Realization of a Digitally Controlled Analog Delay Effect

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Firtha Gergely
Department of Networked Systems and Services

This thesis presents various methods for producing a time-delayed version of an audio signal, which is a popular musical effect across many genres. Such effect can be achieved with the use of analog circuitry containing Bucket Brigade Device (BBD) integrated circuits. I discuss the history, different topologies and uses of these devices, along with their important characteristics and limitations, including aliasing, distortion and noise. To reduce these artifacts BBDs are often accompanied by low-pass filters and compander circuitry. This produces unique sonic characteristics that are preferred by many musicians, but these analog devices unfortunately lack many useful functions offered by digital systems. During my work I used a schematic based on the Boss DM-2 guitar pedal, to realize an analog delay effect with three adjustable parameters: Time, Feedback and Mix. In my thesis I present a microcontroller based digital circuit and software for controlling the effect’s parameters along with the advantages and possibilities of using such digital control. I also discuss the design considerations for producing a printed circuit board and present a possible board layout designed with the Eagle CAD software. Based on measurements, I verified that the effect is functioning as expected and also discuss some of the unique characteristics of BBD delay effects,


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