A large number of methods for pitch determination has been proposed in the literature on speech processing. Unfortunately, no single method is totally reliable over a wide range of conditions. In this paper, we propose a cooperative approach where two different methods are applied to the same signal, and their outputs are combined using a fuzzy combination operator to form a "consensus" answer. We detail our fusion technique, and discuss why fuzzy logic is an adequate tool in our case. We also present experimental results showing that our technique provides improved reliability on a wider range of situations. Keywords Speech processing, signal processing, multi-source fusion, fuzzy combination, cooperation. To appear in: World Congress of the International Fuzzy Systems Association (IFSA '97). y Supported by the Belon project, founded by the Communaut'e Fran¸caise de Belgique. z Collaborateur scientifique --- FNRS. 1 Introduction Automatic extraction of acoustic cues plays a k..