A method includes: loading, by a processor, a grammar specification defining at least one parameterizable grammar including a plurality of rules; setting, by the processor, an initial state of a grammar processor as a current state, the current state including parameters supplied to the rules; selecting, by the processor, a rule of the plurality of rules matching the parameters of the current state of the grammar processor; applying, by the processor, the selected rule to the audio and updating the current state; determining, by the processor, whether termination conditions have been met; in response to determining the termination conditions are not met, selecting, by the processor, from the plurality of rules in accordance with parameters of the updated state; and in response to determining the termination conditions are met, outputting, by the processor, a recognizer result of the current state.