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This is a list of the fundamental frequencies in hertz (cycles per second) of the keys of a modern 88-key standard or 108-key extended piano in twelve-tone equal temperament, with the 49th key, the fifth A (called A 4), tuned to 440 Hz (referred to as A440). [1] [2] Every octave is made of twelve steps called semitones.
1 hertz (Hz) 1 to 1.66 Hz: Approximate frequency of an adult human's resting heart beat: 1 Hz: 60 bpm, common tempo in music 2 Hz: 120 bpm, common tempo in music ~7.83 Hz: Fundamental frequency of the Schumann resonances: 10 1: 10 hertz 10 Hz: Cyclic rate of a typical automobile engine at idle (equivalent to 600 rpm) 12 Hz
The frequency range starts at MIDI note 0, C = 8.1758 Hz, and extends above MIDI note 127, G = 12543.854 Hz. The first byte of the frequency data word specifies the highest equal-tempered semitone not exceeding the frequency. The next two bytes (14 bits) specify the fraction of 100 cents above the
MIDI note numbers shown in parentheses next to their corresponding keyboard note. MIDI allows the selection of an instrument's sounds through program change messages, but there is no guarantee that any two instruments have the same sound at a given program location. [112] Program #0 may be a piano on one instrument, or a flute on another.
The purpose of this adjustment is to move the 12 notes within a smaller range of frequency, namely within the interval between the base note D and the D above it (a note with twice its frequency). This interval is typically called the basic octave (on a piano keyboard, an octave has only 12 keys).
For example, if a piano string tuned to 440 Hz (vibrations per second) is played together with a piano string tuned to 442 Hz, the resulting tone beats at a frequency of 2 Hz, due to the constructive and destructive interference between the two sound waves.
The PC 97 standard requires that a computer's BIOS must detect and work with USB HID class keyboards that are designed to be used during the boot process. Some keyboards implement the USB Boot Keyboard profile specified in the USB Device Class Definition for Human Interface Devices (HID) v1.11 and are explicitly configured to use the boot protocol.
The keyboard sends the key code to the keyboard driver running in the main computer; if the main computer is operating, it commands the light to turn on. All the other indicator lights work in a similar way. The keyboard driver also tracks the shift, alt and control state of the keyboard.