fl::audio::detector::Backbeat Class Reference

Detailed Description

Detects backbeats (beats 2 and 4 in 4/4 time) in music.

The Backbeat identifies backbeat patterns using multi-band frequency analysis with emphasis on mid-range frequencies where snare drums are prominent. It complements the Downbeat and is crucial for rock, pop, funk, and many other genres where the snare drum emphasizes the backbeat.

Features:

• Multi-band accent detection (bass, mid, high)
• Adaptive threshold learning
• Spectral profile matching
• Works standalone or with Downbeat
• Confidence scoring
• Pattern consistency checking

Dependencies:

• Requires Beat for rhythm analysis
• Optional Downbeat for accurate measure position
• Uses FFT for frequency analysis

Definition at line 45 of file backbeat.h.

#include <backbeat.h>

Inheritance diagram for fl::audio::detector::Backbeat:

Collaboration diagram for fl::audio::detector::Backbeat:

Public Member Functions
	Backbeat () FL_NO_EXCEPT
	Construct with standalone Beat.
	Backbeat (shared_ptr< Beat > beatDetector) FL_NO_EXCEPT
	Construct with shared Beat.
	Backbeat (shared_ptr< Beat > beatDetector, shared_ptr< Downbeat > downbeatDetector) FL_NO_EXCEPT
	Construct with shared Beat and Downbeat.
	~Backbeat () FL_NO_EXCEPT override
void	fireCallbacks () FL_NO_EXCEPT override
float	getBackbeatRatio () const FL_NO_EXCEPT
	Returns ratio of backbeat to downbeat energy (0-2+)
float	getConfidence () const FL_NO_EXCEPT
	Returns backbeat detection confidence (0-1)
u8	getLastBackbeatNumber () const FL_NO_EXCEPT
	Returns the beat number of the last detected backbeat (1-based)
const char *	getName () const FL_NO_EXCEPT override
float	getStrength () const FL_NO_EXCEPT
	Returns current backbeat accent strength (0-1+)
bool	isBackbeat () const FL_NO_EXCEPT
	Returns true if backbeat was detected this frame.
bool	needsFFT () const FL_NO_EXCEPT override
bool	needsFFTHistory () const FL_NO_EXCEPT override
void	reset () FL_NO_EXCEPT override
void	setAdaptive (bool enable) FL_NO_EXCEPT
	Enable/disable adaptive threshold learning (default: true)
void	setBackbeatExpectedBeats (u8 beatMask) FL_NO_EXCEPT
	Set which beats are backbeats using bitmask (bit 0=beat 1, bit 1=beat 2, etc.)
void	setBassThreshold (float threshold) FL_NO_EXCEPT
	Set bass accent threshold (default: 1.2)
void	setBeatDetector (shared_ptr< Beat > beatDetector) FL_NO_EXCEPT
	Share an external Beat instance.
void	setConfidenceThreshold (float threshold) FL_NO_EXCEPT
	Set minimum confidence for backbeat detection (default: 0.6)
void	setDownbeatDetector (shared_ptr< Downbeat > downbeatDetector) FL_NO_EXCEPT
	Share an external Downbeat instance.
void	setHighThreshold (float threshold) FL_NO_EXCEPT
	Set high accent threshold (default: 1.1)
void	setMidThreshold (float threshold) FL_NO_EXCEPT
	Set mid accent threshold (default: 1.3) - critical for snare.
void	update (shared_ptr< Context > context) FL_NO_EXCEPT override
Public Member Functions inherited from fl::audio::Detector
virtual	~Detector () FL_NO_EXCEPT=default
virtual void	setSampleRate (int) FL_NO_EXCEPT

Public Attributes
function_list< void(u8 beatNumber, float confidence, float strength)>	onBackbeat
	Fires on detected backbeat (beats 2, 4) with beat number, confidence, and strength.

Private Member Functions
MultibandAccent	calculateMultibandAccent (const fft::Bins &fft) FL_NO_EXCEPT
float	calculatePatternConfidence (const fft::Bins &fft) FL_NO_EXCEPT
bool	detectBackbeat (float accentStrength, const fft::Bins &fft) FL_NO_EXCEPT
float	detectBackbeatAccent (const MultibandAccent &accent) FL_NO_EXCEPT
bool	isBackbeatPosition () const FL_NO_EXCEPT
void	updateAdaptiveThresholds () FL_NO_EXCEPT
void	updateBackbeatProfile (const fft::Bins &fft) FL_NO_EXCEPT
void	updateBeatDetector (shared_ptr< Context > context) FL_NO_EXCEPT
void	updateBeatPosition () FL_NO_EXCEPT

Private Attributes
bool	mAdaptive
float	mAdaptiveThreshold
deque< float >	mBackbeatAccents
bool	mBackbeatDetected
u8	mBackbeatMask
float	mBackbeatMean
float	mBackbeatRatio
vector< float >	mBackbeatSpectralProfile
float	mBassThreshold
shared_ptr< Beat >	mBeatDetector
u8	mBeatsPerMeasure
float	mConfidence
float	mConfidenceThreshold
u8	mCurrentBeat
float	mCurrentStrength
shared_ptr< Downbeat >	mDownbeatDetector
float	mHighThreshold
u8	mLastBackbeatNumber
float	mMidThreshold
deque< float >	mNonBackbeatAccents
float	mNonBackbeatMean
bool	mOwnsBeatDetector
bool	mOwnsDownbeatDetector
MultibandAccent	mPreviousAccent
bool	mPreviousWasBeat
float	mProfileAlpha
shared_ptr< const fft::Bins >	mRetainedFFT

Static Private Attributes
static constexpr size	MAX_ACCENT_HISTORY = 16
static constexpr size	SPECTRAL_PROFILE_SIZE = 16

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The documentation for this class was generated from the following files:

• fl/audio/detector/backbeat.h
• fl/audio/detector/backbeat.cpp.hpp