The application of active noise or vibration control to a real situation is usually a great challenge. The step from computer simulations, or even lab studies, to the actual implementation is often much larger than first expected. This is especially true for multiple-error, multiple-output control, in which careful planning and a very great deal of preparatory work is crucial to the success of the project. The present paper is the first in a series of two, that treat the process of preparing and evaluating an active noise control system. Part I gives a general discussion on proposed methods from a theoretical standpoint. Part II describes the application of these methods in practical measurements in an aircraft application. The emphasis is on multiple-error, multiple-output control but the general guidelines haves proven to be useful even in small applications. The discussion covers some acoustical aspects as well as the signal processing view. A method, based on simulated annealing using the metropolis sampler is suggested for searching the suboptimal positions for the control sources and sensors, including a thorough discussion on the preparation of input data for the optimisation process. Finally, a version of the complex lms algorithm, normalised individually for each actuator, is discussed.