What is the best way to create a function that shifts a musical note up or down by one semitone?

Question

What is the best way to create a function that shifts a musical note up or down by one semitone?

Currently developing a guitar tuning tool and facing some hurdles.

Striving to create a function that can take a musical note, an octave, and a direction (up or down), then produce a transposed note by a half step based on the traditional piano layout (i.e., transitioning from B to C will involve adjusting octaves).

The functionality should also handle sharps.

Some examples:

const tunedNoteUp = pitchShiftNoteByHalfStep({note: "B", octave: 3}, "up")
console.log(tunedNoteUp) // {note: "C", octave: 4}

const secondCase = pitchShiftNoteByHalfStep({note:"G#", octave: 4}, "up")
console.log(secondCase) // {note: "A", octave: 4}

const thirdCase = pitchShiftNoteByHalfStep({note: "A#", octave: 4}, "down")
console.log(thirdCase) // {note: "A", octave: 4}

Open to utilizing libraries but haven't found any suitable ones yet.

Current progress:

function pitchShiftNoteByHalfStep(note, octave, direction) {
  const notes = [ 'A', 'A#', 'B', 'C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#'];

  const index = notes.indexOf(note);
  const newIndex = direction === 'up' ? index + 1 : index - 1;
  const newNote = notes[newIndex >= 0 ? newIndex : 11];

  const newOctave = (octave + Math.floor((newIndex + (direction === 'up' ? 0 : 11)) / 12));

  return `${newNote}${newOctave}`
}

Encountering issues in certain scenarios like shifting G# upwards.

Thank you!

javascript typescript

Answer 1

Answer №1

Consider the following:

To make note management easier, start the array of note names with "C" as octaves start at C, not A.
Instead of using "up" and "down", pass a signed integer (1 for up, -1 for down) to allow for adding more than one half note at a time.
Utilize the remainder operator (%) for calculation convenience.

const NOTES = "C,C#,D,D#,E,F,F#,G,G#,A,A#,B".split(",");

function pitchShift({note, octave}, add) {
    const offset = NOTES.indexOf(note) + octave * 12 + add,
          noteNum = offset % 12;
    if (offset < 0 || offset >= 8*12) return null; // Indication of out-of-range.
    return {note: NOTES[noteNum], octave: (offset - noteNum) / 12};
}

// demo
let pitch = {note: "C", octave: 4};
console.log(JSON.stringify(pitch));
// Add 4 half notes to arrive at E:
pitch = pitchShift(pitch, 4);
console.log(JSON.stringify(pitch));
// Subtract 6 half notes to arrive at A# of previous octave
pitch = pitchShift(pitch, -6);
console.log(JSON.stringify(pitch));
// Add 3 half notes to arrive at C#:
pitch = pitchShift(pitch, 3);
console.log(JSON.stringify(pitch));
// Subtract 2 half notes to arrive at B:
pitch = pitchShift(pitch, -2);
console.log(JSON.stringify(pitch));
// Subtract to go to lowest pitch that is supported (C octave 0)
pitch = pitchShift(pitch, -47);
console.log(JSON.stringify(pitch));
// Subtract one more to get an out of range indication (null)
pitch = pitchShift(pitch, -1);
console.log(JSON.stringify(pitch));
// Define second-highest supported pitch (A# octave 7) and add 1 (B octave 7)
pitch = pitchShift({note: "A#", octave: 7}, 1);
console.log(JSON.stringify(pitch));
// Add one more to get an out of range indication (null)
pitch = pitchShift(pitch, 1);
console.log(JSON.stringify(pitch));

Answer 2

Consider the following:

To make note management easier, start the array of note names with "C" as octaves start at C, not A.
Instead of using "up" and "down", pass a signed integer (1 for up, -1 for down) to allow for adding more than one half note at a time.
Utilize the remainder operator (%) for calculation convenience.

const NOTES = "C,C#,D,D#,E,F,F#,G,G#,A,A#,B".split(",");

function pitchShift({note, octave}, add) {
    const offset = NOTES.indexOf(note) + octave * 12 + add,
          noteNum = offset % 12;
    if (offset < 0 || offset >= 8*12) return null; // Indication of out-of-range.
    return {note: NOTES[noteNum], octave: (offset - noteNum) / 12};
}

