DSP Implementation Notes

This page explains what each DSP family does internally.

It complements three reference pages:

Page	Role
Mastering Processors	Public processor registry
Algorithm References	Standards, algorithm names, and compatibility references
Implementation Validation	Feature groups mapped to tests

Use this page when you need implementation context before exposing a processor in a UI, choosing real-time settings, or explaining a render report.

The source of truth is the C++ implementation in the libsonare repository.

Area	Source
DSP implementation	src/analysis, src/feature, src/mastering, src/effects, src/mixing, src/engine
Public mastering processor names	src/mastering/api/named_processor_registry.cpp
Analysis and feature helpers	Quick APIs and language bindings

Reading this for the first time

This page is implementation-oriented, so there is no need to absorb all of it at once. Start from the idea that DSP is the umbrella term for treating audio as a sequence of numbers and measuring, separating, or transforming it. Read the "Main use" column of each table and go deeper only on the processors you will actually use.

If you only want a BPM, read Analysis And Feature DSP; if you are finishing a track for loudness or delivery, read Mastering Chain and Final Stage and Maximizers.

Which Processor For Which Job

Goal	Start with
Reach a loudness target	The chain's loudness slot, or maximizer.loudnessOptimize for a whole file; see Final Stage and Maximizers
Keep peaks under a ceiling	maximizer.truePeakLimiter or dynamics.brickwallLimiter
Even out dynamics	Dynamics
Shape tone	EQ and Spectral and Stereo
Remove noise, hum, clicks or clipping	Repair
Add space or movement	Effects and Editing DSP and Modulation, Delay, Filter and Utility Inserts
Widen, narrow or check the stereo image	Spectral and Stereo
Match a reference	Reference Matching and Analysis
Get a BPM, key or chords	Analysis And Feature DSP

What You Will Learn

By the end of this page you should be able to:

• identify the shared DSP building blocks behind analysis, effects, mastering, mixing, and realtime processing;
• explain the difference between public processor names and the lower-level implementation pieces that realize them;
• spot realtime-sensitive implementation details such as lookahead, allocation, FIR rebuilds, smoothing, and latency;
• know which source directories to inspect when behavior needs to be verified.

Reading Path

Need	Page
Public processor IDs and preset names	Mastering Processors
DSP behavior, shared building blocks, and real-time boundaries	This page
Standards, papers, and compatibility references	Algorithm References
Test coverage and validation status	Implementation Validation

Shared Building Blocks

Most processors are not built from unique magic. They combine a small set of parts — filters, level detection, delay, stereo transforms, convolution — and the table below shows where each part turns up.

Building block	Implementation role	Used by
Biquad and filter design	Low-latency IIR EQ, shelves, cuts, presence/air shaping, detector filtering	EQ, dynamics sidechains, spectral enhancers, stereo filters
Envelope follower	Attack/release smoothing for level detectors and gain changes; each time is one time constant, about 63% of the way at the set time	Compressors, expanders, gates, de-esser, vocal rider, limiters
Parameter smoother	Click-free parameter transitions in block processing; a glide settles exactly on its target at every sample rate, and an interrupted glide continues from the value already applied	Mastering processors, mixer strip controls, automation
Lookahead and sliding maximum	Future-aware peak control without overshoot	Brickwall limiter, true-peak limiter, maximizers
Oversampling and true-peak filter	Inter-sample peak estimation and anti-aliasing headroom	Limiters, clippers, saturation, final output
Delay lines	Time alignment, Haas widening, modulation delay, ducking alignment	Stereo, delay, modulation, mixing alignment
Mid/side transform	Independent mono center and stereo side processing	Mid/side EQ, imager, mono maker, stereo balance
Partitioned convolution	Efficient block convolution for long kernels or impulse responses	Convolution reverb, linear-phase EQ, match EQ
Noise tracker and LPC helpers	Classical noise profile tracking and LPC residual/reconstruction helpers	Denoise uses NoiseTracker; declick/declip use LPC helpers

