Linux ProAudio

title

Linux Pro Audio

author

Alexander Patrakov

JACK

• JACK Audio Connection Kit
• Connects Pro Audio applications with each other and with sound card
• Two implementations exist: jackd1 and jackd2

Types of Pro Audio applications

• Digital audio workstations
• Loopers
• Sequencers
• Synths
• Effect racks
• Programming environments
• Others

This slideshow will be mostly about programming environments

• CSound
• Pure Data (Pd)
• Faust

Audio data types

• Sampled audio
  • Usually recorded from a microphone, but may be synthesized
  • That's what the consumer gets
• MIDI
  • Musical Instrument Digital Interface
  • Conveys information about musical notes
    • Notation, pitch, velocity, volume, panning, etc.
    • Also has control messages
• OSC
  • Open Sound Control
  • Protocol for networking sound synthesizers, computers, and other multimedia devices for purposes such as musical performance or show control
  • Think of it as a next-generation networked MIDI

CSound

• Created in 1985 by Barry Vercoe
• A command-line tool
• Takes two text files as input
  • Orchestra (set of instruments - descriptions how to make sounds)
  • Score (description of what instruments to use, when and how)
  • Those two may be unified into a single CSD file
• Produces a wave file as an output
• Can also interface with audio and MIDI hardware

Mechanism

• Orchestra contains instrument definitions
• Instrument definitions contain calls to opcodes
• Opcodes update variables
  • a-, k-, i- variables are available
  • a- = updated at audio rate, k- = at control rate, i- = at initialization only
• Finally, some of the variables are sent to the instrument output

Available primitives (opcodes) for instruments

• ~1500 opcodes are built-in
  • Simple math
  • Oscillators
  • Additive, subtractive, FM and other synthesizers
  • Filters
  • Envelope generators
  • Ways to define new opcodes in terms of existing ones
• User who knows C can also extend CSound with new opcodes

CSound ecosystem

• CSound itself
• Editors that make editing instrument definitions and scores easy
• Journals and user forums
• Showcases on soundcloud and elsewhere