It isn't always. Baseband analog signals have no carrier.
An analog-to-digital converter is a device which converts an infinite resolution analog signal to a finite resolution digital signal.
An DAC convert digital signal to analog signal i.e Digital to Analog Converter. An ADC convert analog signal to digital signal i.e Analog to Digital Converter.
An analog-to-digital converter is a device which converts an infinite resolution analog signal to a finite resolution digital signal.
modem means modulator demodulator. it converts digital signal to analog signal. it is use to transmit computer signal (digital signal) over the telephone line to communicate to other computers. modem converts the computer digital signal into frequency (analog signal) so that it can transmit over the telephone line and at the receiving end the modem converts the analog signal back to digital for the receiving computer to understand it.
For transmission through a radiowave.
The most fundamental difference, I would say, is that Amplitude Modulation (AM) is a kind of Analog Modulation Technique (the modulation is applied continuously in response to the analog information signal) where Amplitude Shift Keying is a type of Digital Modulation Technique ( an analog carrier signal is modulated by a discrete signal, digital modulation methods can be considered as digital-to-analog conversion, and the corresponding demodulation or detection as analog-to-digital conversion. The changes in the carrier signal are chosen from a finite number of M alternative symbols).
Digital signal is moreefficientimmune to noiseerror freethan analog signal.
by analog to digital,digital to analog signal
In a analog transmitter the RF carrier have to be modulated with the analog signal either by AM or FM where in digital transmitter the carrier is simply switched on and off a off = a zero and on = a one
The set top box that your provider gives you is what converts the Digital signal to the analog signal. The digital signal is compressed at the provider and sent to the end user. The "tuner" (which can be built into a tv, a set top box or a cable card) Then decompresses the digital signal and converts it into an analog signal. There is much more to this did not know how technical you wanted your answer.
A modem is a modulator and demodulator device that modulates the analog carrier signal to encode the digital information and demodulates the signal to decode the transmitted information. The modem usually produces a signal that can be transmitted easily and decoded to reproduce the original data.