Plain-language gloss of the building blocks

• Lookahead — the processor delays the audio slightly so it can "see" a peak a few milliseconds before it plays, and turn the gain down smoothly instead of clamping it. The cost is a little latency.
• True-peak interpolation — uses an oversampled reconstruction filter to estimate peaks between stored samples. It approximates the specified reconstruction response; it does not measure a particular DAC's analogue output.
• Oversampled nonlinear processing — runs a distortion-producing processor at a higher rate, then filters before returning to the original rate to reduce audible aliasing. This is a separate use of oversampling from true-peak metering.
• Mid/side (M/S) — re-expresses a stereo signal as a mid (mono center) channel and a side (left-minus-right difference) channel, so you can process the center and the width independently, then convert back.
• Partitioned convolution — convolution applies one signal's "fingerprint" to another (e.g. a room impulse response, or a linear-phase EQ). Partitioning splits a long filter into blocks so it can run efficiently in real time.
• Haas widening — a very short delay (under ~40 ms) on one channel that the ear hears as extra stereo width rather than an echo.
• LPC (linear predictive coding) — models a sample as a prediction from the samples before it; repair uses it to reconstruct what a clicked or clipped peak should have been.

Analysis And Feature DSP

The analysis side — music information retrieval (MIR): extracting tempo, key, chords, and similar musical facts from audio — is built from reusable feature stages rather than one monolithic analyzer. STFT (short-time Fourier transform) and frame utilities feed mel/MFCC, chroma, onset envelopes, tempograms, and section features. YIN-style pitch tracking works from waveform periodicity; its FFT-accelerated difference calculation is separate from the cached STFT spectrogram. Higher-level analyzers reuse representations where possible.

For a newcomer, the analysis side runs roughly like this:

1. Cut the audio into short windows.
2. Compute the representation the task needs: a spectrum for spectral features, or a periodicity measure for F0 tracking.
3. Build a purpose-specific summary: onsets for rhythm, chroma for harmony, mel or MFCC for timbre, or a pitch contour for melody.
4. Estimate the high-level result — BPM, key, chords — from those summaries.

Family	Implementation role	Main use
STFT and framing	Windowed FFT over overlapping frames, with shared frame/hop conventions	Foundation for spectral, chroma, onset, mel, and MFCC features
Mel / MFCC	Mel filterbank plus DCT-style cepstral compression, with optional cepstral liftering (lifter, default 0 = off)	ML features, timbre summaries, librosa-compatible workflows
Chroma / CQT / VQT / NNLS chroma	Pitch-class and log-frequency representations, including a constant-Q chromagram (chromaCqt)	Key, chord, harmonic similarity, and pitch-aware features
Onset / tempogram / PLP	Onset envelope and local periodicity representations	BPM, beat, rhythm, and pulse analysis
Pitch tracking	YIN and pYIN style F0 estimation	Melody extraction and monophonic pitch analysis
Inverse features	NNLS (non-negative least squares) mel-filterbank inversion, inverse-DCT MFCC un-projection, and Griffin-Lim audio synthesis	Debug previews and feature round-trip checks
Room acoustics	Energy decay curve metrics for IRs, blind free-decay fitting, equivalent-room estimation, image-source RIR synthesis, and creative room morphing	RT60, EDT, C50, C80, D50, band decay, volume, dimensions, absorption, DRR, generated RIRs, and confidence

Feature inversion, blind acoustic estimation, and equivalent-room estimation are useful, but they are estimates. Inverse helpers cannot restore discarded phase or mel/MFCC detail; blind acoustic and room-estimation modes report confidence because ordinary recordings may not contain a clean free-decay region.

Mastering Chain

masteringChain(...) builds a fixed processor chain from a structured configuration: the same configuration and input always produce the same stage order and the same output, with no run-to-run variation. That is what "deterministic" means here.

The streaming variant, StreamingMasteringChain, runs the same stages in the same order, but it keeps each processor's state between audio blocks so it can run live.

Offline-only processors can still appear in high-level workflows. Real-time render paths are limited by each processor's contract; changes that resize buffers or rebuild FIR kernels are not audio-thread safe.

Presets are not separate DSP algorithms. They are named configurations that enable selected repair, EQ, dynamics, saturation, spectral, stereo, maximizer, and loudness slots with genre/platform defaults.

The fixed slot order is repair → EQ → dynamics → saturation → spectral → stereo (stereo path only) → maximizer → loudness. A configuration can skip a slot, but cannot reorder it. The full chain figure shows every slot and which ones a sample preset enables. The loudness slot includes its own true-peak limiter after normalization; presets avoid enabling a separate maximizer limiter as well, which would limit twice. Its gain is solved by remeasuring the signal at the candidate gain, so it lands on the gated loudness target even when the gain moves blocks across the absolute gate; the streaming chain takes the same gain from streamingLoudnessGain.

