Introduction

HarmTrace (Harmony Analysis and Retrieval of Music with Type-level Representations of Abstract Chords Entities) is a system for automatic harmony analysis of music. It takes a sequence of chords as input and produces a harmony analysis, which can be visualised as a tree.

Music theory has been essential in composing and performing music for centuries. Within Western tonal music, from the early Baroque on to modern-day jazz and pop music, the function of chords within a chord sequence can be explained by harmony theory. Although Western tonal harmony theory is a thoroughly studied area, formalising this theory is a hard problem.

With HarmTrace we have developed a formalisation of the rules of tonal harmony as a Haskell (generalized) algebraic datatype. Given a sequence of chord labels, the harmonic function of a chord in its tonal context is automatically derived. For this, we use several advanced functional programming techniques, such as type-level computations, datatype-generic programming, and error-correcting parsers. Our functional model of harmony offers various benefits: it can be used to define harmonic similarity measures and facilitate music retrieval, or it can help musicologists in batch-analysing large corpora of digitised scores, for instance.

HarmTrace is covered in depth in the following papers:

de Haas, W. B., et al. "Automatic Functional Harmonic Analysis." Computer Music Journal 37.4 (2013): 37-53. (PDF)

Magalhaes, J. P., & de Haas, W. B. (2011, September). Functional modelling of musical harmony: an experience report. In ACM SIGPLAN Notices (Vol. 46, No. 9, pp. 156-162). ACM. (PDF)

Installation

Because the main authors of HarmTrace are are no longer affiliated with academic institutions and HarmTrace is only modestly maintained, installing Harmtrace can be a challenge. However, Stack helps considerably. One of the difficulties is that HarmTrace currently only build on a relatively old version of GHC, namely 7.10. Provided that you have intalled a Haskell system and pulled this repository, Stack should take care of it:

stack init --solver --install-ghc

stack build

Running HarmTrace

You can use Stack to run HarmTrace:

>>> stack exec harmtrace
harmtrace [COMMAND] ... [OPTIONS]
  Harmonic Analysis and Retrieval of Music

Commands:
  parse      Parse files into harmonic analysis trees
  match      Harmonic similarity matching
  recognise  Recognise chords from audio files

  -r=file            File to read flags from
  -?      --help     Display help message
  -V      --version  Print version information

All modes have separate help pages:

>>> stack exec harmtrace parse -- --help
parse [OPTIONS]
  Parse files into harmonic analysis trees

  -g      --grammar=string    Grammar to use (jazz|pop)
  -c      --chords=string     Input chord sequence to parse
  -i      --file=filepath     Input file to parse
  -d      --dir=filepath      Input directory to parse all files within
  -o      --out=filepath      Output binary file to write parse results to
  -k      --key=filepath      Ground-truth key annotation file
  -x      --key-dir=filepath  Ground-truth key annotation directory
  -p      --print             Output a .png of the parse tree
  -s      --print-insertions  Show inserted nodes
  -r=file                     File to read flags from
  -?      --help              Display help message
  -V      --version           Print version information

You can parse a chord sequence with --chords the chord should be in Harte syntax suffixed with a ;INT indicating the duration of the chord and separated by spaces. The first 'chord' represents a key signature. For instance:

>>> stack exec harmtrace parse -- --grammar=jazz --chords="C:maj D:min;1 G:7;2 C:maj;1"
parsed 3 chords into 1 analysis tree(s)
[Piece[PD[D_1_1[S_1par_1[IIm_1[D:min]]][D_2_1[V7_2[G:7]]]]][PT[T_1_1[I_1[C:maj]]]]]

If you add --print, HarmTrace will render a .PNG image for you using https://ironcreek.net/phpsyntaxtree/