All Topics  
Sampling rate

 

 
   Email Print
   Bookmark   Link
 

 

Sampling rate
 
 
  Topics Sampling rate Topic Home

The sampling rate, sample rate, or sampling frequency defines the number of samples per second
Second

The second , sometimes abbreviated sec., is the name of a units of measurement of time, and is the International System of Units SI base unit of time....
 (or per other unit) taken from a continuous signal
Continuous signal

A continuous signal or a continuous-time signal is a varying quantity that is expressed as a function of a real-valued domain, usually time....
 to make a discrete signal
Discrete signal

A discrete signal or discrete-time signal is a time series, perhaps a signal that has been sampling from a continuous signal.Unlike a continuous-time signal, a discrete-time signal is not a function of a continuous-time argument, but is a sequence of quantities; that is, a function over a Domain of discrete integers....
. For time-domain signals, it can be measured in hertz
Hertz

The hertz is a measure of frequency per unit of time, or the number of list of cycles per second. It is the SI base unit of frequency in the International System of Units , and is used worldwide in both general-purpose and scientific contexts....
 (Hz). The inverse of the sampling frequency is the sampling period or sampling interval, which is the time between samples.

The concept of sampling frequency can only be applied to sampler
Sampling (signal processing)

In signal processing, sampling is the reduction of a continuous signal to a discrete signal. A common example is the conversion of a sound wave to a sequence of sample ....
s in which samples are taken periodically.






Discussion
Ask a question about 'Sampling rate'
Start a new discussion about 'Sampling rate'
Answer questions from other users
Full Discussion Forum



Encyclopedia


The sampling rate, sample rate, or sampling frequency defines the number of samples per second
Second

The second , sometimes abbreviated sec., is the name of a units of measurement of time, and is the International System of Units SI base unit of time....
 (or per other unit) taken from a continuous signal
Continuous signal

A continuous signal or a continuous-time signal is a varying quantity that is expressed as a function of a real-valued domain, usually time....
 to make a discrete signal
Discrete signal

A discrete signal or discrete-time signal is a time series, perhaps a signal that has been sampling from a continuous signal.Unlike a continuous-time signal, a discrete-time signal is not a function of a continuous-time argument, but is a sequence of quantities; that is, a function over a Domain of discrete integers....
. For time-domain signals, it can be measured in hertz
Hertz

The hertz is a measure of frequency per unit of time, or the number of list of cycles per second. It is the SI base unit of frequency in the International System of Units , and is used worldwide in both general-purpose and scientific contexts....
 (Hz). The inverse of the sampling frequency is the sampling period or sampling interval, which is the time between samples.

The concept of sampling frequency can only be applied to sampler
Sampling (signal processing)

In signal processing, sampling is the reduction of a continuous signal to a discrete signal. A common example is the conversion of a sound wave to a sequence of sample ....
s in which samples are taken periodically. Some samplers may sample at a non-periodic rate.

The common notation for sampling frequency is which stands for frequency (subscript) sampled.

Sampling theorem


The Nyquist–Shannon sampling theorem
Nyquist–Shannon sampling theorem

The Nyquist?Shannon sampling theorem is a fundamental result in the field of information theory, in particular telecommunications and signal processing....
 states that perfect reconstruction of a signal is possible when the sampling frequency is greater than twice the maximum frequency of the signal being sampled, or equivalently, when the Nyquist frequency
Nyquist frequency

The Nyquist frequency, named after the Swedish-American engineer Harry Nyquist or the Nyquist?Shannon sampling theorem, is half the sampling frequency of a discrete signal processing system....
 (half the sample rate) exceeds the highest frequency of the signal being sampled. If lower sampling rates are used, the original signal's information may not be completely recoverable from the sampled signal.

For example, if a signal has an upper band limit of 100 Hz, a sampling frequency greater than 200 Hz will avoid aliasing
Aliasing

In statistics, signal processing, computer graphics and related disciplines, aliasing refers to an effect that causes different continuous signals to become indistinguishable when sampling ....
 and allow theoretically perfect reconstruction.