Every insert reports a latency and a tail. The tail is the number of samples the output keeps ringing after the input stops, counted down to 1e-5 of full scale, and it covers IIR EQs, filters, saturation, stereo inserts, modulated delays, oversampled stages, and multiband crossovers as well as reverbs; bounce and freeze lengths are sized from it. A stage switched off and back on starts from rest instead of replaying the history it held, and set_config rebuilds only the stage whose field changed, leaving the processor as it was when a configuration is refused.

Dynamics

Processor	Implementation	Main use	Real-time notes
dynamics.brickwallLimiter	Lookahead peak detector with fast gain reduction and ceiling enforcement	Prevent sample peaks from exceeding a ceiling	Adds lookahead latency; safe when prepared before streaming
dynamics.compressor	Feed-forward level detector, attack/release envelope, ratio/knee gain computer, makeup gain	Control macro dynamics and make a master feel more cohesive	Smooth parameter changes to avoid gain zipper noise
dynamics.deesser	Split-band de-esser with band-pass filters, threshold, ratio, attack/release, range, and bandpass Q	Attenuate sibilant high-frequency energy	Listed parameters are automatable without allocation or state reset
dynamics.expander	Downward expansion below a threshold using envelope detection	Increase contrast and reduce low-level spill	Release time dominates audibility
dynamics.gate	Threshold gate with hysteresis-style open/close behavior	Suppress background noise between events	Hold/release settings avoid chatter
dynamics.limiter	Peak-oriented compressor with high ratio and short timing	Catch short transients before final output	Lower latency than lookahead brickwall limiting, less absolute
dynamics.parallelComp	Compressed path blended with dry path	Add density while preserving transients	A shared combiner aligns every parallel path to the longest delay and reports it, so the blend stays phase-aligned
dynamics.sidechainRouter	Routes an external or derived control signal into a dynamics detector	Sidechain-dependent compression or ducking	Primarily an internal routing helper exposed for advanced graphs
dynamics.duckingProcessor	Sidechain envelope lowers the program path when the key signal is active	Voice-over music ducking and broadcast-style mixes	Attack/release shape determines speech intelligibility
dynamics.transientShaper	Separates attack and sustain envelopes and applies independent gain	Emphasize or soften hits	Fast detector path is sensitive to block size; reports its gain reduction
dynamics.upwardCompressor	Raises material below a threshold instead of pushing loud material down	Increase detail and perceived density	Can raise noise floor; pair with denoise or gating when needed
dynamics.upwardExpander	Lifts material above a lower threshold while leaving the quietest portions untouched	Restore articulation without hard gating	More musical than a gate for ambience-heavy sources
dynamics.vocalRider	Slow envelope follower adjusts vocal level toward a target range	Automatic level riding for vocals or speech	Designed as gradual gain automation, not a peak limiter; reports its gain reduction

Dynamics terms: knee, makeup gain, sidechain, ducking

• Knee — the shape of the input/output curve around the threshold. A hard knee changes slope at the threshold; a soft knee blends into the compressed slope over a range. Attack and release determine how quickly the gain follows that curve.
• Makeup gain — after a compressor lowers the loud parts, the whole signal is quieter, so makeup gain raises it back up to a comparable level — now more even than before.
• Sidechain — feeding a different signal into a processor's level detector so it reacts to that signal instead of itself.
• Ducking — the classic sidechain use: a music bed automatically dips whenever a voice (the key signal) is present, then comes back up when the voice stops.
• Brickwall limiter — a limiter with such a high ratio and fast response that nothing is allowed past the ceiling at all, as if hitting a wall.

