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The first such analog modulating waveforms applied to radio carriers were human voice signals picked up by microphone sensors and applied to the carrier waveforms. The resulting analog voice modes are known today as: Amplitude modulation (AM) Double-sideband suppressed carrier (DSB-SC) Independent sideband (ISB) Single sideband (SSB)
The bandwidth allocated for a single voice-frequency transmission channel is usually 4 kHz, including guard bands, [2] allowing a sampling rate of 8 kHz to be used as the basis of the pulse-code modulation system used for the digital PSTN.
In analog frequency modulation, such as radio broadcasting, of an audio signal representing voice or music, the instantaneous frequency deviation, i.e. the difference between the frequency of the carrier and its center frequency, has a functional relation to the modulating signal amplitude.
Continuously variable slope delta modulation (CVSD or CVSDM) is a voice coding method. It is a delta modulation with variable step size (i.e., special case of adaptive delta modulation), first proposed by Greefkes and Riemens in 1970. CVSD encodes at 1 bit per sample, so that audio sampled at 16 kHz is encoded at 16 kbit/s.
It is an ITU-T standard (Recommendation) for audio encoding, titled Pulse code modulation (PCM) of voice frequencies released for use in 1972. G.711 passes audio signals in the frequency band of 300–3400 Hz and samples them at the rate of 8000 Hz, with the tolerance on that rate of 50 parts per million (ppm).
As of 2012, most countries divide the upper 19 MHz into 760 channels for amplitude modulation voice transmissions, on frequencies from 118 to 136.975 MHz, in steps of 25 kHz. In Europe, it is becoming common to further divide those channels into three (8.33 kHz channel spacing), potentially permitting 2,280 channels.
In radio communications, single-sideband modulation (SSB) or single-sideband suppressed-carrier modulation (SSB-SC) is a type of modulation used to transmit information, such as an audio signal, by radio waves. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently.
Pulse-amplitude modulation: L: Pulse-width modulation (e.g. as used by WWVB) M: Pulse-position modulation: N: Unmodulated carrier (steady, single-frequency signal) P: Sequence of pulses without modulation Q: Sequence of pulses, with phase or frequency modulation in each pulse R: Single-sideband with reduced or variable carrier: V