Differences between analog signal and digital signal are given below :
• Analog signal is a continuous signal whereas Digital signal is discrete time signal.
• Analog signal is denoted by sin waves whereas Digital signal is denoted by square waves.
• Analog signal has high noise whereas Digital signal has less noise.
• Analog signal is stored in the form of wave signal whereas Digital signal is stored in the form of binary bit.
• Analog signal has less cost whereas Digital signal has high cost.
• Analog signal example is - Human voice whereas Digital signal example is Computer system.

HDMI Encoder Modulator,16in1 Digital Headend,HD RF Modulator at SOUKA https://www.soukacatv.com/.

Purely digital signals exist as a sequence of samples. These samples might be stored somewhere or digitally processed. They are both discrete in time and quantized in amplitude.

Analog signals are the physical signals that propagate through some medium i.e. a circuit, cable, the air, etc. They are continuous in both time and amplitude.

The reason I started by talking about “purely” digital signals is because that’s really an abstraction. The reality is that everything in this world is analog. When we talk about a digital circuit which reads/writes a byte of data, the reality is that the circuit operates on analog inputs and outputs. But by intelligently designing the circuit we can abstract away these details and just think about the digital signals. A wireless transmission that contains digital information still ultimately uses an analog signal to propagate through the air.

Analog signal: (continues signals )
1.analog signal is continues signals which represents physical measurements .
2.wave : denoted by sine wave
3. Example : Human voice in air, analog electronic devices.
4.Representation:Uses continuous range of values to represent information
5.Data transmissions :Subjected to deterioration by noise during transmission and write/read cycle.
6. Uses : Can be used in analog devices only. Best suited for audio and video transmission.

Digital Signals
1.Digital signals are discrete time signals generated by digital modulation.
2.wave : denoted by square wave
3.Examples :Computers, CDs, DVDs, and other digital electronic devices.
4. Representation: Uses discrete or discontinuous values to represent information
5.Data Transmission: Can be noise-immune without deterioration during transmission and write/read cycle.
6.Uses :Best suited for Computing and digital electronic.

The following graph is more clear in understanding there signals..

Main difference you get between analog and digital signals is that analog real time Signals and digital signals that are performed within the system it's basically your voice my voice and everyone else's voice is analogue because suppose you are speaking a sentence you are going to spell it till the end Undertaker instead of time I can measure a certain DB of noise coming from your mouth so this noise is introduced into the transducer which converts it into voltage signals now the signals are analog in nature the main thing which we get defect is analogue parts has many losses and also the computational time is pretty high compared to the digital so we use an analogto digital converter to convert these analog signals into digital signals by the help of sampling that is we take the values of the signal at every small instant of time this small instant of time is very small and it has to follow nyquist criterion I am not going into the details of this criterion about it in the later stages but the sampling is basically we are taking the values of this signal at every small instant of time such that will get a large value of the data of the original signal. These data are converted into zeros and ones and processes in the system which are digital in nature and finally after all the computations it is converted do analog

To understand this difference, let us go back a bit and start with the very basics:
Q: What is a signal?
- A signal is a plot of the value of a physical quantity/parameter with respect to time. In other words, a signal carries information about the change in the value of a quantity/parameter over a period of time. The physical quantity could be anything that we are trying to measure, like temperature, speech, light intensity etc.

NOTE- If the physical quantity being measured is an electrical parameter, like Voltage or Current, then the signal is called an electrical signal.

- An analog signal is continuous with respect to time; meaning its value changes continuously with time. In other words, an analog signal will have a value at any given instant of time. For example, the value of an analog signal can be extracted at 0s, 1.5s, 4.908675s etc.

- All real world signals are analog in nature.

Q: What are signals used for?
- There are three things that can be done with a signal:
1.Store the signal for later use
2.Process the signal (convert it to some other form, perform some operations on the signal etc)
3.Transmit the signal to some other destination to be used there.

- Now, since analog signals are continuous, it will have infinite number of values considering the value at each instant of time. Therefore, storing such a signal requires large amount of memory; processing requires large processing power or more time; transmitting requires a large bandwidth.

Q: So, is there an easy way to handle signals?
- YES. Instead of measuring/considering the signal value at every instant of time, lets take the signal value only at desired instances of time. In other words, we consider signal "samples" at specific instances of time.

