The span between two sounds can be infinite, but some of them cannot be heard by human ears, such as ultrasonic waves and infrasound waves. As for musical instruments, the piano has the largest span, with 88 tones. A common acoustic guitar can generally play 37 notes.
The audible sound frequency range of the human ear: 20Hz (Hertz) ~ 20000Hz (Hertz), that is, the number of air vibrations per second can be heard by the human ear between 20 and 20,000 times, and the number of vibrations per second is less than Less than 20 times per second are called infrasound waves, and more than 20,000 times per second are called ultrasonic waves.
The frequency of middle c is C4: 261.62557 Hz, and the frequency between each two notes on the piano changes according to (A4: 440 Hz).
When calculated according to the twelve equal laws and taking the A above the middle C as 440 Hz, the frequency of the middle C is about 261.6 Hz.
So why is a1 440 Hz? In fact, it has not always been...
Before the tuning fork was invented, determining the standard pitch was a very troublesome matter. In an era when the church organ was the main standard, the same note could differ by as much as five degrees.
From Purcell to Beethoven, including Bach and Mozart, the pitch of a1 is approximately between 415 and 429 Hz, which is called classical pitch;
During the Romantic period, bright tone was advocated, and a1 was raised to about 455 Hz;
In 1834, the German Physicists Association in Stuttgart stipulated that a1=440 Hz;
The pitch of the London Philharmonic Society The standard once reached a1=452 Hz;
In 1880, the most famous Steinway piano in Europe and the United States was tuned with a1=457 Hz.
France set a1 = 435 Hz as the legal standard for implementation in 1859. In 1885, the Vienna International Conference designated it as the "international pitch";
The 1939 London Conference decided Resume the results of the Stuttgart Conference.
Today, a1=440 Hz is called the "First International Pitch", and a1=435 Hz is called the "Second International Pitch".