Added Frequency conversions (#154)

* added function and teests * added functions for frequency conversions * forgot to export new functions * removed erroneous export that i added accidentally * fixed some formatting and removed two functions * added changes to changelog * Update CHANGELOG.md Co-authored-by: George Datseris <[email protected]> * Update Project.toml Co-authored-by: George Datseris <[email protected]> * Update src/note.jl Co-authored-by: George Datseris <[email protected]> * Update src/note.jl Co-authored-by: George Datseris <[email protected]> * Update src/note.jl Co-authored-by: George Datseris <[email protected]> * Update src/note.jl Co-authored-by: George Datseris <[email protected]>
JuliaMusic · Feb 8, 2022 · ba0237d · ba0237d
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -4,6 +4,8 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
+# v2.2.0
+* New functions `pitch_to_hz ` and `hz_to_pitch `
 # v2.1.0
 * Default value of `MIDIFile.format` changed from 0 to 1
 * Warning introduced to `fileio_save` for format 0 files with multiple tracks

diff --git a/Project.toml b/Project.toml
@@ -1,7 +1,7 @@
 name = "MIDI"
 uuid = "f57c4921-e30c-5f49-b073-3f2f2ada663e"
 repo = "https://github.com/JuliaMusic/MIDI.jl.git"
-version = "2.1.0"
+version = "2.2.0"
 
 [deps]
 FileIO = "5789e2e9-d7fb-5bc7-8068-2c6fae9b9549"

diff --git a/src/MIDI.jl b/src/MIDI.jl
@@ -31,6 +31,7 @@ export getnotes, addnote!, addnotes!, addevent!, addevents!
 export MIDITrack
 export Note, Notes, AbstractNote, DrumNote
 export pitch_to_name, name_to_pitch
+export pitch_to_hz, hz_to_pitch
 export TrackEvent, MetaEvent, MIDIEvent, SysexEvent
 export readvariablelength, writevariablelength
 

diff --git a/src/note.jl b/src/note.jl
@@ -181,6 +181,24 @@ function name_to_pitch(name)
     return pitch + x + 12(octave+1) # lowest possible octave is -1 but pitch starts from 0
 end
 
+"""
+    pitch_to_hz(pitch::Integer, A4::Real = 440) -> hz::Real
+Return the frequency value of the given midi note, optionally given the reference for middle A.
+See https://en.wikipedia.org/wiki/Piano_key_frequencies
+and https://librosa.org/doc/main/_modules/librosa/core/convert.html#midi_to_hz.
+"""
+function pitch_to_hz(pitch, A4 = 440)
+    return A4 * (2^ ((pitch-69) / 12))
+end
+
+"""
+    hz_to_pitch(hz::Real, A4::Real = 440) -> pitch::Int
+Inverse of [`pitch_to_hz`](@ref).
+"""
+function hz_to_pitch(freq, A4 = 440)
+    return 12 * (log2(freq) - log2(A4)) + 69
+end
+
 #######################################################
 # pretty printing
 #######################################################

diff --git a/test/note.jl b/test/note.jl
@@ -32,6 +32,21 @@ end
 
     @test all([name_to_pitch(pitch_to_name(i)) == i for i in 0:255])
 end
+@testset "frequency" begin
+    tol = 10e-3
+    @test pitch_to_hz(69,440)==440
+    @test pitch_to_hz(69,432)==432
+    @test abs( pitch_to_hz(44)-103.8262 ) < tol
+    @test abs(pitch_to_hz(105)-3520.000) < tol
+    @test abs(pitch_to_hz(89,432)-1371.51) < tol
+    #hz to pitch
+    @test hz_to_pitch(440) == 69
+    @test hz_to_pitch(432,432) == 69
+    @test round(hz_to_pitch(7040.000)) == 117
+    @test round(hz_to_pitch(123.4708)) == 47
+
+
+end
 
 @testset "copying notes" begin
     midi = load("doxy.mid")