Abstract. Optical music recognition (OMR) enables librarians to digitise early music sources on a large scale. The cost of expert human labour to correct automatic recognition errors dominates the cost of such projects. To reduce the number of recognition errors in the OMR process, we present an innovative approach to adapt the system dynamically, taking advantage of the human editing work that is part of any digitisation project. The corrected data are used to perform MAP adaptation, a machine-learning technique used previously in speech recognition and optical character recognition (OCR). Our experiments show that this technique can reduce editing costs by more than half. 1 Background Indexing music sources for intelligent retrieval is currently a laborious process that requires highly skilled human editors [1]. Optical music recognition (OMR), the musical analogue to optical character recognition (OCR), can speed this process and greatly reduce the labour cost. In the case of early ...