EQ

Processor	Implementation	Main use	Real-time notes
eq.bandPass	Biquad band-pass filter	Isolate a frequency region	Low latency
eq.cutFilter	High-pass/low-pass cut filters with slope control	Remove rumble, hiss, or band-limit a signal	Low latency IIR path
eq.dynamic	EQ band controlled by an envelope detector	Frequency-selective compression/expansion	Detector timing must be smoothed
eq.equalizer	Multi-band EQ engine with validation, routing, and spectrum helpers	General corrective and tonal EQ	IIR path is live-friendly
eq.graphic	Fixed-band graphic EQ	Broad tonal shaping with predictable bands	Low latency
eq.linearPhase	FIR/linear-phase style EQ path	Phase-preserving mastering moves	Adds latency and is better suited to offline or latency-aware streaming
eq.midSide	Converts L/R to M/S, applies EQ independently, converts back	Shape center and width bands separately	Needs stereo input and careful mono compatibility checks
eq.minimumPhase	Minimum-phase EQ topology	Mastering EQ where low latency matters	Preferred for live paths
eq.parametric	Parametric peak/shelf/cut bands	Precise corrective EQ	Low latency
eq.passiveTube	Passive-style program equalizer with low boost, low attenuation, high boost, high attenuation, component model, and output drive controls	Low/high program EQ shaping	Most controls are marked automatable; component model is not automatable
eq.shelving	Low/high shelf filters	Tilt lows or highs around a corner frequency	Low latency
eq.steppedProportionalQ	Four-band stepped proportional-Q biquad EQ	Tonal shaping with stepped frequency/gain controls	In-place coefficient changes; gain snaps in 2 dB steps; Q narrows with larger gain magnitude
eq.tilt	Complementary low/high shelving around a pivot	Quick bright/dark tonal balance	Useful in presets and assistant suggestions

Final Stage and Maximizers

Processor	Implementation	Main use	Real-time notes
final.bitDepth	Quantizes samples to a target bit depth	Preview or export bit-depth reduction	Usually last or near-last
final.dither	Adds shaped or unshaped low-level noise before quantization	Reduce quantization distortion	Export-stage processor
final.outputChain	Groups output gain, ceiling, bit depth, dither, and final checks	Last-stage export preparation	Keep after tonal/dynamics stages
maximizer.adaptiveRelease	Limiter release time adapts to signal behavior	Cleaner loudness increase with fewer pumping artifacts	Adds detector state; reports 129 samples of latency at its defaults
maximizer.loudnessOptimize	Measures loudness and applies gain strategy toward a target	Hit LUFS (loudness units relative to full scale) targets for streaming/broadcast	Full-file optimization is offline by nature
maximizer.maximizer	Loudness-oriented limiting with ceiling management	Raise perceived loudness	Use true-peak stage after aggressive settings
maximizer.softKneeMax	Soft-knee limiting curve before hard ceiling	Less abrupt limiting	Useful before final true-peak protection
maximizer.truePeakLimiter	Oversampled true-peak estimation and ceiling control; an output guard rechecks every earlier position a correction can raise, so short bursts hold the ceiling	Avoid inter-sample overs	Adds oversampling cost and lookahead-style latency (129 samples at the defaults); lowering the ceiling live re-evaluates output already queued

METERS · LOUDNESSIDLE

Loudness metering — LUFS, true-peak, and range

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The bar tracks momentary loudness as the clip plays; the panel is the loudness over time. Integrated LUFS is the single overall number, true-peak estimates peaks between samples, and LRA captures how much the loudness moves. Switch the window to compare the fast momentary meter with the smoother short-term one — each reports only once its window has filled, so the short-term contour starts three seconds into the clip.

Window

Multiband

Processor	Implementation	Main use	Real-time notes
multiband.compressor	Crossover splits bands, each band runs compression, bands sum back	Frequency-dependent dynamics control	Crossover design and latency compensation matter
multiband.dynamicEq	Dynamic EQ behavior applied across band regions; a band switched back on restarts its detector, EQ slot, and gain glide from rest	Control resonant or harsh ranges only when active	Detector smoothing is essential
multiband.expander	Per-band expansion below thresholds	Clean low-level noise or restore contrast by band	Can change tonal balance if overused
multiband.imager	Per-band stereo width/mid-side processing	Keep lows mono while widening upper bands	Always check mono compatibility
multiband.limiter	Per-band limiting before recombination; bands with different lookahead or oversampling are time-aligned	Catch band-specific peaks	Avoid excessive crossover artifacts
multiband.saturation	Per-band nonlinear drive and blend	Add harmonic color by range	Oversampling or conservative drive reduces aliasing