// demo
let pitch = {note: "C", octave: 4};
console.log(JSON.stringify(pitch));
// Add 4 half notes to arrive at E:
pitch = pitchShift(pitch, 4);
console.log(JSON.stringify(pitch));
// Subtract 6 half notes to arrive at A# of previous octave
pitch = pitchShift(pitch, -6);
console.log(JSON.stringify(pitch));
// Add 3 half notes to arrive at C#:
pitch = pitchShift(pitch, 3);
console.log(JSON.stringify(pitch));
// Subtract 2 half notes to arrive at B:
pitch = pitchShift(pitch, -2);
console.log(JSON.stringify(pitch));
// Subtract to go to lowest pitch that is supported (C octave 0)
pitch = pitchShift(pitch, -47);
console.log(JSON.stringify(pitch));
// Subtract one more to get an out of range indication (null)
pitch = pitchShift(pitch, -1);
console.log(JSON.stringify(pitch));
// Define second-highest supported pitch (A# octave 7) and add 1 (B octave 7)
pitch = pitchShift({note: "A#", octave: 7}, 1);
console.log(JSON.stringify(pitch));
// Add one more to get an out of range indication (null)
pitch = pitchShift(pitch, 1);
console.log(JSON.stringify(pitch));

Answer 3

Answer №2

Here's a different approach to this problem:

function adjustPitch(note, octave, direction) {
    const notes = ['A', 'A#', 'B', 'C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#'];
    const index = notes.indexOf(note);
    const newIndex = (notes.length + index + (direction === 'up' ? 1 : - 1)) % notes.length;
    const newNote = notes[newIndex];

    let octaveAdjustment = 0
    if (newIndex === 0 && direction === 'up') {
        octaveAdjustment = 1
    }
    if (newIndex === notes.length - 1 && direction === 'down') {
        octaveAdjustment = -1
    }

    const updatedOctave = octave + octaveAdjustment

    return `${newNote}${updatedOctave}`
}

Answer 4

Here's a different approach to this problem:

function adjustPitch(note, octave, direction) {
    const notes = ['A', 'A#', 'B', 'C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#'];
    const index = notes.indexOf(note);
    const newIndex = (notes.length + index + (direction === 'up' ? 1 : - 1)) % notes.length;
    const newNote = notes[newIndex];

    let octaveAdjustment = 0
    if (newIndex === 0 && direction === 'up') {
        octaveAdjustment = 1
    }
    if (newIndex === notes.length - 1 && direction === 'down') {
        octaveAdjustment = -1
    }

    const updatedOctave = octave + octaveAdjustment

    return `${newNote}${updatedOctave}`
}

Answer 5

Answer №3

As someone with limited musical knowledge, I find that arranging the notes in the array to match the piano layout makes your code more effective for octave shifting. The other solutions seem overly complex, leaving me wondering if I overlooked something important. Nonetheless, perhaps this insight can be beneficial.

const musicalNotes = ['C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A', 'A#', 'B'],
      maxOctave = 4,
      minOctave = 1;

function pitchShiftNoteByHalfStep(note, octave, direction) {
  let index = musicalNotes.indexOf(note),
      newIndex;

  if ('up' === direction) {
    if (index + 1 === musicalNotes.length) {
      newIndex = 0;
      octave++;

      if (octave > maxOctave) {
        octave = maxOctave;
        console.log('Warning: Limitting to max octave.');
      }
    }
    else {
      newIndex = index + 1;
    }
  }
  else if ('down' === direction) {
    if (0 === index) {
      newIndex = musicalNotes.length - 1;
      octave--;
      
      if (octave < minOctave) {
        octave = minOctave;
        console.log('Warning: Resetting to min octave.');
      }
    }
    else {
      newIndex = index - 1;
    }
  }

  return musicalNotes[newIndex] + '' + octave;
}

Answer 6

As someone with limited musical knowledge, I find that arranging the notes in the array to match the piano layout makes your code more effective for octave shifting. The other solutions seem overly complex, leaving me wondering if I overlooked something important. Nonetheless, perhaps this insight can be beneficial.

