Code Quality Rank: L3
Programming language: Swift
License: GNU General Public License v3.0 or later
Tags: Utility    
Latest version: v3.0.0

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CI Status Version Carthage Compatible License Platform

Pitchy provides a simple way to get a music pitch from a frequency. Other than that it has a bunch of useful data structures, calculators and helper functions to work with notes, octaves and acoustic waves.

From Wikipedia:

Pitch is a perceptual property of sounds that allows their ordering on a frequency-related scale, or more commonly, pitch is the quality that makes it possible to judge sounds as "higher" and "lower" in the sense associated with musical melodies.

Table of Contents

Key features

  • Get lower, higher and closest pitch offsets from a specified frequency.
  • Get an acoustic wave with wavelength, period and harmonics.
  • Create a note from a pitch index, frequency or a letter with octave number.
  • Calculate a frequency, note letter and octave from a pitch index
  • Find a pitch index from a specified frequency or a note letter with octave.
  • Convert a frequency to wavelength and vice versa.
  • Convert a wavelength to time period and vice versa.



Create Pitch struct with a specified frequency to get lower, higher and closest pitch offsets:

do {
  // Frequency = 445 Hz
  let pitch = try Pitch(frequency: 445.0)
  let pitchOffsets = pitch.offsets

  print(pitchOffsets.lower.frequency)     // 5 Hz
  print(pitchOffsets.lower.percentage)    // 19.1%
  print(pitchOffsets.lower.note.index)    // 0
  print(pitchOffsets.lower.cents)         // 19.56

  print(pitchOffsets.higher.frequency)    // -21.164 Hz
  print(pitchOffsets.higher.percentage)   // -80.9%
  print(pitchOffsets.higher.note.index)   // 1
  print(pitchOffsets.higher.cents)        // -80.4338

  print(pitchOffsets.closest.note.string) // "A4"

  // You could also use acoustic wave
  print(pitch.wave.wavelength)            // 0.7795 meters
} catch {
  // Handle errors

Acoustic wave

Get an acoustic wave with wavelength, period and harmonics.

do {
  // AcousticWave(wavelength: 0.7795)
  // AcousticWave(period: 0.00227259)
  let wave = try AcousticWave(frequency: 440.0)

  print(wave.frequency)       // 440 Hz
  print(wave.wavelength)      // 0.7795 meters
  print(wave.period)          // 0.00227259 s
  print(wave.harmonics[0])    // 440 Hz
  print(wave.harmonics[1])    // 880 Hz
} catch {
  // Handle errors


Note could be created with a corresponding frequency, letter + octave number or a pitch index.

do {
  // Note(frequency: 261.626)
  // Note(letter: .C, octave: 4)
  let note = try Note(index: -9)

  print(note.index)                 // -9
  print(note.letter)                // .C
  print(note.octave)                // 4
  print(note.frequency)             // 261.626 Hz
  print(note.string)                // "C4"
  print(try note.lower().string)    // "B3"
  print(try note.higher().string)   // "C#4"
} catch {
  // Handle errors


Calculators are used in the initialization of Pitch, AcousticWave and Note, but also are included in the public API.

do {
  // PitchCalculator
  let pitchOffsets = try PitchCalculator.offsets(445.0)
  let cents = try PitchCalculator.cents(
    frequency1: 440.0,
    frequency2: 440.0
  ) // 19.56

  // NoteCalculator
  let frequency1 = try NoteCalculator.frequency(forIndex: 0)       // 440.0 Hz
  let letter = try NoteCalculator.letter(forIndex: 0)              // .A
  let octave = try NoteCalculator.octave(forIndex: 0)              // 4
  let index1 = try NoteCalculator.index(forFrequency: 440.0)       // 0
  let index2 = try NoteCalculator.index(forLetter: .A, octave: 4)  // 0

  // WaveCalculator
  let f = try WaveCalculator.frequency(forWavelength: 0.7795)      // 440.0 Hz
  let wl1 = try WaveCalculator.wavelength(forFrequency: 440.0)     // 0.7795 meters
  let wl2 = try WaveCalculator.wavelength(forPeriod: 0.00227259)   // 0.7795 meters
  let period = try WaveCalculator.period(forWavelength: 0.7795)    // 0.00227259 s
} catch {
  // Handle errors


With a help of FrequencyValidator it's possible to adjust minimum and maximum frequencies that are used for validations in all calculations:

FrequencyValidator.minimumFrequency = 20.0
FrequencyValidator.maximumFrequency = 4190.0

Error handling

Almost everything is covered with tests, but it's important to pass valid values, such as frequencies and pitch indexes. That's why there a re a list of errors that should be handled properly.

enum Error: ErrorType {
  case InvalidFrequency
  case InvalidWavelength
  case InvalidPeriod
  case InvalidPitchIndex
  case InvalidOctave


Pitchy is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod 'Pitchy'

Pitchy is also available through Carthage. To install just write into your Cartfile:

github "vadymmarkov/Pitchy"


Vadym Markov, [email protected]


Check the CONTRIBUTING file for more info.


Pitchy is available under the MIT license. See the LICENSE file for more info.

*Note that all licence references and agreements mentioned in the Pitchy README section above are relevant to that project's source code only.