Generate sample chains for use with the Elektron Octatrack

sample-chain

#!/usr/bin/env ruby
require 'pathname'

def run_cmd(*cmd)
  io = IO.popen cmd.map(&:to_s)
  io.read.chomp
end

class Sample
  include Comparable

  attr_reader :filename, :duration, :sample_rate

  def initialize(filename)
    @filename    = filename
    @sample_rate = (run_cmd 'soxi', '-r', filename).to_i
    @duration    = (run_cmd 'soxi', '-s', filename).to_i
  end

  def pad(max_duration)
    diff = (max_duration - duration) / sample_rate.to_f
    run_cmd 'sox', filename, padded_filename, 'pad', 0, diff
  end

  def padded_filename
    @padded_filename ||= filename.sub(/.wav$/, '.padded.wav')
  end

  def <=>(rhs)
    duration <=> rhs.duration
  end
end

class SampleChain
  attr_reader :samples

  def initialize(input)
    @samples = begin
      input.map { |x| Pathname.new(x) }
           .select(&:exist?)
           .map { |x| Sample.new(x.to_s) }
    end
  end

  def save_to(output)
    # Pad samples
    samples.each { |x| x.pad(longest_sample.duration) }

    # Concatenate padded files
    run_cmd 'sox', *padded_samples, output

    # Clean up padded files
    run_cmd 'rm', '-f', *padded_samples
  end

  private

  def longest_sample
    @longest_sample ||= samples.max
  end

  def padded_samples
    @padded_samples ||= samples.map(&:padded_filename)
  end
end


# Get input from arguments or read from stdin
input = (ARGV.empty? ? $stdin.read.split : ARGV)

SampleChain.new(input).save_to('out.wav')