Changes

*4. ''Physics'': The [[process]] of modulating an [[electromagnetic]] [[wave]] or other oscillating signal, or a beam, esp. in order to impress a signal on it; the extent to which a modulated carrier wave is varied; the modulated waveform or signal itself.  

*4. ''Physics'': The [[process]] of modulating an [[electromagnetic]] [[wave]] or other oscillating signal, or a beam, esp. in order to impress a signal on it; the extent to which a modulated carrier wave is varied; the modulated waveform or signal itself.  

==Description==

==Description==

In [http://en.wikipedia.org/wiki/Electronics electronics], '''modulation''' is the [[process]] of varying one or more properties of a high [[frequency]] periodic [http://en.wikipedia.org/wiki/Waveform waveform], called the ''carrier signal'', with respect to a modulating signal. This is done in a similar [[fashion]] as a musician may modulate a [[tone]] (a periodic [waveform) from a musical instrument by varying its [[volume]], [[timing]] and [[pitch]]. The three key [[parameters]] of a periodic waveform are its [http://en.wikipedia.org/wiki/Amplitude amplitude] ("volume"), its [http://en.wikipedia.org/wiki/Phase_(waves) phase] ("timing") and its [http://en.wikipedia.org/wiki/Frequency frequency] ("pitch"), all of which can be modified in [[accordance]] with a low frequency signal to obtain the modulated signal. Typically a [http://en.wikipedia.org/wiki/High-frequency high-frequency] [http://en.wikipedia.org/wiki/Sinusoid sinusoid] waveform is used as [http://en.wikipedia.org/wiki/Carrier_wave carrier signal], but a square wave pulse train may also occur.

In [https://en.wikipedia.org/wiki/Electronics electronics], '''modulation''' is the [[process]] of varying one or more properties of a high [[frequency]] periodic [https://en.wikipedia.org/wiki/Waveform waveform], called the ''carrier signal'', with respect to a modulating signal. This is done in a similar [[fashion]] as a musician may modulate a [[tone]] (a periodic [waveform) from a musical instrument by varying its [[volume]], [[timing]] and [[pitch]]. The three key [[parameters]] of a periodic waveform are its [https://en.wikipedia.org/wiki/Amplitude amplitude] ("volume"), its [https://en.wikipedia.org/wiki/Phase_(waves) phase] ("timing") and its [https://en.wikipedia.org/wiki/Frequency frequency] ("pitch"), all of which can be modified in [[accordance]] with a low frequency signal to obtain the modulated signal. Typically a [https://en.wikipedia.org/wiki/High-frequency high-frequency] [https://en.wikipedia.org/wiki/Sinusoid sinusoid] waveform is used as [https://en.wikipedia.org/wiki/Carrier_wave carrier signal], but a square wave pulse train may also occur.

In [http://en.wikipedia.org/wiki/Telecommunications telecommunications], modulation is the [[process]] of conveying a [[message]] signal, for example a digital bit stream or an analog audio signal, inside another signal that can be [[physically]] [[transmitted]]. Modulation of a sine waveform is used to transform a [http://en.wikipedia.org/wiki/Baseband baseband] message signal to a [http://en.wikipedia.org/wiki/Passband passband] signal, for example a [http://en.wikipedia.org/wiki/Radio radio]-frequency signal (RF signal). In radio communications, cable TV systems or the [http://en.wikipedia.org/wiki/Public_switched_telephone_network public switched telephone network] for instance, [[electrical]] signals can only be [[transferred]] over a limited passband frequency [[spectrum]], with specific (non-zero) lower and upper cutoff frequencies. Modulating a sine wave carrier makes it possible to keep the frequency content of the transferred signal as close as possible to the centre frequency (typically the carrier frequency) of the passband. When coupled with [http://en.wikipedia.org/wiki/Demodulation demodulation], this [[technique]] can be used to, among other things, [[transmit]] a signal through a [[channel]] which may be [[opaque]] to the baseband frequency range (for instance, when sending a telephone signal through a [http://en.wikipedia.org/wiki/Optical_fiber fiber-optic] strand).

In [https://en.wikipedia.org/wiki/Telecommunications telecommunications], modulation is the [[process]] of conveying a [[message]] signal, for example a digital bit stream or an analog audio signal, inside another signal that can be [[physically]] [[transmitted]]. Modulation of a sine waveform is used to transform a [https://en.wikipedia.org/wiki/Baseband baseband] message signal to a [https://en.wikipedia.org/wiki/Passband passband] signal, for example a [https://en.wikipedia.org/wiki/Radio radio]-frequency signal (RF signal). In radio communications, cable TV systems or the [https://en.wikipedia.org/wiki/Public_switched_telephone_network public switched telephone network] for instance, [[electrical]] signals can only be [[transferred]] over a limited passband frequency [[spectrum]], with specific (non-zero) lower and upper cutoff frequencies. Modulating a sine wave carrier makes it possible to keep the frequency content of the transferred signal as close as possible to the centre frequency (typically the carrier frequency) of the passband. When coupled with [https://en.wikipedia.org/wiki/Demodulation demodulation], this [[technique]] can be used to, among other things, [[transmit]] a signal through a [[channel]] which may be [[opaque]] to the baseband frequency range (for instance, when sending a telephone signal through a [https://en.wikipedia.org/wiki/Optical_fiber fiber-optic] strand).

In music synthesizers, modulation may be used to synthesise waveforms with a desired overtone [[spectrum]]. In this case the carrier frequency is typically in the same order or much lower than the modulating waveform. See for example [http://en.wikipedia.org/wiki/Frequency_modulation_synthesis frequency modulation synthesis] or ring modulation.

In music synthesizers, modulation may be used to synthesise waveforms with a desired overtone [[spectrum]]. In this case the carrier frequency is typically in the same order or much lower than the modulating waveform. See for example [https://en.wikipedia.org/wiki/Frequency_modulation_synthesis frequency modulation synthesis] or ring modulation.

A device that [[performs]] modulation is known as a modulator and a device that performs the inverse operation of modulation is known as a [http://en.wikipedia.org/wiki/Demodulator demodulator] (sometimes detector or demod). A device that can do both operations is a [http://en.wikipedia.org/wiki/Modem modem] (short for "Modulator-Demodulator").[http://en.wikipedia.org/wiki/Modulation]

A device that [[performs]] modulation is known as a modulator and a device that performs the inverse operation of modulation is known as a [https://en.wikipedia.org/wiki/Demodulator demodulator] (sometimes detector or demod). A device that can do both operations is a [https://en.wikipedia.org/wiki/Modem modem] (short for "Modulator-Demodulator").[https://en.wikipedia.org/wiki/Modulation]

[[Category: Physics]]

[[Category: Physics]]