Singing or humming to a music search engine is an appealing multimodal interaction paradigm, particularly for small sized portable devices that are ubiquitous nowadays. The aim of this work is to overcome the main shortcoming of the existing query-by-humming (QBH) systems: their lack of scalability in terms of the difficulty of automatically extending the database of melodies from audio recordings. A method is proposed to extract the singing voice melody from polyphonic music providing the necessary information to index it as an element in the database. The search of a query pattern in the database is carried out combining note sequence matching and pitch time series alignment. A prototype system was developed and experiments are carried out pursuing a fair comparison between manual and automatic expansion of the database. In the light of the obtained performance (85% in the top-10), which is encouraging given the results reported to date, this can be considered a proof of concept that validates the approach