YUP Audio Plugin Review

YUP looks JUCE-like in places, but its plugin API has its own parameter handles, bus layout, editor contract, and wrapper behavior. Review those directly instead of applying APVTS rules.

Step 0 - Run universal checks first

Invoke audio-dsp-review and audio-numerics-review before this skill. This skill adds YUP-specific checks on top; it does not replace realtime-safety or numerics reviews.

Step 1 - Identify plugin structure

Locate the core classes and boundaries:

• yup::AudioProcessor - audio thread owns processBlock; wrapper/host code calls lifecycle, state, and preset methods
• yup::AudioProcessorEditor - UI/message thread only; never call from audio thread
• yup::AudioParameter - atomic scalar value plus listeners for host/UI notification
• yup::AudioParameterHandle - audio-thread smoothing/read path; initialise in prepareToPlay
• yup::AudioBusLayout - immutable I/O contract exposed to plugin wrappers
• extern "C" yup::AudioProcessor* createPluginProcessor() - plugin entry point used by wrappers

Step 2 - Scan for YUP violations

Violation	Where to look	Risk
AudioParameterHandle default-constructed and used before prepareToPlay	Members and processBlock	Null parameter assertion/crash; wrong smoothing state
Missing handle.updateNextAudioBlock()	processBlock	Automation and smoothing lag or never update
Recreating AudioParameterHandle in processBlock	Audio callback	Reinitialises smoothing and may add avoidable work/glitches
setValueNotifyingHost(), beginChangeGesture(), or endChangeGesture() from audio code	processBlock, MIDI handlers, DSP helpers	Listener/host notification path is not a realtime data path
Allocating voices, buffers, MemoryBlock, String, std::vector, or smart-pointer objects in processBlock	MIDI note-on, scratch buffers, metering	Heap traffic causes xruns
YUP_DBG, Logger::writeToLog, File, URL, JSON/XML, or string formatting in audio code	Debug and error paths	Logging/I/O/allocation on audio thread
Hard-coded channel pointers without layout checks	getWritePointer(0/1) and bus setup	Mono, sidechain, or unusual host layout crashes/corrupts audio
Mutating MidiBuffer while iterating it	MIDI loops	Iterator invalidation or unbounded allocation
prepareToPlay not resetting all DSP and note state	Lifecycle methods	Host reactivation leaves stale filter history, held notes, or ramps
flush() missing for synths/effects with tails or voices	CLAP reset handling	Host reset leaves hanging notes or stale delay/reverb tails
State load/save left unimplemented	loadStateFromMemory, saveStateIntoMemory	DAW session recall and presets fail
Long work under getProcessLock() or state swaps with no handoff	UI/state/background code	Processing may skip under CLAP try-lock or race under other wrappers
Editor stores raw processor-owned UI pointers or processor stores editor pointer	Editor/processor members	Dangling pointer when host closes editor

Step 3 - Check YUP API contracts

• Constructor: parameters are added once; IDs are unique and stable; bus layout matches PLUGIN_IS_SYNTH / PLUGIN_IS_MONO intent.
• prepareToPlay: allocates and resets all state; constructs handles with current sample rate; tolerates repeated calls.
• processBlock: reads smoothed parameters through handles; respects audioBuffer.getNumSamples() and actual channel count; clears or writes every output sample it owns.
• MIDI: consumes events in sample order; uses bounded voice/event storage; clears or rewrites outgoing MIDI deliberately.
• Editor: uses gesture begin/end around drags; calls setValueNotifyingHost() for user changes; polls parameter values with a timer using dontSendNotification.
• State/presets: serialises all host-visible parameters and preset data; validates memory before applying; does not assume state callbacks are the audio thread.
• Format wrappers: CLAP and VST3 builds are enabled only as needed; CLAP/VST3/standalone targets all link the same ${target_name}_shared code.

Step 4 - Write the review

## YUP Plugin Review: `[file / class]`

### Verdict
[Safe | Has critical violations | Warnings only] - [one sentence summary]

### Critical Violations
**[Category]: [description]**
`file:line` - `offending code`
Why: [one sentence on YUP lifecycle/thread/API risk]
Fix: [concrete YUP-idiomatic suggestion]

### Warnings
[same format]

### What's Done Well
[correct patterns observed]

### Recommended Fixes (priority order)
1. ...

Quick fix table

Violation	Fix
Direct unsmoothed parameter read for DSP	Keep AudioParameter::Ptr, initialise AudioParameterHandle in prepareToPlay, read via the handle
Missing gesture pairing	Call beginChangeGesture() on drag start and endChangeGesture() on drag end
UI value changes with setValue()	Use setValueNotifyingHost() for user edits so automation/host state is notified
Allocating voices on note-on	Preallocate voice slots and reuse them; reject/steal voices when full
Hard-coded stereo	Declare stereo in AudioBusLayout and guard getNumChannels() before channel access
Missing reset	Clear voices, delay lines, filters, smoothers, and pending MIDI in both prepareToPlay and flush() where relevant
Unimplemented state recall	Serialise parameters and presets into MemoryBlock; validate and apply from non-audio state callbacks
Audio-to-UI updates	Write scalars to atomics or a preallocated lock-free queue; have editor Timer poll them

For full code examples and YUP-specific BAD/GOOD patterns, see references/yup-violations.md.