Audio Effect Units in Mobile Devices for Electric Musical Instruments

With the advent of modern techniques, there has been an increase in mobile devices with powerful functions. This study aims to utilize application software instead of hardware equipment to alter the sound of electric musical instruments by developing the functions of audio effect units on a mobile device. The built-in software audio effects include dynamic effects, delay effects, mixing, and equalization. Multichannel audio signal processing is proposed to enhance sound externalization. The listening tests indicate that the sound effects together with a quadraphonic system produce superior special effects and spatial audio than conventional effect units. Additionally, a denoiser is proposed for noise reduction, which is a function especially helpful for singers performing on busy streets. The customization in the module is achieved by a personal voice preprocessing system. A dual-filter function was utilized for the denoiser to adjust to different environments. The objective performance measurements demonstrate that the proposed denoiser outperforms the state-of-the-art methods. A hardware audio interface serving as the connection between a mobile device and an electric instrument, such as an electric guitar, electric piano, or electric bass, was also built, providing impedance matching and voltage balance. The proposed interface transfers the electric instrument signal into a 3.5-mm jack in a smartphone or tablet. The developed audio interface is light and low-noise and can operate without being connected to an external power supply, thereby making it suitable for street musicians. The experiments validate the feasibility of using the proposed circuit for real-time audio signal conversion.