For reference, in scientific pitch, A4 = 430.54 Hz (assuming equal temperament tuning ratios). This system is not commonly used today the now globally dominant pitch tuning system is international pitch standard (A4 = 440 Hz). Scientific pitch measures C4 (“middle C”) at 256 Hz and all other Cs as powers of 2. Great question! Scientific pitch notation was originally meant to be a companion to a standardized system of tuning pitch frequencies, called “scientific pitch”. As this can get confusing, both Scientific Pitch Notation and Scientific Pitch Standard can go by additional names: The difference between them is that scientific pitch notation is a system for naming pitches, and scientific pitch is a system for tuning pitches. To summarize, Scientific Pitch Notation was created as a companion for a tuning system called scientific pitch. But if one musician uses international pitch standard and the other uses scientific pitch or Verdi tuning, and they both play A4, the A4s will sound nearly the same, but slightly out of tune with each other because they are vibrating at different frequencies. Why does this distinction matter? If two musicians use international pitch standard tuning, and both musicians play A4, the two A4s will sound exactly the same (a perfect blend!) because they are vibrating at the same frequency (440 Hz). A4 is still A4 whether it is tuned to 430.54 Hz, 432 Hz, 440 Hz, etc. It's important to recognize that different tuning systems change only the tuning of pitches, NOT their names. For reference, in scientific pitch, A4 = 430.54 Hz (assuming equal temperament tuning ratios), and A4 in Verdi tuning = 432 Hz. Today, the now globally dominant pitch tuning system is international pitch standard ( A4 = 440 Hz). This system was appreciated for its mathematical idealism, but it is not commonly used today.

Scientific pitch standard measures C4 ('middle C') at 256 Hz and all other Cs as powers of 2.

Every musical pitch vibrates at a unique frequency, so to help musicians play in tune with each other, various systems of standardizing pitch frequencies (like scientific pitch) have been developed over time. Pitch frequencies are how many times a sound wave vibrates per second (measured in Hertz, abbreviated Hz). Scientific pitch notation was invented to be a companion to scientific pitch standard (a system for measuring pitch frequencies). One of the commenters below asked this excellent question, so I decided to post the answer here.

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