Understanding Musical Notes and Octaves

When using a tuner, you’ll see notes labeled like “A4,” “E2,” or “C5.” What do these letters and numbers mean? This guide explains the musical note system, from the basic scale to octave numbering, and why the note “A” became the universal tuning reference.

The Musical Alphabet

The Seven Notes

Western music is built on seven natural notes, named with the first seven letters of the alphabet:

After B, the pattern repeats starting from C again. This creates a continuous cycle of notes.

Why Does It Start with C, Not A?

You might wonder: if we use the alphabet, why doesn’t the scale start with A?

Historically, the note names came from medieval music theory. The lowest note in the commonly used range of early chants was labeled “A.” As music theory evolved, the scale beginning on C (the “C major scale”) became the most fundamental scale because it contains no sharps or flats—it’s the “white keys only” scale on a piano.

So while the alphabet starts at A, the most basic musical scale starts at C. The note A remains important as the tuning reference, which we’ll discuss later.

Sharps and Flats

Between some natural notes, there are additional notes called sharps (♯) and flats (♭):

This gives us 12 unique pitches (the chromatic scale), which repeat in higher and lower octaves.

What Is an Octave?

The 2:1 Frequency Ratio

An octave is the interval between one note and the next note with the same name. Physically, when you go up one octave, the frequency exactly doubles.

This 2:1 ratio is why notes an octave apart sound “the same but higher” or “the same but lower.” Our ears perceive them as fundamentally related.

Why “Octave”?

The word “octave” comes from Latin “octavus” meaning “eighth.” In a major scale (do-re-mi-fa-sol-la-si-do), the eighth note is the same as the first, just higher—that’s one octave.

Octave Numbering: Scientific Pitch Notation

The Modern Standard

Scientific Pitch Notation (SPN) combines the note name with an octave number. This system was standardized by the Acoustical Society of America in 1939.

Key reference points:

• C4 = “Middle C” (261.63 Hz) — the C near the middle of a piano
• A4 = 440 Hz — the international tuning standard
• A0 = 27.5 Hz — the lowest A on a standard piano
• C8 = 4186 Hz — the highest C on a standard piano

The Complete Piano Range

A standard 88-key piano spans from A0 to C8:

Why Does Octave 4 Start at C, Not A?

In Scientific Pitch Notation, each octave starts at C and ends at B. So the sequence is:

… → A3 → B3 → C4 → D4 → E4 → F4 → G4 → A4 → B4 → C5 → …

This means A4 (440 Hz) is actually in the upper part of octave 4, not at the beginning.

Why Is “A” the Tuning Reference?

Historical Reasons

Several factors made A the natural choice for a tuning reference:

1. Position in the scale: A is in the middle of the musical alphabet, making it a neutral central reference point

2. String instruments: Many string instruments have an open A string that’s easy to tune and hear clearly

3. Orchestral tradition: When orchestras tune, the oboe plays an A, and other instruments match it. The oboe was chosen because its pitch is stable and penetrating

4. Vocal range: A4 (440 Hz) sits comfortably in the range where the human ear is most sensitive

The Math of A = 440 Hz

When A4 equals exactly 440 Hz, it creates convenient numbers for many other pitches using equal temperament:

The frequency of any note can be calculated using the formula:

f = 440 × 2^((n-69)/12)

Where n is the MIDI note number (A4 = 69).

Different Naming Systems

Fixed vs. Movable Do

There are two main approaches to solfège:

Fixed Do (used in most of Europe, Asia):

• C is always “Do,” regardless of the key
• A is always “La”
• Used for absolute pitch reference

Movable Do (used in UK, US, and for education):

• “Do” is the first note of whatever scale you’re in
• If you’re in G major, G is “Do”
• Used for understanding relative relationships

Letter Names vs. Solfège

*In German notation, B♭ is called “B” and B natural is called “H.”

Practical Applications

Reading a Tuner

When your tuner shows “E2”:

• E = the note name
• 2 = the octave number
• This is the low E string on a guitar (82.41 Hz)

When your tuner shows “A4”:

• A = the note name
• 4 = the octave number
• This is the standard tuning reference (440 Hz)

Understanding Instrument Ranges

Knowing the octave system helps you understand instrument ranges:

Quick Reference

The Complete Chromatic Scale in Octave 4

Key Points to Remember

1. Seven natural notes: C-D-E-F-G-A-B (then repeats)
2. Twelve total pitches: Including sharps/flats
3. Octave = frequency ×2: A3 (220 Hz) → A4 (440 Hz)
4. Middle C = C4: The center of the piano
5. A4 = 440 Hz: The international tuning standard

Related Articles

• History of A440 - Why 440Hz became the standard
• Standard Tuning Frequencies - Complete frequency reference
• How to Use the Chromatic Tuner - Tune accurately to any note
• String Numbering Systems - Understanding string numbers

Now that you understand musical notes and octaves, learn more about why A4 = 440 Hz became the international standard!