- Above picture shows an analog signal sampled at specific time instances (t1 - t10). Such a signal is called as a "discrete time signal", since the signal values are represented at discrete time units. In technical terms, the signal values are called as "samples" and this process is called as "sampling". Closer these samples are, more accurate will be the signal representation. The number of samples to be considered is determined by the "sampling rate" of the system.

- With discrete time signal, there's a problem. The amplitude of the samples can be real numbers (5.38239, 13.57236 etc) representing which may become tedious. To overcome this, just like we divided the x-axis at discrete intervals, let us also divide the y-axis at discrete intervals.

- If the signal amplitude falls between 0 and L1, let us round it off to 0. If the signal amplitude falls between L1 and L2, we round it off to L1 and so on. Again, the closer these levels are, more accurate will be the signal representation.

- This process is called as "quantization" and the resulting quantized signal is called a "Digital Signal".

- Most digital systems today make use of only two signal levels, Level0 and Level1.

- These signal levels have different names in the world of digital electronics;

Level0 or Logic0/OFF/False/Absent
Level1 or Logic1/ON/True/Present

- That is, at any given instant of time the signal is either present or it is absent. If it is present, we call it Logic1, or simply 1, and if it is absent we call it Logic0, or simply 0.

- Analog signals are converted into digital signals, processed in digital form and converted back to analog on need basis, because it is easier to handle/work with digital signals.

- we cannot completely do away with analog signals, so at the earliest possible time we take the analog signal and if the signal is very weak, we amplify it to a desirable level and convert it into a digital signal.

Let me try to answer your question in most easiest way. In text book B.P. Lathi of analog and digital communication system, signals are defined of four types based on which axis (time or amplitude) is sampled:
1. Continuous time and continuous amplitude signal: this type of signal is continuous in both axis and neither of the axis is sampled. These type of signals are also called analog signal.
2. Continuous time and discrete amplitude signal: As name suggests, these signals are continuous in time but discrete in amplitude i.e. signal is sampled in amplitude only.
3. Discrete time and continuous amplitude signal: These signals are sampled only on time axis and amplitude is continuous. These signals are also most commonly called just discrete signals.
4. Discrete time and discrete amplitude signal: These signals are sampled in both axises i.e. both time and amplitude axises are sampled. These signals are also called digital signals.

If you have understood all above 4 definitions, then by now you can understand the difference between analog and digital signal. In analog signal both the axises are continuous whereas in digital signals, both the axises are sampled or discrete.

Analog signal is a continuous signal with infinite time and magnitude resolution. Real world signals are analog signals, sound, light, radio waves, etc. Take that real world signal and digitize it with discrete time steps and finite magnitude resolution, you get digital signals. Sound file and digital pictures are examples of digital signal.
The key concept for converting between digital and analog signals is the sampling theorem. In simple terms, a signal digitized at twice the highest frequency content of an analog signal can be perfectly reconverted back to analog. For example, we deem 8kHz sampling rate is good enough to cover the highest pitch female voice, whereas 44kHz was acceptable for CD recording of a piece of music. However, there are always some outliers who can or claim they can hear well about 22kHz tones.

Digital audio is technology that can be used to record, store, generate, manipulate, and reproduce sound using audio signals that have been encoded in digital form. Following significant advances in digital audio technology during the 1970s, it gradually replaced analog audio technology in many areas of sound production, sound recording (tape systems were replaced with digital recording systems), sound engineering and telecommunications in the 1990s and 2000s.

A microphone converts sound to an analog electrical signal, then an analog-to-digital converter (ADC)—typically using pulse-code modulation—converts the analog signal into a digital signal. This digital signal can then be recorded, edited and modified using digital audio tools. When the sound engineer wishes to listen to the recording on headphones or loudspeakers (or when a consumer wishes to listen to a digital sound file of a song), a digital-to-analog converter performs the reverse process, converting a digital signal back into an analog signal, which analog circuits amplify and send to a loudspeaker.

Digital audio systems may include compression, storage, processing and transmission components. Conversion to a digital format allows convenient manipulation, storage, transmission and retrieval of an audio signal. Unlike analog audio, in which making copies of a recording leads to degradation of the signal quality, when using digital audio, an infinite number of copies can be made without any degradation of signal quality.

Overview

Digital audio technologies in the 2010s are used in the recording, manipulation, mass-production, and distribution of sound, including recordings of songs, instrumental pieces, podcasts, sound effects, and other sounds. Modern online music distribution depends on digital recording and data compression. The availability of music as data files, rather than as physical objects, has significantly reduced the costs of distribution.