Repair

Processor	Implementation	Main use	Real-time notes
repair.declick	Detects isolated impulse-like discontinuities and interpolates or attenuates them	Remove clicks and small digital defects	Detection window introduces local lookaround
repair.declip	Estimates clipped regions and reconstructs peaks	Repair hard-clipped audio	Offline-friendly because reconstruction uses context
repair.decrackle	Tracks dense small impulses and smooths them	Reduce vinyl-like crackle	More expensive than single-click removal; causal, also a realtime insert (median mode)
repair.dehum	Notch-style suppression of hum fundamentals and harmonics	Remove mains hum	Low latency when configured frequencies are known; also a realtime insert
repair.denoiseClassical	Noise tracking and spectral attenuation	Reduce stationary background noise	Profile estimation is context-dependent; also a realtime insert, delayed by its reported latency, with a streaming noise estimator (spp by default)
repair.dereverbClassical	STFT-domain dereverb configuration with t60_sec, late_delay_ms, over-subtraction, spectral floor, and optional WPE settings	Reduce room tail and smear	File-level API returns a new Audio object; also a realtime insert that links its mask across channels
repair.trimSilence	Threshold-based leading/trailing silence removal	Clean exports and batch assets	File-level utility, not a live insert

repair.decrackle, repair.dehum, repair.denoiseClassical, and repair.dereverbClassical are causal and run as realtime inserts; each equals its offline function for the same settings, delayed by the latency the instance reports, and an offline-only setting (wavelet mode, WPE, the quantile estimator) is refused by name. repair.declick, repair.declip, and repair.trimSilence are not causal and stay offline.

Saturation

Processor	Implementation	Main use	Real-time notes
saturation.ampSim	Preamp drive → tone stack → optional power amp (sag/transformer/NFB) → cabinet voicing	Guitar/bass amp color insert	Discrete cab/cabModel/ampModel topology choices belong at construction time, not automation; the power stage's half-sample delay and the second microphone's path delay are always counted, so reported latency does not move with automation
saturation.bitcrusher	Bit-depth and/or sample-rate style degradation	Lo-fi texture	Keep output gain controlled
saturation.exciter	High-frequency harmonic generation and blend	Add brightness and perceived detail	Can become harsh quickly
saturation.hardClipper	Hard nonlinear transfer curve	Aggressive peak shaving and distortion	Use oversampling or conservative drive; the ADAA half sample is reported and the dry path of a blend is delayed to match
saturation.multibandExciter	Band-split exciter with per-band drive/blend	Add sparkle without overloading lows	Crossover and drive balance matter
saturation.overdrive	A 720 Hz high-passed clip path, gained and soft-clipped, summed with the direct signal; clipping runs at twice the host rate behind antiderivative anti-aliasing, then a one-pole tone low-pass and an output level	Light breakup that keeps the low end	Realtime multichannel insert; reported latency includes the oversampler and anti-aliasing delay
saturation.distortion	Gain, a gain-bandwidth low-pass, then two hard clips with a coupling high-pass between them, with the same oversampling, tone and level frame	Heavier, tighter distortion	Realtime multichannel insert; same latency accounting as overdrive
saturation.softClipper	Smooth nonlinear curve	Gentle peak rounding	Common before maximizers
saturation.tape	Nonlinear saturation with tone/soft compression behavior, evaluated without small-signal cancellation error	Tape-like density	Drive changes loudness and tone together
saturation.transformer	Low-order harmonic coloration and subtle saturation, evaluated without small-signal cancellation error	Analog-style thickness	Usually subtle mastering color
saturation.tube	Asymmetric nonlinear transfer emphasizing musical harmonics	Warmth and vocal/instrument color	Watch DC and low-frequency buildup
saturation.waveshaper	Configurable nonlinear transfer curve	General distortion and coloration	Parameter smoothing prevents clicks

Spectral and Stereo

Processor	Implementation	Main use	Real-time notes
spectral.airBand	High-frequency shelf/exciter style enhancement	Add air above the main presence range	Pair with de-esser if sibilance increases
spectral.lowEndFocus	Low-band shaping and focus control	Tighten bass and reduce muddiness	Mono compatibility is important
spectral.presenceEnhancer	Presence-band shaping with controlled harmonic/detail emphasis	Improve vocal or lead audibility	Avoid masking-sensitive overuse
spectral.spectralShaper	Broad spectral tilt/shape correction	Match tonal contour or smooth harsh ranges	More transparent with moderate settings
stereo.autoPan	LFO-driven pan movement	Creative movement	More creative than mastering-neutral
stereo.binaural	Measured-HRTF virtual-speaker rendering with optional speaker crosstalk cancellation and azimuth motion	Place a stereo pair in headphone or speaker virtual space	Stereo-pair processor; use the full PlaybackRenderer when you also need layout conversion, room, or head tracking
stereo.haasEnhancer	Short inter-channel delay for width	Perceived width increase	Can reduce mono compatibility
stereo.imager	Mid/side width gain and optional band awareness	Widen or narrow stereo image	Check correlation and mono sum
stereo.monoMaker	Low-frequency mono summing below a crossover	Stabilize bass in the center	Common before final limiting
stereo.phaseAlign	Delay/polarity style alignment correction	Improve stereo phase relationship	Requires careful listening or measurement
stereo.stereoBalance	L/R or M/S balance adjustment	Correct image lean	Low latency

