An analog or analogue signal is any continuous signal for which the time varying feature ( variable ) of the signal is a representation of some other time varying quantity, i. e., analogous to another time varying signal.

For example, in an analog audio signal, the instantaneous voltage of the signal varies continuously with the pressure of the sound waves.

The term analog signal usually refers to electrical signals ; however, mechanical, pneumatic, hydraulic, and other systems may also convey analog signals.

An analog signal uses some property of the medium to convey the signal's information.

Any information may be conveyed by an analog signal ; often such a signal is a measured response to changes in physical phenomena, such as sound, light, temperature, position, or pressure.

The physical variable is converted to an analog signal by a transducer.

An analog signal has a theoretically infinite resolution.

In practice an analog signal is subject to electronic noise and distortion introduced by communication channels and signal processing operations, which can progressively degrade the signal-to-noise ratio.

Converting an analog signal to digital form introduces a constant low-level noise called quantization noise into the signal which determines the noise floor, but once in digital form the signal can in general be processed or transmitted without introducing additional noise or distortion.

Therefore as analog signal processing systems become more complex, they may ultimately degrade signal resolution to such an extent that their performance is surpassed by digital systems.

The main advantage is the fine definition of the analog signal which has the potential for an infinite amount of signal resolution.

An analog signal may be processed directly by analog components, though some processes aren't available except in digital form.

Even if the resolution of an analog signal is higher than a comparable digital signal, the difference can be overshadowed by the noise in the signal.

Another advantage with analog signals is that their processing may be achieved more simply than with the digital equivalent.

As audio signals may be electronically represented in either digital or analog format, signal processing may occur in either domain.

Most DJ mixers now include a beat-counter which analyzes the tempo of an incoming sound source and displays its tempo in Beats Per Minute ( BPM ), which may assist with beatmatching analog sound sources.

For analog signals, signal processing may involve the amplification and filtering of audio signals for audio equipment or the modulation and demodulation of signals for telecommunications.

These days analog circuitry may use digital or even microprocessor techniques to improve performance.

Sometimes it may be difficult to differentiate between analog and digital circuits as they have elements of both linear and non-linear operation.

Defects in the original analog signal will be faithfully recorded, but may be identified and removed by a subsequent step.

While data reduction ( compression, be it lossy or lossless ) is a main goal of transform coding, it also allows other goals: one may represent data more accurately for the original amount of space – for example, in principle, if one starts with an analog or high-resolution digital master, an MP3 file of a given size should provide a better representation than a raw uncompressed audio in WAV or AIFF file of the same size.

Base analog such as 5-bromouracil may substitute for thymine in replication.

Since processors are built to interpret and process digital data, i. e. 1s and 0s, they are not able to do anything with the analog signals that may be sent to it by a device.

If successful, these effort could usher in a new era of neural computing that is a step beyond digital computing, because it depends on learning rather than programming and because it is fundamentally analog rather than digital even though the first instantiations may in fact be with CMOS digital devices.

PLCs may include logic for single-variable feedback analog control loop, a " proportional, integral, derivative " or " PID controller ".

Chips are also tested again after packaging, as the bond wires may be missing, or analog performance may be altered by the package.

Electromagnetic data may be stored in either an analog or digital format on a variety of media.

General purpose analog voltmeters may have an accuracy of a few percent of full scale, and are used with voltages from a fraction of a volt to several thousand volts.

In telecommunications and signal processing, an analog time division multiplexer ( TDM ) may take several samples of separate analogue signals and combine them into one pulse amplitude modulated ( PAM ) wide-band analogue signal.

The advantages of a digital instrument are higher precision and accuracy, but factors such as power consumption or cost may still favor application of analog meter movements.

Although digital setting circles can be used to display a telescope's RA and Dec coordinates, they are not simply a digital read-out of what can be seen on the telescope's analog setting circles.

The voltage or the current is said to be an " analog " of the sound.

Although such a conversion can be prone to loss, most modern audio systems use this approach as the techniques of digital signal processing are much more powerful and efficient than analog domain signal processing.

Short of actually playing a sound in the desired environment, the effect of echo can be implemented using either digital or analog methods.

Analog ( or analogue ) television is the analog transmission that involves the broadcasting of encoded analog audio and analog video signal: one in which the information to be transmitted, the brightness and colors of the points in the image and the sound waves of the audio signal are represented by continuous variations of some aspect of the signal ; its amplitude, frequency or phase.

When analog television was developed, no affordable technology for storing any video signals existed ; the luminance signal has to be generated and transmitted at the same time at which it is displayed on the CRT.

The development of transistors made electronic analog computers practical, and until digital computers had developed sufficiently, they continued to be commonly used in science and industry.

Setting up an analog computer required scale factors to be chosen, along with initial conditions — that is, starting values.

The design of the analog joystick, which used a weak rubber boot rather than springs to provide centering, proved to be ungainly and unreliable.

Similarly, the total mass inside a sphere containing a black hole can be found by using the gravitational analog of Gauss's law, the ADM mass, far away from the black hole.

Computation can be classified by at least three orthogonal criteria: digital versus analog, sequential versus parallel versus concurrent, batch versus interactive.

Due to widespread cable theft in earlier analog systems, in modern digital cable systems the signals are encrypted, and the set-top box must be activated by an activation code sent by the cable company before it will function, which is only sent after the subscriber signs up.

One of the standards available for digital cable telephony, PacketCable, seems to be the most promising and able to work with the Quality of Service ( QOS ) demands of traditional analog Plain old telephone service ( POTS ) service.

The biggest advantage to digital cable telephone service is similar to the advantage of digital cable TV, namely that data can be compressed, resulting in much less bandwidth used than a dedicated analog circuit-switched service.

If the data to be compressed is analog ( such as a voltage that varies with time ),