Audacity

http://audacity.sourceforge.net/

Matt Brubeck

What is Audacity

Free (GPL) sound editor for Linux, Mac OS X, and Windows

What does it do?

• Recording and playback
• Multi-track recording and mixing
• Editing (cut, copy, paste, ...)
• Effects (reverb, change pitch, noise removal, ...)
• Analysis (spectrograms, frequency analysis)

Demonstration

Who uses Audacity?

• Everybody!
• Amateur musicians
• Community radio stations
• Audiobloggers
• Vinyl and cassette owners

Cross-Platform

Windows

Mac OS X

• Uses cross-platform wxWidgets and PortAudio APIs.

Cross-Platform

Features

• High-quality audio I/O: 32 bits / 96 KHz
• Transparent resampling and dithering
• Unlimited number of tracks
• Full duplex recording
• Fast editing with unlimited undo

Development

• Created in 1999 by Dominic Mazzoni at CMU
• 2-3 core maintainers, 4-6 active developers, dozens of contributors

Development

• Based on:
  • wxWidgets
  • Portaudio
  • libsndfile
• Optionally uses:
  • MAD
  • libogg/libvorbis
  • libresample
  • soundtouch
  • Nyquist
  • expat

Data Structures

Traditional audio data structures:

• Keep all data in memory
  • Scales poorly
• Apply changes directly to disk
  • Destructive, slow
• Edit Decision List
  • Used by most non-destructive editors

Audacity's data structure

• Divide each track into 1–2 MB "blockfiles".
• Blockfiles are immutable
• Each blockfile may be referenced more than once
• Allows non-destructive editing, fast insertion & deletion

Audacity's data structure

Plug-ins

• LADSPA
• VST (Using optional VST-LADSPA bridge)
• Nyquist

Nyquist

;nyquist plug-in
;version 1
;type process
;name "Tremolo..."
;action "Applying Tremolo..."
;control amount "Wetness"   int  "%"  40  0   100
;control lfo    "Frequency" real "Hz" 4.0 0.1 10.0

(mult (sum (const (- 1.0 (/ amount 200.0))) 
      (scale (/ amount 200.0) 
             (osc (hz-to-step lfo)))) s)

Legal issues

• MP3 patents
• VST SDK license
• "Audacity" trademark
• eBay vendors

Recent development

Audacity 1.2.2

• Level meters
• Latency correction

Audacity 1.3 (unstable)

• New label tracks
• Multiple clips per track

Any questions?