Reference Matching and Analysis

Name	Implementation	Main use
match.applyMatchEq	Applies an EQ curve derived from source/reference spectral difference	Move source tonal balance toward a reference
match.alignReferenceToSource	Estimates and compensates reference delay relative to source	Make A/B comparisons and match curves more reliable
match.abSwitch	Switches between source and reference paths	Audition comparison
match.abCrossfade	Crossfades between source and reference paths	Smooth comparison without clicks
match.referenceLoudness	Measures reference loudness metrics	Level-match comparisons
match.tonalBalance	Compares band energy distribution	Broad tonal comparison
match.tonalBalanceLogBands	Tonal balance on logarithmic bands	Perceptually useful reference comparison
match.matchEqCurve	Estimates a corrective EQ curve	Build match EQ settings
match.estimateReferenceDelaySamples	Estimates reference delay in samples	Align files before comparison
stereo.monoCompatCheck	Computes mono compatibility metrics	Catch phase and cancellation problems
stereo.monoCompatCheckLogBands	Mono compatibility by logarithmic bands	Find frequency ranges with stereo problems

Effects and Editing DSP

DSP	Implementation	Main use	Real-time notes
HPSS / harmonic / percussive	Median filtering on spectral representation separates horizontal harmonic energy and vertical percussive energy	Remixing, pre-processing, analysis cleanup	Offline-oriented for full files
Time stretch	Phase-vocoder style processing	Change duration without changing pitch	Streaming requires overlap/state discipline
Pitch shift	Resampling combined with time stretching	Transpose pitch while preserving approximate duration	Formants are not preserved unless using the voice-change path
Pitch correction	Pitch estimation and correction toward a target MIDI note	Vocal or monophonic note tuning	Best on monophonic material
Note stretch	Region-based stretch around a note span	Edit note duration	Offline editing operation
Voice change	Pitch and formant controls; the pitch stage shifts by exactly 2^(semitones/12)	Voice transformation	More expensive than simple pitch shift; also the voice.changer realtime insert for mono and stereo strips
Normalize	Peak or target-level gain adjustment	Utility level matching	File-level operation unless gain is known ahead
Trim/split silence	Threshold segmentation	Batch cleanup and asset prep	File-level utility
Reverb inserts	Plate/Dattorro, FDN, velvet, convolution, geometric room, and room-morph inserts	Space, ambience, and room-character morphing in mixer/mastering insert graphs	Build flags and IR requirements vary
Modulation/delay inserts	Chorus, ensemble, flanger, phaser, wah, auto-wah, rotary, ring modulator, pitch shifter, and stereo delay DSP live in source modules	Building blocks for creative FX	Exposed through insert factories and scene inserts; every ID is also callable through the generic masteringProcess / mastering_process registry, but there are no dedicated top-level JS/Python helper functions

Reverb insert availability

effects.reverb.plate / effects.reverb.dattorro, effects.reverb.fdn, effects.reverb.velvet, effects.reverb.convolution, and the modulation/delay inserts require SONARE_HAVE_FX. effects.reverb.room and effects.acoustic.roomMorph also require BUILD_ACOUSTIC_SIM.

Algorithmic and geometric room reverb are streamable. Convolution accepts a base64 float32 IR through insert params, or synthesizes a decaying-noise IR from decaySec and seed when omitted.

Modulation, Delay, Filter and Utility Inserts

These inserts are built from small modules under src/effects/ and src/mastering/utility/. Each is a realtime insert, listed in Insert Effects with its parameters.

