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Discrete Cosine Transform
A discrete cosine transform (DCT) expresses a finite sequence of data points in terms of a sum of cosine functions oscillating at different frequency, frequencies. The DCT, first proposed by Nasir Ahmed (engineer), Nasir Ahmed in 1972, is a widely used transformation technique in signal processing and data compression. It is used in most digital media, including digital images (such as JPEG and HEIF), digital video (such as MPEG and ), digital audio (such as Dolby Digital, MP3 and Advanced Audio Coding, AAC), digital television (such as SDTV, HDTV and Video on demand, VOD), digital radio (such as AAC+ and DAB+), and speech coding (such as AAC-LD, Siren (codec), Siren and Opus (audio format), Opus). DCTs are also important to numerous other applications in science and engineering, such as digital signal processing, telecommunication devices, reducing network bandwidth usage, and spectral methods for the numerical solution of partial differential equations. A DCT is a List of Fourier ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Data Points
In statistics, a unit of observation is the unit described by the data that one analyzes. A study may treat groups as a unit of observation with a country as the unit of analysis, drawing conclusions on group characteristics from data collected at the national level. For example, in a study of the demand for money, the unit of observation might be chosen as the individual, with different observations (data points) for a given point in time differing as to which individual they refer to; or the unit of observation might be the country, with different observations differing only in regard to the country they refer to. Unit of observation vs unit of analysis The unit of observation should not be confused with the unit of analysis. A study may have a differing unit of observation and unit of analysis: for example, in community research, the research design may collect data at the individual level of observation but the level of analysis might be at the neighborhood level, drawing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
HDTV
High-definition television (HDTV) describes a television or video system which provides a substantially higher image resolution than the previous generation of technologies. The term has been used since at least 1933; in more recent times, it refers to the generation following standard-definition television (SDTV). It is the standard video format used in most broadcasts: Terrestrial television, terrestrial broadcast television, cable television, satellite television. Formats HDTV may be transmitted in various formats: * 720p (): 921,600 pixels * 1080i () interlaced scan: 1,036,800 pixels (≈1.04Mpx). * 1080p () progressive scan: 2,073,600 pixels (≈2.07Mpx). ** Some countries also use a non-standard CTA resolution, such as : 777,600 pixels (≈0.78Mpx) per field or 1,555,200 pixels (≈1.56Mpx) per frame When transmitted at two megapixels per frame, HDTV provides about five times as many pixels as SD (standard-definition television). The increased resolution provides for a cl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spectral Method
Spectral methods are a class of techniques used in applied mathematics and scientific computing to numerically solve certain differential equations. The idea is to write the solution of the differential equation as a sum of certain " basis functions" (for example, as a Fourier series which is a sum of sinusoids) and then to choose the coefficients in the sum in order to satisfy the differential equation as well as possible. Spectral methods and finite-element methods are closely related and built on the same ideas; the main difference between them is that spectral methods use basis functions that are generally nonzero over the whole domain, while finite element methods use basis functions that are nonzero only on small subdomains (compact support). Consequently, spectral methods connect variables ''globally'' while finite elements do so ''locally''. Partially for this reason, spectral methods have excellent error properties, with the so-called "exponential convergence" being the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Network Bandwidth
In computing, bandwidth is the maximum rate of data transfer across a given path. Bandwidth may be characterized as network bandwidth, data bandwidth, or digital bandwidth. This definition of ''bandwidth'' is in contrast to the field of signal processing, wireless communications, modem data transmission, digital communications, and electronics, in which ''bandwidth'' is used to refer to the signal bandwidth measured in hertz, meaning the frequency range between lowest and highest attainable frequency while meeting a well-defined impairment level in signal power. The actual bit rate that can be achieved depends not only on the signal bandwidth but also on the noise on the channel. Network capacity The term ''bandwidth'' sometimes defines the net bit rate ''peak bit rate'', ''information rate'', or physical layer ''useful bit rate'', channel capacity, or the maximum throughput of a logical or physical communication path in a digital communication system. For example, bandwidt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telecommunication
Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of transmission may be divided into communication channels for multiplexing, allowing for a single medium to transmit several concurrent Session (computer science), communication sessions. Long-distance technologies invented during the 20th and 21st centuries generally use electric power, and include the electrical telegraph, telegraph, telephone, television, and radio. Early telecommunication networks used metal wires as the medium for transmitting signals. These networks were used for telegraphy and telephony for many decades. In the first decade of the 20th century, a revolution in wireless communication began with breakthroughs including those made in radio communications by Guglielmo Marconi, who won the 1909 Nobel Prize in Physics. Othe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Digital Signal Processing
Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The digital signals processed in this manner are a sequence of numbers that represent Sampling (signal processing), samples of a continuous variable in a domain such as time, space, or frequency. In digital electronics, a digital signal is represented as a pulse train, which is typically generated by the switching of a transistor. Digital signal processing and analog signal processing are subfields of signal processing. DSP applications include Audio signal processing, audio and speech processing, sonar, radar and other sensor array processing, spectral density estimation, statistical signal processing, digital image processing, data compression, video coding, audio coding, image compression, signal processing for telecommunications, control systems, biomedical engineering, and seismology ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Science And Engineering