Before digital audio, the music industry distributed and sold music by selling physical copies in the form of records and cassette tapes. With digital audio and online distribution systems such as iTunes, companies sell digital sound files to consumers, which the consumer receives over the Internet. This digital audio/Internet distribution model is much less expensive than producing physical copies of recordings, packaging them and shipping them to stores.

An analog audio system captures sounds, and converts their physical waveforms into electrical representations of those waveforms by use of a transducer, such as a microphone. The sounds are then stored, as on tape, or transmitted. The process is reversed for playback: the audio signal is amplified and then converted back into physical waveforms via a loudspeaker. Analog audio retains its fundamental wave-like characteristics throughout its storage, transformation, duplication, and amplification.

Analog audio signals are susceptible to noise and distortion, due to the innate characteristics of electronic circuits and associated devices. Disturbances in a digital system do not result in error unless the disturbance is so large as to result in a symbol being misinterpreted as another symbol or disturb the sequence of symbols. It is therefore generally possible to have an entirely error-free digital audio system in which no noise or distortion is introduced between conversion to digital format, and conversion back to analog.

A digital audio signal may be encoded for correction of any errors that might occur in the storage or transmission of the signal, but this is not strictly part of the digital audio process. This technique, known as "channel coding", is essential for broadcast or recorded digital systems to maintain bit accuracy. The discrete time and level of the binary signal allow a decoder to recreate the analog signal upon replay. Eight to Fourteen Bit Modulation is a channel code used in the audio Compact Disc (CD).

Conversion process

The lifecycle of sound as it happens usually is from its source, through an ADC, digital processing, a DAC, and finally as sound again.

A digital audio system starts with an ADC that converts an analog signal to a digital signal.

The ADC runs at a specified sampling rate and converts at a known bit resolution. CD audio, for example, has a sampling rate of 44.1 kHz (44,100 samples per second), and has 16-bit resolution for each stereo channel. Analog signals that have not already been bandlimited must be passed through an anti-aliasing filter before conversion, to prevent the distortion that is caused by audio signals with frequencies higher than the Nyquist frequency, which is half of the system's sampling rate.

A digital audio signal may be stored or transmitted. Digital audio can be stored on a CD, a digital audio player, a hard drive, a USB flash drive, or any other digital data storage device. The digital signal may then be altered through digital signal processing, where it may be filtered or have effects applied. Audio data compression techniques, such as MP3, Advanced Audio Coding, Ogg Vorbis, or FLAC, are commonly employed to reduce the file size. Digital audio can be streamed to other devices.

For playback, digital audio must be converted back to an analog signal with a DAC. DACs run at a specific sampling rate and bit resolution, but may use oversampling, upsampling or downsampling to convert signals that have been encoded with a different sampling

What is the difference between analogue and digital transmission?
When we talk about analogue or digital, we are referring to the type of transmission of a signal. There are a number of key differences between analogue and digital signal transmission.

Analogue Transmission
An analogue signal (otherwise known as a wave form) is characterised by being continuously variable along both amplitude and frequency. In the case of telephony, when we speak into a handset, our voice is converted into current, or voltage fluctuations. Those fluctuations in current are an analogue transmission of the actual voice pattern.

To transmit an analogue signal effectively, we need to define the frequency in which is operates. In telephony, the usable voice frequency band ranges from approximately 300 Hz to 3400 Hz, and so the network provider (phone company) will allocate a bandwidth of around 4,000Hz for voice transmission.

Because of the limited bandwidth analogue facilities have, they cannot support high-speed data transmission.

Digital Transmission
Digital signals are much simpler than analogue signals. Instead of a continuous wave form, analogue signals are made up of a series of pulses that represent either one bit or zero bits. Each computer system uses a coding scheme which defines what combinations of ones and zeros make up all the characters in the character set.

The data (ones and zeros) are carried throughout the network depending on whether it is an electrical or optical transmission system.

Electrical
Transmitting digital signals over an electrical system essentially means that the ones are represented by high voltage and zero bits are represented as low voltage (or nothing at all).

Optical
In optical networks, the ones are represented as the presence of light and zeros as the absence of light.

Established in 2000, the Soukacatv.com (DSW) main products are modulators both in digital and analog modulators, amplifier and combiner. We are the leading communication supplier in manufacturing the headend system in China. Our 16 in 1 and 24 in 1 now are the most popular products all over the world. For more, please access to https://www.soukacatv.com/.

Source https://www.quora.com/What-is-the-difference-between-digital-signal-and-analog-signal