Processor	Implementation	Main use
effects.modulation.chorus	Stereo chorus: fractional delay lines swept by low-frequency oscillators, optional one-pole section in front	Thicken and widen a source
effects.modulation.ensemble	Three delay taps per channel, 120 degrees apart, modulated by a slow and a fast oscillator at once; band-limited	String-machine style shimmer
effects.modulation.flanger	A loop closed around a modulated delay; the sign of the feedback sets where the comb's teeth sit	Sweeping comb-filter motion
effects.modulation.phaser	A cascade of first-order all-pass sections sharing one corner, mixed against the dry signal; one notch per two sections	Soft sweeping notches
effects.modulation.wah	Resonant band-pass swept by an oscillator	Rhythmic filter sweep
effects.modulation.autoWah	Resonant band-pass driven by the input's envelope	Touch-responsive filter sweep
effects.modulation.rotary	Dual-rotor Doppler and tremolo; each rotor glides to its target speed with separate spin-up and spin-down time constants	Rotating-speaker movement
effects.modulation.pitchShifter	Time-domain shifter built from two crossfaded delay taps	Small, low-latency detuning
effects.modulation.ringModulator	Input multiplied by a sinusoidal carrier	Metallic, inharmonic tones
effects.delay.stereo	Zero-latency stereo feedback delay; the left and right lines feed the loop and two panned feed-forward taps read the mono input	Echo and ping-pong patterns
effects.filter.vowel	Three parallel band-pass filters beside a direct path, with an optional drive in front; one control moves continuously between vowels	Speech-like filter movement
effects.gsEfx	GS insertion-effect unit with a selected type and 20 raw parameter bytes	GS-authored MIDI effect types
utility.gain	Broadband level trim	Level matching inside a chain

Nine catalog entries expose mixLaw, which chooses how the dry and wet paths are weighted at a given dryWet: six of the entries above (the chorus, ensemble, flanger, pitch shifter, ring modulator and stereo delay), the Dattorro reverb and its plate alias, and the bitcrusher. See Dry/wet mix law.

Mixing DSP

The mixer is DSP as well as routing.

Channel strips apply input trim, polarity, delay alignment, pan law, stereo width, insert processing, fader, mute/solo logic, sends, and metering.

Buses sum routed signals, VCA groups apply control gain, and meters compute peak/RMS/LUFS-like values, true peak, gain reduction, correlation, and goniometer buffers.

Automation lanes are sample-positioned and support linear, exponential, hold, and s-curve interpolation. Topology changes compile a routing graph; the audio processing path uses the compiled graph and preallocated state.

Real-Time Engine DSP Boundary

RealtimeEngine owns transport, tempo synchronization, graph runtime, clip playback, metronome, capture, monitor runtime, offline bounce, and telemetry.

It is not a replacement for the mastering processor registry. It is the scheduler and graph runtime that can host real-time-safe DSP blocks.

File-wide analysis, the non-causal repair stages (declick, declip, trim silence), and loudness optimization remain offline or latency-tolerant operations; the causal repair stages (decrackle, dehum, denoise, dereverb) can run live as inserts.

Realtime processing has to finish with the current block of audio before the next one arrives. That rules out anything that:

• needs to see the whole file before deciding;
• rebuilds a large buffer;
• requires unbounded or unpreallocated lookahead.

A bounded lookahead delay with preallocated storage can run in realtime; it still adds latency. The callback deadline and prepared state are the constraints.

Conversely, EQ, simple gain, short delays, and stateful compressors are easy to host in realtime once they have been prepared.

Grounding

This page is source-grounded rather than generated from marketing names. It uses these kinds of evidence:

Evidence this page uses

Evidence	Examples
Registry	src/mastering/api/named_processor_registry.cpp for public processor names
Header comments	compressor.h describes a feed-forward compressor with soft knee and makeup gain; linear_phase.h describes an FFT-domain linear-phase FIR equalizer
Config fields	TruePeakLimiterConfig exposes lookahead_ms, release_ms, oversample_factor, and apply_gain_at_input_rate; DenoiseClassicalConfig exposes three gain functions (LogMMSE, MMSE-STSA, spectral subtraction) and three noise estimators (Quantile, MCRA, IMCRA)
Runtime contracts	Several processors mark which parameters are real-time safe, and which changes resize buffers or rebuild FIR kernels
Implementation includes	Repair code includes LPC helpers for declick/declip; denoise uses NoiseTracker; convolution reverb and linear-phase EQ use partitioned convolution

Where this page says "main use", it describes the public intent implied by the processor name, config, and header comment. It does not claim hidden model behavior beyond the source.