Road to RubyKaigi: Making Tinny Chiptunes with Ruby

Road to RubyKaigi: Making Tinny Chiptunes with Ruby
2025.04.17. RubyKaigi 2025 LT

1. Road to RubyKaigi: Making Tinny Chiptunes with Ruby @makicamel RubyKaigi 2025 2025.04.17
2. Self Introduction @makicamel / Maki Kawahara Loves Ruby , beer , and alcoholic drinks AndPad Inc. Creater of "Road to RubyKaigi"
3. Road to RubyKaigi 　　Road to RubyKaigi 　https://github.com/makicamel/road_to_rubykaigi
4. Road to RubyKaigi A Ruby-made game by Rubyist for Rubyists A side-scrolling action game played in the terminal Defeat bugs and escape deadlines to reach RubyKaigi venue `gem install road_to_rubykaigi`
5. Road to RubyKaigi Gameplay Video
6. Road to RubyKaigi Something is missing... Music!
7. Music with Ruby is Hot 4 sound tracks!
8. Music macOS does not have a built-in active sound source by default The user must adjust system settings Inconvenient
9. A Haiku Here
10. A Haiku Here
11. Making Music Sound is a wave
12. Making Music A sound source creates the waves Ruby is the sound source
13. Making Music Devices that output the created wave Audio devices e.g. Speakers, Headphones
14. Making Music Audio device I/O APIs macOS Core Audio Windows Windows Audio Session API Linux Advanced Linux Sound Architecture
15. Making Music A cross-platform library that provides audio I/O APIs PortAudio https://github.com/PortAudio/portaudio The Ruby binding for PortAudio ffi-portaudio https://github.com/nanki/ffi-portaudio
16. Making Music Create a wave (audio data) 1. Pass it to ffi-portaudio Output it through PortAudio to an audio device 2. Play sound with Ruby! 3.
18. Basics of Creating Waves "Sound is a wave" What does it mean?
19. Basics of Creating Waves Representative waveforms Sine wave Square wave Triangle wave Sawtooth wave 　　Square wave (waveform) 　https://en.wikipedia.org/wiki/Square_wave_(waveform)
20. Basics of Creating Waves Periodic The changes in signal amplitude follow a repeating pattern Frequency Number of cycles per second e.g. 444.0Hz Repeat 440 cycles per second 　　Square wave (waveform) 　https://en.wikipedia.org/wiki/Square_wave_(waveform)
21. Basics of Creating Waves Period The time it takes for one cycle 　　Square wave (waveform) 　https://en.wikipedia.org/wiki/Square_wave_(waveform)
22. Basics of Creating Waves Analog The amplitude of a wave changes continuously within a cycle Digital A continuous signal amplitude cannot be recorded Instead, record so that it appears continuous a fixed number of samples This number is "sample rate" Sample rate The number of samples per second
23. Basics of Creating Waves How to generate waves Just collect the changes in the signal and repeat them
25. Practical Approach to Creating Waves Generate the "pico-pico" sound like the NES The waveforms generated by the NES Square wave Triangle wave In this talk, we focus on square waves
26. Creating Waves: Square Wave Only two values 1 and -1 The typical "pico-pico" sound
27. Creating Waves: Square Wave The first half of a cycle is 1 The second half is -1
28. Creating Waves: Square Wave Frequency The number of cycles per second Time per sample: 1 second / sample rate Increment in current phase per sample: frequency / sample rate class SquareOscillator def tick(frequency:) @phase += frequency.to_f / sample_rate @phase -= 1.0 if @phase >= 1.0 # Phase is managed from 0 to 1, reset when reaching 1 @phase end
29. Creating Waves: Square Wave Waveform generation class SquareOscillator # ... def generate(frequency:) # Get the current phase within the cycle phase = tick(frequency: frequency) # 1 if in the first half, -1 if in the second half phase < 0.5 ? 1.0 : -1.0 end end Collecting samples produces a square wave
30. Creating Waves: Square Wave Passing to PortAudio class AudioEngine < FFI::PortAudio::Stream def process(_input, output, framesPerBuffer, _timeInfo, _statusFlags, _userData) samples = (0...framesPerBuffer).map { @oscillator.generate(frequency:) } output.write_array_of_float(samples) :paContinue end # ... The sound plays!
31. Creating Waves: Square Wave Waveform output from the audio device
32. Creating Waves: Square Wave Waveform output from the audio device
33. Creating Waves: Square Wave
34. Creating Waves Advanced Changing the signal strength abruptly generates noise Many high-frequency components are produced Digital-to-analog conversion
35. Creating Waves Advanced Noise reduction Smoothing the corners 　　To reduce noise caused by abrupt signal changes, a filter is effective 　　but since we want "pico-pico" sound, not adopt in this talk
36. Creating Waves Advanced When the current position in the cycle is at a sharp corner add offset to the signal's strength
37. Creating Waves Advanced When the current position in the cycle is at a sharp corner add offset to the signal's strength Use the cosine function to draw curves like
38. Creating Waves Advanced The waveform becomes clean
39. Making Music Then, write scores
40. Making Music Several combinations Triangle wave Pseudo triangle wave Envelopes Sound effects
41. Making Music Simply pass it to the API class AudioEngine < FFI::PortAudio::Stream def process(_input, output, framesPerBuffer, _timeInfo, _statusFlags, _userData) samples = (0...framesPerBuffer).map { @oscillator.generate(frequency:) } output.write_array_of_float(samples) :paContinue end # ...
42. Demo
43. Special Thanks @youchan
44. Enjoy Creating!