Music.Theory.Tuning.Scala

Parser for the Scala scale file format. See http://www.huygens-fokker.org/scala/scl_format.html for details. This module succesfully parses all 4115 scales in v.77 of the scale library.

Documentation

type Pitch i = Either Cents (Ratio i)

A .scl pitch is either in Cents or is a Ratio.

type Scale i = (String, i, [Pitch i])

A scale has a description, a degree, and a list of Pitches.

scale_description :: Scale i -> String

Text description of scale.

scale_degree :: Scale i -> i

The degree of the scale (number of Pitches).

scale_pitches :: Scale i -> [Pitch i]

The Pitches at Scale.

scale_octave :: Scale i -> Maybe (Pitch i)

The last Pitch element of the scale (ie. the ocatve).

perfect_octave :: Integral i => Scale i -> Bool

Is scale_octave perfect, ie. Ratio of 2 or Cents of 1200.

scale_pitch_representations :: Integral t => Scale i -> (t, t)

A pair giving the number of Cents and number of Ratio pitches at Scale.

pitch_cents :: Pitch Integer -> Cents

Pitch as Cents, conversion by to_cents_r if necessary.

type Epsilon = Double

pitch_ratio :: Epsilon -> Pitch Integer -> Rational

Pitch as Rational, conversion by reconstructed_ratio if necessary, hence epsilon.

scale_uniform :: Epsilon -> Scale Integer -> Scale Integer

Make scale pitches uniform, conforming to the most promininent pitch type.

scale_cents :: Scale Integer -> [Cents]

Scale as list of Cents (ie. pitch_cents) with 0 prefix.

scale_ratios :: Epsilon -> Scale Integer -> [Rational]

Scale as list of Rational (ie. pitch_ratio) with 1 prefix.

comment_p :: String -> Bool

Comment lines being with !.

filter_cr :: String -> String

Remove r.

p_or :: [a -> Bool] -> a -> Bool

Logical or of list of predicates.

remove_eol_comments :: String -> String

Remove to end of line ! comments.

filter_comments :: [String] -> [String]

Remove comments and null lines.

 filter_comments ["!a","b","","c"] == ["b","c"]

delete_trailing_point :: String -> String

Delete trailing ., read fails for 700..

pitch :: (Read i, Integral i) => String -> Pitch i

Pitches are either cents (with decimal point) or ratios (with /).

 map pitch ["700.0","3/2","2"] == [Left 700,Right (3/2),Right 2]

pitch_ln :: (Read i, Integral i) => String -> Pitch i

Pitch lines may contain commentary.

parse :: (Read i, Integral i) => String -> Scale i

Parse .scl file.

load :: (Read i, Integral i) => FilePath -> IO (Scale i)

Load .scl file.

 s <- load "/home/rohan/opt/scala/scl/xenakis_chrom.scl"
 scale_pitch_representations s == (6,1)
 scale_ratios 1e-3 s == [1,21/20,29/23,179/134,280/187,11/7,100/53,2]

dir_subset :: [String] -> FilePath -> IO [FilePath]

Subset of files in dir with an extension in ext.

load_dir :: (Read i, Integral i) => FilePath -> IO [Scale i]

Load all .scl files at dir.

 db <- load_dir "/home/rohan/opt/scala/scl"
 length db == 4115
 length (filter ((== 0) . scale_degree) db) == 1
 length (filter (== Just (Right 2)) (map scale_octave db)) == 3562

 let r = [0,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24
         ,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44
         ,45,46,47,48,49,50,51,53,54,55,56,57,58,59,60,61,62,63,64
         ,65,66,67,68,69,70,71,72,74,75,77,78,79,80,81,84,87,88
         ,90,91,92,95,96,99,100,101,105,110,112,117,118,130,140,171
         ,180,271,311,342,366,441,612]
 in nub (sort (map scale_degree db)) == r

 let r = ["Xenakis's Byzantine Liturgical mode, 5 + 19 + 6 parts"
         ,"Xenakis's Byzantine Liturgical mode, 12 + 11 + 7 parts"
         ,"Xenakis's Byzantine Liturgical mode, 7 + 16 + 7 parts"]
 in filter (isInfixOf "Xenakis") (map scale_description db) == r

 length (filter (not . perfect_octave) db) == 544

 mapM_ (putStrLn.scale_description) (filter (not . perfect_octave) db)