My signature work is a mobile app aimed to help Mandarin learners improve their pronunciation skills using speech recognition and related technologies. The user can record their voice and get instant phoneme-level feedback from anywhere on earth. The app intuitively shows them which syllables they pronounced correctly and which they did not, including the tone pronunciation. To achieve these goals, I constructed an improved version of an existing Computer-Aided Pronunciation Training (CAPT) algorithm. The new system can spot common pronunciation errors made by international students at DKU and recognizes tone pronunciation accurately. I also published a paper about Mandarin tone recognition.