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  2. Piano key frequencies - Wikipedia

    en.wikipedia.org/wiki/Piano_key_frequencies

    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.

  3. A440 (pitch standard) - Wikipedia

    en.wikipedia.org/wiki/A440_(pitch_standard)

    A440 (also known as Stuttgart pitch [1]) is the musical pitch corresponding to an audio frequency of 440 Hz, which serves as a tuning standard for the musical note of A above middle C, or A 4 in scientific pitch notation. It is standardized by the International Organization for Standardization as ISO 16.

  4. Smith chart - Wikipedia

    en.wikipedia.org/wiki/Smith_chart

    The Smith chart (sometimes also called Smith diagram, Mizuhashi chart (水橋チャート), Mizuhashi–Smith chart (水橋スミスチャート), [1] [2] [3] Volpert–Smith chart (Диаграмма Вольперта—Смита) [4] [5] or Mizuhashi–Volpert–Smith chart) is a graphical calculator or nomogram designed for electrical and electronics engineers specializing in radio ...

  5. MIDI tuning standard - Wikipedia

    en.wikipedia.org/wiki/MIDI_Tuning_Standard

    Not only is 440 Hz the standard central pitch for MIDI, it is also widely used as the "concert A " standard pitch (A 4 e.g. USA, UK), and since that is represented in MIDI signals by the integer 69 (nine semitones above middle C (C 4, c′), which is 60 decimal or 0x3C hexadecimal), this gives a real number which expresses pitch in a manner ...

  6. Electric power conversion - Wikipedia

    en.wikipedia.org/wiki/Electric_power_conversion

    In North America and northern South America, it is usually 120 volts, 60 hertz (Hz), but in Europe, Asia, Africa, and many other parts of the world, it is usually 230 volts, 50 Hz. [2] Aircraft often use 400 Hz power internally, so 50 Hz or 60 Hz to 400 Hz frequency conversion is needed for use in the ground power unit used to power the ...

  7. Bark scale - Wikipedia

    en.wikipedia.org/wiki/Bark_scale

    A440 Play ⓘ. 440 Hz = 4.21 or 4.39. The Bark scale is a psychoacoustical scale proposed by Eberhard Zwicker in 1961. It is named after Heinrich Barkhausen, who proposed the first subjective measurements of loudness. [1] One definition of the term is "a frequency scale on which equal distances correspond with perceptually equal distances.

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    mail.aol.com

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  9. Radio frequency - Wikipedia

    en.wikipedia.org/wiki/Radio_frequency

    Electric currents that oscillate at radio frequencies (RF currents) have special properties not shared by direct current or lower audio frequency alternating current, such as the 50 or 60 Hz current used in electrical power distribution. Energy from RF currents in conductors can radiate into space as electromagnetic waves (radio waves). [2]