Frequency

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Examples

• The frequency of the standard pitch A above middle C is usually defined as 440 Hz, that is, 440 cycles per second ({{Audio|Media:440Hz.ogg|Listen}}) and known as concert pitch, to which an orchestra tunes.
• A baby can hear tones with oscillations up to approximately 20,000 Hz, but these frequencies become more difficult to hear as people age.
• In Europe, the frequency of the alternating current in mains is 50 Hz (close to the tone G).
• In North America, the frequency of the alternating current is 60 Hz (close to the tone B flat ? that is, a minor third above the European frequency). The frequency of the 'hum' in an audio recording can show where the recording was done ? in Europe or in America.