## 1 Introduction  
In this article, we describe the history of audio effects with regards to musical composition (music performance and production). We define audio effects as _the controlled transformation of a sound typically based on some control parameters_. As such, the term _sound transformation_ can be considered synonymous with _audio effect_. We focus on audio effects that are used for manipulation of recorded or performed sound, as opposed to signal processing techniques in the context of sound synthesis; that is, we take the view of an audio engineer or producer and discuss what is commonly referred to as audio effects in a music production studio. Thus, we will not specifically discuss synthesis, sound generation methods, or musical instruments. Audio effects are essential tools in contemporary music production and composition. They are applied to enhance the perceived quality of an audio signal or for creative sound design and music composition. To achieve this, sound transformations alter one or more of perceptual attributes, such as loudness, time or rhythm, pitch, timbre, and spatialisation [1, 2]. Control values determine the behaviour of the audio effect, which may be set by the user via a graphical user interface (GUI). A basic flowchart of an audio effect is shown in Figure 1.  
Figure 1: An audio effect and its control. We structure our article by specific technological innovations which gave rise to new inventions in the field of audio effects, highlighting the role of _transsectorial innovation_[3], i.e., the transfer of technology from one industrial sector to another, in the development of new audio effect techniques and music technology in general. [PERSON] [4] discusses this phenomenon with regard to the impact of digital technology on the musical instrument and audio industries, whereas [PERSON] [5] discusses music amplification technology and the crucial role that innovations in the fields of telephone, radio, and film technology have played in its development. [PERSON] [6] argues that many innovations in audio effects stem from diverting music performance and recording technology, i.e., using the technology for purposes not originally intended. The main technological advances, crucial for innovation in the development of audio effects, are identified as electromechanics (which includes analogue recording technology such as magnetic tape), analogue signal processing, digital signal processing, as well as later developments in computer science and technology such as music information retrieval and machine learning. In order to put artificial sound modification in a wider historical context, we start by discussing architectural acoustics as part of musical composition and performance prior to the age of audio recording. An exhaustive description of the large number of available audio effects and their technical specifications is out of scope for this article; however, we give examples of implementations of significant technical innovations and refer the reader to further literature where appropriate. There are several books covering the implementation of audio effects, along with some historical background [7; 8; 9; 10; 11]. Articles giving detailed overviews of specific audio effects can be found in the literature; for instance, the history of artificial reverberation is described in References [12; 13] and equalisation is discussed in References [14; 15]. [PERSON] [16] outlines the history of electronic sound modification and analogue signal processing, largely focussing on sound manipulation in the context of sound synthesis. He concludes that many of the technological principles can be \"traced back to the very early days of experimentation and that many of them have survived all phases of the technological evolution\".