Digital Effects

Audio Effects

  • Take an input sound, output a modified version

  • All the commercial audio you hear is heavily effects processed: unprocessed "sounds bad" to a modern ear

  • Artistic effects blend into engineering: things like limiting amplitude and bandwidth, correcting phase, limiting noise, etc are necessary in the audio chain but also can sound cool

  • Example: Autotuner. Originally for correcting vocalist pitch issues, now also used as an artistic effect

Effects Challenges

  • Often "realtime" effects

    • Must have adequate throughput

    • Latency can be a big deal, especially in chains of effects

    • (Realtime effects can be used "offline" too)

  • Often run on really simple hardware: traditionally analog, now tiny microcontrollers

  • Complexity of effects chains can be high: "enough knobs, but not too many"

  • Lots of emulation effects: modeling something else is hard

    • e.g. microphones, amplifiers / speaker cabinets

    • e.g. room effects, telephone effects

Effects Chains

  • Often want to apply multiple effects

  • Build DAG for signal processing

    • Splitting is easy in digital

    • Still need to specify mixing for combining signals

    • Challenges: multichannel, latency matching

Effects Control and Configuration

  • So many different knobs, displays etc

  • Want to save / restore complex effects chain config

  • Want to have "metaknobs": simplified control for entire effects chain

  • Next lecture: plugins and effects "racks"

  • Lots of open questions here

Example: Compression/Expansion

  • Idea: Compression — try to hold output volume level more steady as function of input volume

  • Idea: Expansion — try to make changes in input volume more pronounced on output

  • Typical implementation: two different linear (in log space because volume) gain functions with a "knee"

  • Switching functions at knee must not be instantaneous, else signal will distort: "attack" time to move to upper curve, "decay" time to move back to lower curve

  • Used a lot because "professional sound" and because always-high volume is desirable

  • Demo: http://github.com/pdx-cs-sound/compressor

Last modified: Sunday, 26 April 2020, 11:14 PM