{{unreferenced|date=August 2006}}
'''Audio signal processing''', sometimes referred to as '''audio processing''', is the processing of a representation of [[sound|auditory]] [[Signal (information theory)|signals]], or [[sound]]. The representation can be [[digital]] or [[analog signal|analog]].

The focus in audio signal processing is most typically a mathematical analysis of which parts of the signal are audible. For example, a signal can be modified for different purposes such that the modification is controlled in the auditory domain.

The parts of the signal are heard and which are not, is not decided merely by [[physiology]] of the [[human]] [[hearing (sense)|hearing]] system, but very much by [[psychological]] properties. These properties are analysed within the field of [[psychoacoustics]].

== History of audio processing ==
Audio processing was necessary for early [[radio broadcasting]] -- as there were many problems with studio to transmitter links.

== Analog signals ==
An analog representation is usually electrical; a [[voltage]] level represents the [[air pressure]] [[waveform]] of the sound.

== Digital signals ==
A digital representation expresses the pressure wave-form as a sequence of symbols, usually [[Binary numeral system|binary]] numbers, which permits [[digital signal processing]]. It must be noted that all real world audio signals are continuous-time and continuous-level analog signals. However, as the frequency range of audio sound sources is limited by physical effects and human ears cannot perceive frequencies below approx. {{nowrap|20 Hz}} and above approx. {{nowrap|18 kHz}} (strongly depends on the age of the listener) there is no significant loss of information when the analog signal is sampled using a high appropriate sampling rate (see: [[sampling (signal processing)|sampling]]). In addition, the dynamic range of audio signals is limited by [[Noise (sound)]]. More than {{nowrap|130 dB}} [[Signal-to-noise ratio]] is almost impossible to achieve. Therefore, [[quantization (signal processing)|quantization]] also does not result in significant loss of information either, if done appropriately.
Both, [[sampling (signal processing)|sampling]] and [[quantization (sound processing)|quantization]] must be applied to convert the continuous-time analog signal to a discrete-time digital representation. Although such a conversion is more or less lossy, 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.

== Application areas ==

Processing methods and application areas include [[audio storage|storage]], [[audio level compression|level compression]], [[audio data compression|data compression]], [[transmission (telecom)|transmission]], enhancement (e.g., [[equalization]], [[audio filter|filtering]], [[noise cancellation]], [[Echo (phenomenon)|echo]] or [[reverb]] removal or addition, etc.)

=== Audio Broadcasting ===
Audio broadcasting (be it for [[television]] or audio broadcasting) is perhaps the biggest market segment (and user area) for audio processing products -- globally.

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
* maximize overall loudness
* compensate for non-linear transmitters, more common with [[medium wave]] and [[shortwave]] broadcasting

{{Audio broadcasting}}

{{DSP}}

[[Category:Signal processing]]
[[Category:Sound technology]]

{{telecom-stub}}

[[es:Procesamiento digital de sonido]]
[[he:עיבוד אותות קול]]
[[ja:音響信号処理]]
[[nn:Audiosignalhandsaming]]
[[th:การประมวลผลสัญญาณเสียง]]