Music Production
Convert MIDI note numbers to frequency and back.
What this calculator does
MIDI note numbers and frequency are two different ways of representing the same musical pitch—one discrete and symbolic, the other continuous and physical. MIDI (Musical Instrument Digital Interface) uses note numbers from 0-127, where each number represents a specific pitch according to the chromatic scale. Frequency measures the physical vibration rate in Hertz. Musicians and producers constantly work with both representations: synthesizers display frequency for oscillators and filters, while sequencers and keyboards use MIDI note numbers. This converter enables quick translation between the two, essential for programming synthesizers, understanding frequency-based effects parameters, mapping keyboard input to synthesis parameters, and translating between different musical and technical contexts. Understanding the mathematical relationship helps in designing modulation systems, wavetable synthesis, and frequency-dependent processing.
How it works
The converter uses the equal temperament tuning system and a reference frequency (standard A4 = MIDI note 69 = 440 Hz). Given a MIDI note number, the calculator computes how many semitones away it is from A4, then applies the formula to calculate frequency. Given a frequency, it calculates which MIDI note number is closest, showing cents deviation if the frequency doesn't fall exactly on a note. The relationship is exponential: each semitone (12 per octave) represents a frequency multiplication of 2^(1/12) ≈ 1.059. MIDI note 0 represents about 8.18 Hz (C-1, below human hearing), while note 127 represents about 12,543 Hz (G9, near the limit of human hearing).
Formula
Frequency = 440 × 2^((MIDI note - 69) / 12). Or in reverse: MIDI note = 69 + 12 × log₂(Frequency / 440). MIDI note 0 = C-1 ≈ 8.18 Hz. MIDI note 60 = C4 (middle C) ≈ 262 Hz. MIDI note 69 = A4 = 440 Hz. MIDI note 127 = G9 ≈ 12,543 Hz.
Tips for using this calculator
- Remember MIDI note 60 is middle C and 69 is A4; these are reference points for visualizing the 127-note range
- Many synthesizers allow CV (control voltage) frequency control; understanding MIDI-to-frequency mapping helps you design modulation to frequency-sensitive parameters
- Use this converter when programming wavetables or frequency modulation (FM) synthesis where precise frequency relationships matter
- In step sequencers and live performance, knowing MIDI numbers helps you quickly navigate and transpose sequences without thinking in frequencies
- Understanding the exponential nature of the scale explains why octave transposition (±12 semitones) exactly doubles or halves frequency
Frequently asked questions
What's the difference between MIDI notes and keyboard keys?
MIDI note numbers (0-127) are a continuous numeric system representing pitch. A piano keyboard has 88 keys, typically starting at MIDI note 21 (A0) and ending at MIDI note 108 (C8). Other instruments like organ have fewer keys, while MIDI allows control of the full 128-note range. When you play a key on a MIDI keyboard, it sends a MIDI note number to your synthesizer or DAW. The synthesizer then interprets that number and generates the corresponding frequency.
Why is MIDI note 69 used as the standard reference?
MIDI note 69 is A4 (440 Hz), the internationally standardized tuning reference. This choice makes A4 easy to reference in MIDI systems and ensures that standard tuning (A4 = 440 Hz) aligns with a whole MIDI note number. Using MIDI note 69 as the pivot point for frequency calculations simplifies the math compared to other reference points and is what all MIDI devices expect.
Can MIDI represent frequencies between notes?
Standard MIDI note numbers (0-127) represent discrete semitone pitches. However, MIDI pitch bend messages can modulate frequency continuously between notes with extremely fine resolution. Additionally, some synthesizers respond to MPE (MIDI Polyphonic Expression) which allows continuous pitch control per note. For maximum flexibility, many synthesizers accept CV (control voltage) input that maps directly to frequency, allowing infinite frequency precision outside the discrete MIDI note grid.
How does MIDI tuning work with non-440 Hz tuning standards?
Standard MIDI assumes A4 = 440 Hz, but some instruments or genres use alternative tunings (442 Hz for orchestral music, 432 Hz for alternative tuning enthusiasts). If your synth supports it, you can adjust the master tuning reference while keeping MIDI note numbers unchanged. Alternatively, you can transpose MIDI note numbers or use pitch bend. The frequency converter can work with any reference frequency by adjusting the baseline—it's just a mathematical relationship between MIDI note and frequency.