const musicalNotes = ['C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A', 'A#', 'B'],
      maxOctave = 4,
      minOctave = 1;

function pitchShiftNoteByHalfStep(note, octave, direction) {
  let index = musicalNotes.indexOf(note),
      newIndex;

  if ('up' === direction) {
    if (index + 1 === musicalNotes.length) {
      newIndex = 0;
      octave++;

      if (octave > maxOctave) {
        octave = maxOctave;
        console.log('Warning: Limitting to max octave.');
      }
    }
    else {
      newIndex = index + 1;
    }
  }
  else if ('down' === direction) {
    if (0 === index) {
      newIndex = musicalNotes.length - 1;
      octave--;
      
      if (octave < minOctave) {
        octave = minOctave;
        console.log('Warning: Resetting to min octave.');
      }
    }
    else {
      newIndex = index - 1;
    }
  }

  return musicalNotes[newIndex] + '' + octave;
}

Answer 7

Answer №4

Here's the solution I came up with for pitching shifting notes. If anyone has suggestions on how to improve it, I'd love to hear them!

export function adjustPitch(
  noteItem: Note,
  direction: ShiftDirection
): Note {
  if (validateInput(noteItem, direction)) {
    return noteItem;
  }

  const newNote = transposeNote(noteItem, direction);
  const newOctave = transposeOctave(noteItem, direction);

  return { note: newNote, octave: newOctave };
}

const transposeNote = (
  noteItem: Note,
  direction: ShiftDirection
): MusicalNote => {
  const { note } = noteItem;
  if (note === 'G#' && direction === 'up') return 'A';
  if (note === 'A' && direction === 'down') return 'G#';

  const index = allNotes.indexOf(note);
  if (direction === 'up') return allNotes[index + 1];
  return allNotes[index - 1];
};

const transposeOctave = (
  noteItem: Note,
  direction: ShiftDirection
): Octave => {
  const { note, octave } = noteItem;
  if (note === 'B' && direction === 'up') {
    return (octave + 1) as Octave;
  }
  if (note === 'C' && direction === 'down') {
    return (octave - 1) as Octave;
  }
  return octave;
};

const validateInput = (
  noteItem: Note,
  direction: ShiftDirection
): boolean => {
  const { note, octave } = noteItem;
  if (note === 'A' && octave === 0 && direction === 'down') {
    console.warn('Note is already at the lowest in the register!');
    return true;
  }
  if (note === 'G#' && octave === 7 && direction === 'up') {
    console.warn('Note is already at the highest in the register!');
    return true;
  }
  return false;
};

Reference constants and types:

type MusicalNote = (typeof allNotes)[number];
type Octave = 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7;

interface Note {
  note: MusicalNote;
  octave: Octave;
}

type ShiftDirection = 'up' | 'down';
const allNotes = [ 'A', 'A#', 'B', 'C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#'] as const;

Answer 8

Here's the solution I came up with for pitching shifting notes. If anyone has suggestions on how to improve it, I'd love to hear them!

export function adjustPitch(
  noteItem: Note,
  direction: ShiftDirection
): Note {
  if (validateInput(noteItem, direction)) {
    return noteItem;
  }

  const newNote = transposeNote(noteItem, direction);
  const newOctave = transposeOctave(noteItem, direction);

  return { note: newNote, octave: newOctave };
}

const transposeNote = (
  noteItem: Note,
  direction: ShiftDirection
): MusicalNote => {
  const { note } = noteItem;
  if (note === 'G#' && direction === 'up') return 'A';
  if (note === 'A' && direction === 'down') return 'G#';

  const index = allNotes.indexOf(note);
  if (direction === 'up') return allNotes[index + 1];
  return allNotes[index - 1];
};

const transposeOctave = (
  noteItem: Note,
  direction: ShiftDirection
): Octave => {
  const { note, octave } = noteItem;
  if (note === 'B' && direction === 'up') {
    return (octave + 1) as Octave;
  }
  if (note === 'C' && direction === 'down') {
    return (octave - 1) as Octave;
  }
  return octave;
};

const validateInput = (
  noteItem: Note,
  direction: ShiftDirection
): boolean => {
  const { note, octave } = noteItem;
  if (note === 'A' && octave === 0 && direction === 'down') {
    console.warn('Note is already at the lowest in the register!');
    return true;
  }
  if (note === 'G#' && octave === 7 && direction === 'up') {
    console.warn('Note is already at the highest in the register!');
    return true;
  }
  return false;
};

Reference constants and types:

type MusicalNote = (typeof allNotes)[number];
type Octave = 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7;

interface Note {
  note: MusicalNote;
  octave: Octave;
}

type ShiftDirection = 'up' | 'down';
const allNotes = [ 'A', 'A#', 'B', 'C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#'] as const;

What is the best way to create a function that shifts a musical note up or down by one semitone?

Answer №1

Answer №2

Answer №3

Answer №4

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