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_NOEXCEPT
	Construct with standalone Beat.

	Backbeat (shared_ptr< Beat > beatDetector)
	Construct with shared Beat.

	Backbeat (shared_ptr< Beat > beatDetector, shared_ptr< Downbeat > downbeatDetector)
	Construct with shared Beat and Downbeat.

	~Backbeat () FL_NOEXCEPT override

void	fireCallbacks () override

float	getBackbeatRatio () const
	Returns ratio of backbeat to downbeat energy (0-2+)

float	getConfidence () const
	Returns backbeat detection confidence (0-1)

u8	getLastBackbeatNumber () const
	Returns the beat number of the last detected backbeat (1-based)

const char *	getName () const override

float	getStrength () const
	Returns current backbeat accent strength (0-1+)

bool	isBackbeat () const
	Returns true if backbeat was detected this frame.

bool	needsFFT () const override

bool	needsFFTHistory () const override

void	reset () override

void	setAdaptive (bool enable)
	Enable/disable adaptive threshold learning (default: true)

void	setBackbeatExpectedBeats (u8 beatMask)
	Set which beats are backbeats using bitmask (bit 0=beat 1, bit 1=beat 2, etc.)

void	setBassThreshold (float threshold)
	Set bass accent threshold (default: 1.2)

void	setBeatDetector (shared_ptr< Beat > beatDetector)
	Share an external Beat instance.

void	setConfidenceThreshold (float threshold)
	Set minimum confidence for backbeat detection (default: 0.6)

void	setDownbeatDetector (shared_ptr< Downbeat > downbeatDetector)
	Share an external Downbeat instance.

void	setHighThreshold (float threshold)
	Set high accent threshold (default: 1.1)

void	setMidThreshold (float threshold)
	Set mid accent threshold (default: 1.3) - critical for snare.

void	update (shared_ptr< Context > context) override

Public Member Functions inherited from fl::audio::Detector
virtual	~Detector () FL_NOEXCEPT=default

virtual void	setSampleRate (int) FL_NOEXCEPT

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)

float	calculatePatternConfidence (const fft::Bins &fft)

bool	detectBackbeat (float accentStrength, const fft::Bins &fft)

float	detectBackbeatAccent (const MultibandAccent &accent)

bool	isBackbeatPosition () const

void	updateAdaptiveThresholds ()

void	updateBackbeatProfile (const fft::Bins &fft)

void	updateBeatDetector (shared_ptr< Context > context)

void	updateBeatPosition ()

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

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

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

Detailed Description

Public Member Functions

Public Attributes

Private Member Functions

Private Attributes

Static Private Attributes