instrument), roll)
  end
 
  $stderr.puts("Rendering...")
 
  progress_reporter = Object.new
  def progress_reporter.update(finished)
    $stderr.print("\r%d%%" % (finished*100))
  end
  sequencer.add_observer(progress_reporter)
 
  sequencer.render_wave($stdout, options)
end

Als Zugabe hier noch der Konverter, der Dateien im XML-Format von Hydrogen in unser Format umwandelt:
Code ruby:
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#!/usr/bin/env ruby
require 'rubygems'
require 'nokogiri'
 
doc = Nokogiri::XML(File.new(ARGV[0]))
instruments = []
doc.xpath("//instrumentList/instrument").each do |instrument|
  file = instrument.xpath("./layer/filename").first.text.sub(/\.flac$/, ".wav")
  instruments[(instrument/:id).text.to_i] = file
end
 
patterns = {}
size = 0
doc.xpath("//patternList/pattern").each do |pattern|
  name = (pattern/:name).text
  size = (pattern/:size).text.to_i
  roll = Array.new(instruments.size) {" "*size}
  pattern.xpath(".//note").each do |note|
    instrument = (note/:instrument).text.to_i
    position = (note/:position).text.to_i
    velocity = ((note/:velocity).text.to_f*10).to_i
    roll[instrument][position] = velocity.to_s
  end
  patterns[name] = roll
end
 
rolls = []
doc.xpath("//patternSequence/group/patternID").each do |pattern_id|
  $stderr.puts(pattern_id.text)
  rolls << patterns[pattern_id.text]
end
 
roll = rolls.transpose.map {|a| a.join}
 
puts doc.xpath("//song/bpm").text
puts size/4
instruments, roll = instruments.zip(roll).reject {|i,r| r.strip.empty?}.transpose
puts instruments
puts
puts roll

Grüße,
Matthias