Engineering is the practice of using natural science, mathematics, and the engineering design process to solve problems within technology, increase efficiency and productivity, and improve systems. Modern engineering comprises many subfields which include designing and improving infrastructure, machinery, vehicles, electronics, materials, and energy systems. The discipline of engineering encompasses a broad range of more specialized fields of engineering, each with a more specific emphasis for applications of mathematics and science. See glossary of engineering. The word ''engineering'' is derived from the Latin . Definition The American Engineers' Council for Professional Development (the predecessor of the Accreditation Board for Engineering and Technology aka ABET) has defined "engineering" as: History Engineering has existed since ancient times, when humans devised inventions such as the wedge, lever, wheel and pulley, etc. The term ''engineering'' is derived f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Opus (audio Format)
Opus is a Lossy audio compression, lossy audio coding format developed by the Xiph.Org Foundation and standardized by the Internet Engineering Task Force, designed to efficiently speech coding, code speech and general audio in a single format, while remaining latency (audio), low-latency enough for real-time interactive communication and low-complexity enough for low-end embedded processors. Opus replaces both Vorbis and Speex for new applications. Opus combines the speech-oriented Linear predictive coding, LPC-based SILK algorithm and the lower-latency Modified discrete cosine transform, MDCT-based CELT algorithm, switching between or combining them as needed for maximal efficiency. Bitrate, audio bandwidth, complexity, and algorithm can all be adjusted seamlessly in each frame. Opus has the low algorithmic delay (26.5 ms by default) necessary for use as part of a real-time communication link, networked music performances, and live lip sync; by trading off quality or bitrat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Siren (codec)
Siren is a family of patented, transform-based, wideband audio coding formats and their audio codec implementations developed and licensed by PictureTel Corporation (acquired by Polycom, Inc. in 2001). There are three Siren codecs: Siren 7, Siren 14 and Siren 22. Editions Siren 7 (or Siren7 or simply Siren) provides 7 kHz audio, bit rates 16, 24, 32 kbit/s and sampling frequency 16 kHz. Siren is derived from PictureTel's PT716plus algorithm. In 1999, ITU-T approved G.722.1 recommendation, which is based on Siren 7 algorithm. It was approved after a four-year selection process involving extensive testing. G.722.1 provides only bit rates 24 and 32 kbit/s and does not support Siren 7's bit rate 16 kbit/s. The algorithm of Siren 7 is identical to its successor, G.722.1, although the data formats are slightly different. Siren 14 (or Siren14) provides 14 kHz audio, bit rates 24, 32, 48 kbit/s for mono, 48, 64, 96 kbit/s for stereo and samplin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
AAC-LD
The MPEG-4 Low Delay Audio Coder (a.k.a. AAC Low Delay, or AAC-LD) is audio compression standard designed to combine the advantages of perceptual audio coding with the low delay necessary for two-way communication. It is closely derived from the MPEG-2 Advanced Audio Coding (AAC) standard. It was published in MPEG-4 Audio Version 2 (ISO/ IEC 14496-3:1999/Amd 1:2000) and in its later revisions. AAC-LD uses a version of the modified discrete cosine transform (MDCT) audio coding technique called the LD-MDCT. AAC-LD is widely used by Apple as the voice-over-IP (VoIP) speech codec in FaceTime. Real time CODEC requirements The most stringent requirements are a maximum algorithmic delay of only 20 ms and a good audio quality for all kind of audio signals including speech and music. * The AAC-LD coding scheme bridges the gap between speech coding schemes and high quality audio coding schemes. Two-way communication with AAC-LD is possible on usual analog telephone lines and via I ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Speech Coding
Speech coding is an application of data compression to digital audio signals containing speech. Speech coding uses speech-specific parameter estimation using audio signal processing techniques to model the speech signal, combined with generic data compression algorithms to represent the resulting modeled parameters in a compact bitstream. Common applications of speech coding are mobile telephony and voice over IP (VoIP). The most widely used speech coding technique in mobile telephony is linear predictive coding (LPC), while the most widely used in VoIP applications are the LPC and modified discrete cosine transform (MDCT) techniques. The techniques employed in speech coding are similar to those used in audio data compression and audio coding where appreciation of psychoacoustics is used to transmit only data that is relevant to the human auditory system. For example, in voiceband speech coding, only information in the frequency band 400 to 3500 Hz is transmitted but the re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DAB+
Digital Audio Broadcasting (DAB) is a digital radio international standard, standard for broadcasting digital audio radio services in many countries around the world, defined, supported, marketed and promoted by the WorldDAB organisation. The standard is dominant in Europe and is also used in Australia, and in parts of Africa and as of 2025, countries using DAB/DMB, 55 countries are actively running DAB broadcasts as an alternative platform to analogue FM. DAB was the result of a European research project and first publicly rolled out in 1995, with consumer-grade DAB Radio receiver, receivers appearing at the start of this millennium. Initially it was expected in many countries that existing FM broadcasting, FM services would switch over to DAB, although the take-up of DAB has been much slower than expected. In 2023, Norway became the first country to have implemented a national FM radio switch-off, with others to follow in the next years, Switzerland and the United Kingdom ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
