## 3 Artificial Audio Effect Technologies
### Digital Signal Processing  
With computer technology becoming cheaper and more powerful towards the 1990s, it took an increasingly prominent role in music production. Indeed, the computer is the centre of the modern music production studio today and most recording and editing tasks are performed within a digital audio workstation (DAW), with digital audio effects as an important factor in contemporary music production. Computer-based DAWs are often modelled after the principle of multitrack tape recorders, emulating the established principles of the analogue recording studio. The components of the traditional recording studio, such as mixers and effects, are replaced by digital signal processing (DSP) implementations. Software synthesisers can replace external hardware synthesisers, in which case the signal can be recorded within the computer system omitting the analog-to-digital conversion step. Many DAWs feature virtual effect racks for real-time digital audio effects. Effect implementations often come in the form of _plug-ins_ that can be integrated in different host DAWs to be applied on a given track. This considerably grows the opportunities for analogue emulation and modelling. The DAW, with its easily accessible and powerful digital audio effects, continues the trend that started with the emergence of multitrack recording: the traditional role of the audio engineer and producer has been the recording of performers and subsequent mastering. [PERSON] [118] argues that, in the latter processes, engineers are part of the creative process through their mixing decisions, such as which instruments are predominant, where the instruments are placed in the stereo field, the clarity and masking of different instruments, and the audio effect modifications of those instruments. Therefore, the studio itself became a compositional tool [64,119]. Producers such as [PERSON], [PERSON], and [PERSON], who worked with several successful bands in the second half of the 20 th century, are especially noted for their innovations in the field [120,121]. The lines between producer, composer, and performer became increasingly blurred, and today, these roles may indeed be filled by a single person. This trend intensified with the emergence of music genres such as disco and sampling-based hip hop followed by popular electronic music genres and was further made possible by the decreasing cost of high-quality recording technology. This exceeds the role of enhancing the sound in a postproduction scenario. For further discussion of this phenomenon, the reader is referred to the literature, for instance [122, 123, 124, 125]. An extensive study on the methodologies and workflows of professional music producers and an analysis of the abstraction mechanisms in digital music production systems is investigated in Reference [126]. While the emulation of established analogue devices in the digital domain remains an active field of research, the majority of digital audio effects rely on signal processing principles and existing audio effects developed in the analogue domain. Digital signal processing technology makes it possible to design effects with greater complexity and precision [8]. For instance, effects based on analysis/synthesis techniques can be applied in real time, such as the phase vocoder [127] and noise removal [128]. A novel effect introduced in the late 20 th century to mention is the _auto-tune_ effect, the automatic pitch and intonation correction of the singing voice. The effect algorithm uses an auto-correlation function to determine the instantaneous pitch of an input signal and changes its pitch according to given scale [129]. This effect is another example of both transsectorial innovation and the widespread misappropriation of audio effects. The effect's inventor [PERSON] devised the auto-tune algorithm based on his work in seismic data processing for the oil industry, recognising the shared technologies of music and geophysical applications, such as correlation, linear predictive coding, and formant analysis [130].