Piano frequency

[fonsp]

Hey! Here is a little function to get the piano frequency of a Pitch, using the table https://upload.wikimedia.org/wikipedia/commons/a/ad/Piano_key_frequencies.png

const frequency_octave_4 = Dict(
    C => 261.626,
    C♯ => 277.183,
    D => 293.665,
    D♯ => 311.127,
    E => 329.628,
    F => 349.228,
    F♯ => 369.994,
    G => 391.995,
    G♯ => 415.305,
    A => 440,
    A♯ => 466.164,
    B => 493.883,
)

function frequency(pitch::Pitch)
    freq_at_4 = frequency_octave_4[pitch.class]
    transposition = pitch.octave - 4

    freq_at_4 * (2.0 ^ transposition)
end

[dpsanders]

Thanks! Here's my version:

julia> using MusicTheory, MusicTheory.PitchNames

julia> abstract type Temperament end

julia> struct EqualTemperament
           base_pitch::Pitch
           base_frequency::Float64
       end

julia> temperament = EqualTemperament(A[4], 440)
EqualTemperament(A₄, 440.0)

julia> function frequency(temperament::EqualTemperament, pitch::Pitch)
           semitone_distance = semitone(pitch) - semitone(temperament.base_pitch)
           return 2.0^(semitone_distance // 12)
       end
frequency (generic function with 1 method)

julia> frequency(temperament, C[4])
0.5946035575013605

julia> function frequency(temperament::EqualTemperament, pitch::Pitch)
           semitone_distance = semitone(pitch) - semitone(temperament.base_pitch)
           return 2.0^(semitone_distance // 12) * temperament.base_frequency
       end
frequency (generic function with 1 method)

julia> frequency(temperament, C[4])
261.6255653005986

[dpsanders]

I'll add a frequency.jl file.

[dpsanders]

Done in https://github.com/JuliaMusic/MusicTheory.jl/pull/24.

Thanks!