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