Play a drone on the given note for five minutes

drone.rb

#!/usr/bin/env ruby

# drone.rb

# Take a note on the command line
# Play a drone on that note for LENGTH seconds or until stopped

# See https://muted.io/note-frequencies/
NOTES = {
  'G'  => 196.0,
  'G#' => 207.65,
  'Ab' => 207.65,
  'A'  => 220.0,
  'A#' => 233.08,
  'Bb' => 233.08,
  'B'  => 246.94,
  'C'  => 261.63,
  'C#' => 277.18,
  'Db' => 277.18,
  'D'  => 293.66 / 2,
  'D#' => 311.13 / 2,
  'Eb' => 311.13 / 2,
  'E'  => 329.63 / 2,
  'F'  => 349.23 / 2,
  'F#' => 369.99 / 2,
  'Gb' => 369.99 / 2
}

# Play drone for this many seconds
LENGTH = 300

usage = "Usage: drone.rb NOTE"
note = ARGV[0]

if !note
  puts usage
  exit 1
end

# Allow note to be entered in lower case
note = note.capitalize

if !NOTES.has_key?(note)
  puts usage
  exit 1
end

puts "Note #{note} is #{NOTES[note]}Hz"
puts "Ctrl-C to stop"

# Use Sox
#`play -n synth #{LENGTH} sin #{NOTES[note]}`

# Use ffplay
`ffplay -f lavfi -i "sine=frequency=#{NOTES[note]}:duration=#{LENGTH}" -autoexit -nodisp 2>/dev/null`