Audio signal processing

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"Audio effect" redirects here. For special sounds used in media, see Sound effect. For a device that processes sound, see Effects unit.

Audio signal processing, sometimes referred to as audio processing, is the intentional alteration of auditory signals, or sound, often through an audio effect or effects unit. As audio signals may be electronically represented in either digital or analog format, signal processing may occur in either domain. Analog processors operate directly on the electrical signal, while digital processors operate mathematically on the digital representation of that signal.


Audio signals are sound waveslongitudinal waves which travel through air, consisting of compressions and rarefactions. These audio signals are measured in bels or in decibels. Audio processing was necessary for early radio broadcasting, as there were many problems with studio to transmitter links.[1]

Analog signals[edit]

"Analog" indicates something that is mathematically represented by a set of continuous values; for example, the analog clock uses constantly moving hands on a physical clock face, where moving the hands directly alters the information that clock is providing. Thus, an analog signal is one represented by a continuous stream of data, in this case along an electrical circuit in the form of voltage, current or charge changes (compare with digital signals below). Analog signal processing (ASP) then involves physically altering the continuous signal by changing the voltage or current or charge via various electrical means.

Historically, before the advent of widespread digital technology, ASP was the only method by which to manipulate a signal. Since that time, as computers and software became more advanced, digital signal processing has become the method of choice.

Digital signals[edit]

A digital representation expresses the pressure wave-form as a sequence of symbols, usually binary numbers. This permits signal processing using digital circuits such as microprocessors and computers. 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.[2]

Application areas[edit]

Processing methods and application areas include storage, level compression, data compression, transmission, enhancement (e.g., equalization, filtering, noise cancellation, echo or reverb removal or addition, etc.)

Audio broadcasting[edit]

Traditionally the most important audio processing (in audio broadcasting) takes place just before the transmitter. Studio audio processing is limited in the modern era due to digital audio systems ( mixers, routers) being pervasive in the studio.

In audio broadcasting, the audio processor must

  • prevent overmodulation, and minimize it when it occurs
  • compensate for non-linear transmitters, more common with medium wave and shortwave broadcasting
  • adjust overall loudness to desired level
  • correct errors in audio levels


Audio unprocessed by reverb and delay is metaphorically referred to as "dry", while processed audio is referred to as "wet".[3]

  • overdrive effects such as the use of a fuzz box can be used to produce distorted sounds, such as for imitating robotic voices or to simulate distorted radiotelephone traffic (e.g., the radio chatter between starfighter pilots in the science fiction film Star Wars)[citation needed]. The most basic overdrive effect involves clipping the signal when its absolute value exceeds a certain threshold.
  • time stretching - the complement of pitch shift, that is, the process of changing the speed of an audio signal without affecting its pitch.
  • resonators - emphasize harmonic frequency content on specified frequencies. These may be created from parametric EQs or from delay-based comb-filters.
  • 3D audio effects - place sounds outside the stereo basis
  • reverse echo - a swelling effect created by reversing an audio signal and recording echo and/or delay while the signal runs in reverse. When played back forward the last echos are heard before the effected sound creating a rush like swell preceding and during playback. Jimmy Page of Led Zeppelin used this effect in the bridge of "Whole Lotta Love".[citation needed]
  • active noise control- a method for reducing unwanted sound
  • wave field synthesis - a spatial audio rendering technique for the creation of virtual acoustic environments

See also[edit]


  1. ^ Atti, Andreas Spanias, Ted Painter, Venkatraman (2006). Audio signal processing and coding ([Online-Ausg.] ed.). Hoboken, NJ: John Wiley & Sons. p. 464. ISBN 0-471-79147-4. 
  2. ^ Zölzer, Udo (1997). Digital Audio Signal Processing. John Wiley and Sons. ISBN 0-471-97226-6. 
  3. ^ Hodgson, Jay (2010). Understanding Records, p.95. ISBN 978-1-4411-5607-5.

Further reading[edit]