Thursday, April 18, 2024
HomeTechAudio signal processing

Audio signal processing

Audio signal processing is a subfield of signal processing that is concerned with the electronic manipulation of audio signals. Audio signals are electronic representations of sound waves—longitudinal waves which travel through air, consisting of compressions and rarefactions. The energy contained in audio signals is typically measured in decibels. As audio signals may be represented in either digital or analog format, processing may occur in either domain. Analog processors operate directly on the electrical signal, while digital processors operate mathematically on its digital representation.

History Audio signal processing

The motivation for audio signal processing began at the beginning of the 20th century with inventions like the telephone, phonograph, and radio that allowed for the transmission and storage of audio signals. Audio processing was necessary for early radio broadcasting, as there were many problems with studio-to-transmitter links. The theory of signal processing and its application to audio was largely developed at Bell Labs in the mid 20th century. Claude Shannon and Harry Nyquist’s early work on communication theory, sampling theory and pulse-code modulation (PCM) laid the foundations for the field. In 1957, Max Mathews became the first person to synthesize audio from a computer, giving birth to computer music.

Major developments in digital audio coding and audio data compression include differential pulse-code modulation (DPCM) by C. Chapin Cutler at Bell Labs in 1950, linear predictive coding (LPC) by Fumitada Itakura (Nagoya University) and Shuzo Saito (Nippon Telegraph and Telephone) in 1966, adaptive DPCM (ADPCM) by P. Cummiskey, Nikil S. Jayant and James L. Flanagan at Bell Labs in 1973, discrete cosine transform (DCT) coding by Nasir Ahmed, T. Natarajan and K. R. Rao in 1974, and modified discrete cosine transform (MDCT) coding by J. P. Princen, A. W. Johnson and A. B. Bradley at the University of Surrey in 1987. LPC is the basis for perceptual coding and is widely used in speech coding, while MDCT coding is widely used in modern audio coding formats such as MP3 and Advanced Audio Coding (AAC).

Analog signals

An analog audio signal is a continuous signal represented by an electrical voltage or current that is analogous to the sound waves in the air. Analog signal processing then involves physically altering the continuous signal by changing the voltage or current or charge via electrical circuits.

Historically, before the advent of widespread digital technology, analog was the only method by which to manipulate a signal. Since that time, as computers and software have become more capable and affordable, digital signal processing has become the method of choice. However, in music applications, analog technology is often still desirable as it often produces nonlinear responses that are difficult to replicate with digital filters.

Digital signals

A digital representation expresses the audio waveform as a sequence of symbols, usually binary numbers. This permits signal processing using digital circuits such as digital signal processors, microprocessors and general-purpose computers. Most modern audio systems use a digital approach as the techniques of digital signal processing are much more powerful and efficient than analog domain signal processing.[11]

Applications

Processing methods and application areas include storage, data compression, music information retrieval, speech processing, localization, acoustic detection, transmission, noise cancellation, acoustic fingerprinting, sound recognition, synthesis, and enhancement (e.g. equalization, filtering, level compression, echo and reverb removal or addition, etc.).

Audio broadcasting

Audio signal processing is used when broadcasting audio signals in order to enhance their fidelity or optimize for bandwidth or latency. In this domain, the most important audio processing takes place just before the transmitter. The audio processor here must prevent or minimize overmodulation, compensate for non-linear transmitters (a potential issue with medium wave and shortwave broadcasting), and adjust overall loudness to desired level.

Active noise control

Active noise control is a technique designed to reduce unwanted sound. By creating a signal that is identical to the unwanted noise but with the opposite polarity, the two signals cancel out due to destructive interference.

Audio synthesis

Audio synthesis is the electronic generation of audio signals. A musical instrument that accomplishes this is called a synthesizer. Synthesizers can either imitate sounds or generate new ones. Audio synthesis is also used to generate human speech using speech synthesis.

Audio effects

Audio effects alter the sound of a musical instrument or other audio source. Common effects include distortion, often used with electric guitar in electric blues and rock music; dynamic effects such as volume pedals and compressors, which affect loudness; filters such as wah-wah pedals and graphic equalizers, which modify frequency ranges; modulation effects, such as chorus, flangers and phasers; pitch effects such as pitch shifters; and time effects, such as reverb and delay, which create echoing sounds and emulate the sound of different spaces.

