Pitch: choose how high a note sounds

Pitch is how high or low a sound feels. A bass note is low; a whistle is high. Volume is a separate choice: making a note louder does not raise its pitch.

Start with the sound basics. To run the examples, install Tono, then save Rust code as src/main.rs and run cargo run, or save Python code as pitch.py and run python pitch.py.

Hz, note names, and octaves

Hertz (Hz) counts vibrations per second. More Hz means a higher pitch. A note name gives that pitch a musical label: A4 is 440 Hz. The letter names the note; the number names its octave, or pitch register.

Note	Frequency	What you hear
A3	220 Hz	Lower A
A4	440 Hz	The reference A
A#4	About 466.16 Hz	One small step above A4
A5	880 Hz	A4 raised one octave

An octave contains 12 semitones. A semitone is the small step from A4 to A#4; moving up 12 semitones doubles the frequency. Moving down an octave halves it. The note keeps its letter, but sounds in a higher or lower register.

Create a note and move it

Create A4, then move it up one semitone and one octave. Both examples print:

A4: MIDI 69, 440.00 Hz
A#4: MIDI 70, 466.16 Hz
A5: MIDI 81, 880.00 Hz

MIDI here is simply a numbered note: adding 1 moves up one semitone. It does not require a keyboard or a MIDI device.

Rust

use tono_core::music::Pitch;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let a = Pitch::from_name("A4")?;
    let notes = [a, a.add_semitones(1)?, a.add_semitones(12)?];
    for pitch in notes {
        println!("{pitch}: MIDI {}, {:.2} Hz", pitch.to_midi(), pitch.to_hz());
    }
    Ok(())
}

Python

import tono

a = tono.Pitch("A4")
notes = [a, a.transpose(1), a.transpose(12)]
for pitch in notes:
    # Python exposes MIDI; this converts that number to Hz.
    hz = 440 * 2 ** ((pitch.midi - 69) / 12)
    print(f"{pitch.name}: MIDI {pitch.midi}, {hz:.2f} Hz")

For note spelling, use a letter A–G, an optional # (sharp) or b (flat), and an octave: C4, F#3, Gb5. A sharp raises the plain note one semitone; a flat lowers it one. F#4 and Gb4 name the same pitch; Tono displays it as F#4. s also works for sharp (Fs4), and midi:60 names C4.

The Pitch API requires the octave and accepts only one accidental. C, H4, and C##4 fail with an error; it does not guess what you meant. Use plain # and b, rather than the musical symbols ♯ and ♭.

Turn four notes into a phrase

A phrase is a short musical idea. This one plays C4, E4, G4, C5 in order on a piano, one note per beat. At 120 beats per minute, each beat lasts half a second.

Rust

use tono_core::prelude::*;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let octave_shift = 0; // Try 12 to raise the whole phrase one octave.
    let mut notes = Vec::new();
    for (beat, name) in ["C4", "E4", "G4", "C5"].iter().enumerate() {
        let pitch = Pitch::from_name(name)?.add_semitones(octave_shift)?;
        println!("{pitch}");
        notes.push(note(beat as u32 * 4, 4, &pitch.to_string()));
    }
    let mut song = Song::new("climb", 120.0);
    song.add_voice("piano", &GrandPiano::grand());
    song.add_pattern("climb", 1, notes);
    song.arrange("piano", "climb", 0);
    let program = song.compile(&CompileOptions {
        sample_rate: Some(48_000), ..Default::default()
    })?;
    let (left, _right) = program.render_stereo();
    println!("Rendered {} stereo frames", left.len());
    Ok(())
}

Python

import tono

octave_shift = 0  # Try 12 to raise the whole phrase one octave.
phrase = tono.Pattern(bars=1)
for beat, name in enumerate(["C4", "E4", "G4", "C5"]):
    pitch = tono.Pitch(name).transpose(octave_shift)
    print(pitch.name)
    phrase.note(pitch.name, at=beat, duration=1)
song = tono.Song("climb", tempo=120)
piano = song.track("piano", tono.instruments.piano())
song.arrange(piano, phrase, bars=0)
program = song.compile(sample_rate=48_000)
audio = program.render()
print(f"Rendered {len(audio)} stereo frames")

Both render 192,000 stereo frames in memory: two seconds of notes plus the compiler’s two-second tail allowance. They do not open speakers. Follow the WAV example to save a file you can hear.

Change octave_shift to 12: the phrase becomes C5, E5, G5, C6. Every pitch doubles in frequency; the rhythm and chosen instrument stay the same. Change it to -12 for a lower version. To change the character of the sound, choose a different instrument.

Next: tempo and rhythm — decide when notes play and how long they last.