Key¶

streaming mode | Tonal category

Inputs¶

pcp (vector_real) - the input pitch class profile

Outputs¶

key (string) - the estimated key, from A to G

scale (string) - the scale of the key (major or minor)

strength (real) - the strength of the estimated key

Parameters¶

averageDetuningCorrection (bool ∈ {true, false}, default = true) :
shifts a pcp to the nearest tempered bin

numHarmonics (integer ∈ [1, ∞), default = 4) :
number of harmonics that should contribute to the polyphonic profile (1 only considers the fundamental harmonic)

pcpSize (integer ∈ [12, ∞), default = 36) :
number of array elements used to represent a semitone times 12 (this parameter is only a hint, during computation, the size of the input PCP is used instead)

pcpThreshold (real ∈ [0, 1], default = 0.2) :
pcp bins below this value are set to 0

profileType (string ∈ {diatonic, krumhansl, temperley, weichai, tonictriad, temperley2005, thpcp, shaath, gomez, noland, edmm, edma, bgate, braw}, default = bgate) :
the type of polyphic profile to use for correlation calculation

slope (real ∈ [0, ∞), default = 0.6) :
value of the slope of the exponential harmonic contribution to the polyphonic profile

useMajMin (bool ∈ {true, false}, default = false) :
songs can also be clasified as MajMin [4]. Only avalable for the edma, bgate and braw profiles

usePolyphony (bool ∈ {true, false}, default = true) :
enables the use of polyphonic profiles to define key profiles (this includes the contributions from triads as well as pitch harmonics)

useThreeChords (bool ∈ {true, false}, default = true) :
consider only the 3 main triad chords of the key (T, D, SD) to build the polyphonic profiles

Description¶

This algorithm computes key estimate given a pitch class profile (HPCP). The algorithm was severely adapted and changed from the original implementation for readability and speed.

Key will throw exceptions either when the input pcp size is not a positive multiple of 12 or if the key could not be found. Also if parameter “scale” is set to “minor” and the profile type is set to “weichai”

Abouth the Key Profiles:

‘Diatonic’ - binary profile with diatonic notes of both modes. Could be useful for ambient music or diatonic music which is not strictly ‘tonal functional’.

‘Tonic Triad’ - just the notes of the major and minor chords. Exclusively for testing.

‘Krumhansl’ - reference key profiles after cognitive experiments with users. They should work generally fine for pop music.

‘Temperley’ - key profiles extracted from corpus analysis of euroclassical music. Therefore, they perform best on this repertoire (especially in minor).

‘Shaath’ - profiles based on Krumhansl’s specifically tuned to popular and electronic music.

‘Noland’ - profiles from Bach’s ‘Well Tempered Klavier’.

‘edma’ - automatic profiles extracted from corpus analysis of electronic dance music [3]. They normally perform better that Shaath’s

‘edmm’ - automatic profiles extracted from corpus analysis of electronic dance music and manually tweaked according to heuristic observation. It will report major modes (which are poorly represented in EDM) as minor, but improve performance otherwise [3].

‘braw’ - profiles obtained by calculating the median profile for each mode from a subset of BeatPort dataset. There is an extra profile obtained from ambiguous tracks that are reported as minor [4]

‘bgate’ - same as braw but zeroing the 4 less relevant elements of each profile [4]

The standard mode of the algorithm estimates key/scale for a given HPCP vector.

The streaming mode first accumulates a stream of HPCP vectors and computes its mean to provide the estimation. In this mode, the algorithm can apply a tuning correction, based on peaks in the bins of the accumulated HPCP distribution [3] (the averageDetuningCorrection parameter). This detuning approach requires a high resolution of the input HPCP vectors (pcpSize larger than 12).

References:

[1] E. Gómez, “Tonal Description of Polyphonic Audio for Music Content Processing,” INFORMS Journal on Computing, vol. 18, no. 3, pp. 294–304, 2006.

[2] D. Temperley, “What’s key for key? The Krumhansl-Schmuckler key-finding algorithm reconsidered”, Music Perception vol. 17, no. 1, pp. 65-100, 1999.

[3] Á. Faraldo, E. Gómez, S. Jordà, P.Herrera, “Key Estimation in Electronic Dance Music. Proceedings of the 38th International Conference on information Retrieval, pp. 335-347, 2016.

[4] Faraldo, Á., Jordà, S., & Herrera, P. (2017, June). A multi-profile method for key estimation in edm. In Audio Engineering Society Conference: 2017 AES International Conference on Semantic Audio. Audio Engineering Society.

Source code¶

C++ source code

C++ header file