Oversampling


In some cases, it is desirable to have a sampling frequency considerably more than twice the desired system bandwidth so that a digital filter
Digital filter

In electronics, computer science and mathematics, a digital filter is a system that performs mathematical operations on a Sampling , discrete-time Signal to reduce or enhance certain aspects of that signal....
 can be used in exchange for a weaker analog anti-aliasing filter
Anti-aliasing filter

An anti-aliasing filter is a filter used before a signal sampler, to restrict the bandwidth of a signal to approximately satisfy the Nyquist?Shannon sampling theorem....
. This process is known as oversampling
Oversampling

In signal processing, oversampling is the process of sampling a signal with a sampling frequency significantly higher than twice the Bandwidth or highest frequency of the signal being sampled....
.

Video systems


In digital video
Digital video

Digital video is a type of video recording system that works by using a digital rather than an analog signal video signal.The terms camera, video camera, and camcorder are used interchangeably in this article....
, the temporal sampling rate is defined the frame/field rate, rather than the notional pixel clock. The image sampling frequency is the repetition rate of the sensor integration period. Since the integration period may be significantly shorter than the time between repetitions, the sampling frequency can be different from the inverse of the sample time.
  • 50 Hz - PAL
    PAL

    PAL, short for Phase Alternating Line, is a color-encoding system used in broadcast television systems in large parts of the world. Other common analog television systems are SECAM and NTSC....
     video
  • 60 / 1.001 Hz - NTSC
    NTSC

    NTSC is the analog television system used in most of the Americas, Japan, South Korea, Taiwan, the Philippines, Burma, and some Pacific island nations and territories ....
     video


When analog video is converted to digital video
Digital video

Digital video is a type of video recording system that works by using a digital rather than an analog signal video signal.The terms camera, video camera, and camcorder are used interchangeably in this article....
, a different sampling process occurs, this time at the pixel frequency, corresponding to a spatial sampling rate along scan line
Scan line

A scan line is one line, or row, in a raster scanning pattern, such as a line on a cathode ray tube display of a television or computer.On older CRT screens the horizontal scan lines were visually discernible, even when viewed from a distance, as alternating colored lines and black lines....
s. Some common pixel
Pixel

In digital imaging, a pixel is the smallest item of information in an image. Pixels are normally arranged in a 2-dimensional grid, and are often represented using dots, squares, or rectangles....
 sampling rates are:
  • 13.5 MHz - CCIR 601
    CCIR 601

    ITU-R Recommendation BT.601, more commonly known by the abbreviations Rec. 601 or BT.601 is a standard published by ITU-R for encoding interlaced analogue video signals in digital form....
    , D1 video
Spatial sampling in the other direction is determined by the spacing of scan lines in the raster
Raster

Raster may refer to:* Raster graphics, graphical techniques using arrays of pixel values* Raster scan, the pattern of image readout, transmission, storage, and reconstruction in television and computer images...
. The sampling rates and resolutions in both spatial directions can be measured in units of lines per picture height.

Spatial aliasing
Aliasing

In statistics, signal processing, computer graphics and related disciplines, aliasing refers to an effect that causes different continuous signals to become indistinguishable when sampling ....
 of high-frequency luma
Luma (video)

As applied to video signals, luma represents the brightness in an image . Luma is typically paired with Chrominance. Luma represents the achromatic image without any color, while the chroma components represent the color information....
 or chroma
Chrominance

Chrominance , is the signal used in video systems to convey the color information of the picture, separately from the accompanying luma signal....
 video components shows up as a moiré pattern
Moiré pattern

In physics, a moir? pattern is an interference pattern created, for example, when two grids are overlaid at an angle, or when they have slightly different mesh sizes....
.

See also


  • Digital control
    Digital control

    Digital control is a branch of control theory that uses digital computers to act as system controllers.Depending on the requirements, a digital control system can take the form of a microcontroller to an Application-specific integrated circuit to a standard desktop computer....
  • Sample and hold
    Sample and hold

    In electronics, a sample and hold circuit is used to interface real-world signals, by changing analog signal signals to a subsequent system such as an analog-to-digital converter....
  • Sample rate conversion
    Sample rate conversion

    Sample rate conversion is the process of converting a signal from one sampling rate to another, while changing the information carried by the signal as little as possible....
  • Signal (information theory)
  • Bit rate