Musicians, audio engineers and record producers use effects units during live performances or in the studio, typically with electric guitar, bass guitar, electronic keyboard or electric piano. While effects are most frequently used with electric or electronic instruments, they can be used with any audio source, such as acoustic instruments, drums, and vocals.

Computer audition

Computer audition (CA) or machine listening is general field of study of algorithms and systems for audio understanding by machine. Since the notion of what it means for a machine to “hear” is very broad and somewhat vague, computer audition attempts to bring together several disciplines that originally dealt with specific problems or had a concrete application in mind. The engineer Paris Smaragdis, interviewed in Technology Review, talks about these systems –“software that uses sound to locate people moving through rooms, monitor machinery for impending breakdowns, or activate traffic cameras to record accidents.”

Inspired by models of human audition, CA deals with questions of representation, transduction, grouping, use of musical knowledge and general sound semantics for the purpose of performing intelligent operations on audio and music signals by the computer. Technically this requires a combination of methods from the fields of signal processing, auditory modelling, music perception and cognition, pattern recognition, and machine learning, as well as more traditional methods of artificial intelligence for musical knowledge representation.

Follow us on Twitter. Send us a secure tip

- A word from our sponsors -

Most Popular

More from Author

Angola’s Billionaire Elite: Unveiling the Top 10 Wealthiest Moguls in 2024

Here's a look at Angola's wealthiest individuals in 2024, highlighting the...

Algeria’s Billionaire Elite: Unveiling the Top 10 Wealthiest Moguls in 2024

Algeria, with its significant oil and gas reserves, has a group...

Ethiopias’s Billionaire Elite: Unveiling the Top 10 Wealthiest Moguls in 2024

Ethiopia, known for its rich cultural heritage, is also home to...

- A word from our sponsors -

Angola’s Billionaire Elite: Unveiling the Top 10 Wealthiest Moguls in 2024

Here's a look at Angola's wealthiest individuals in 2024, highlighting the top entrepreneurs and business magnates who are shaping the country's economic landscape. This list is current for 2024 and excludes Isabel Dos Santos, focusing on the new and prevailing forces in Angola's billionaire circle.Angola’s Billionaire Elite:...

Discover the Ultimate Road Companion: Nissan Caravan Now Available in Mombasa, Kenya

Are you on the hunt for a vehicle that combines robust performance with spacious comfort? Look no further than the Nissan Caravan, currently on offer in the bustling city of Mombasa, Kenya. Ideal for businesses requiring cargo transport, groups seeking adventure, or families needing extra space, the...

Algeria’s Billionaire Elite: Unveiling the Top 10 Wealthiest Moguls in 2024

Algeria, with its significant oil and gas reserves, has a group of wealthy individuals whose influence spans across various industries including construction, manufacturing, food, and pharmaceuticals. Here is a table summarizing the top 10 wealthiest individuals in Algeria as of 2024:As of 2024, here is the latest...

Rising Icon of Sport: Kenya’s Talanta Stadium Set to Redefine African Athletics

Kenya's Pinnacle of Pride: Unveiling the Talanta Sports CityNAIROBI-KENYA | Amidst the bustling energy of Nairobi, a new landmark rises - the Talanta Sports City. A marvel of architecture that intertwines the spirit of Kenyan heritage with cutting-edge design, this stadium is poised to become a beacon...

Ethiopias’s Billionaire Elite: Unveiling the Top 10 Wealthiest Moguls in 2024

Ethiopia, known for its rich cultural heritage, is also home to some of the wealthiest individuals in Africa. These moguls have diversified their investments across various sectors including oil, mining, agriculture, and real estate, significantly contributing to the nation's economic development. Here's a look at the top...

Trailblazers of Wealth: Kenya’s Five Most Influential Women in 2024

Kenya's economic landscape is distinguished not only by its vibrant markets and industries but also by the formidable women who have risen to the top of these sectors. As of 2024, here is a detailed look at the five richest women in Kenya, highlighting their net worth,...