Bede Liu, an emeritus professor of electrical engineering and a pioneer in digital signal processing, died on May 7. He was 91. Liu’s pathbreaking research aided the transition from analog to digital processing of sound, images and video. Along with the 53 Ph.D. students he mentored, he developed methods of filtering and compressing digital signals to mitigate errors and dramatically reduce the computation needed for signal processing. These techniques have led to now-ubiquitous technologies for storing and streaming media. “He was a highly impactful scholar and teacher — always thinking ahead of future needs and changing technologies,” said colleague Peter Ramadge, the Gordon Y.S. Wu Professor of Engineering, Emeritus. In the 1990s, Liu turned his attention to media integrity and copyright issues. He created techniques for digital watermarking — hidden signals that could identify a genuine copy of a song, image or video and prevent unauthorized distribution or tampering. Lessons learned from Liu's work have guided industries in identifying suitable settings and applications for watermarking. For example, each copy of a Hollywood film given to a critic or theater now carries a unique forensic watermark to prevent unauthorized redistribution, said Min Wu, a 2001 Ph.D. alumna who worked on digital watermarking with Liu. Former students and colleagues remembered Liu for his humility, humor and generosity. For Ken Steiglitz, the Eugene Higgins Professor of Computer Science, Emeritus, “cheer” is the word that first comes to mind when thinking of Liu. He was “always ready with a positive remark, a quick smile, or, maybe, some tips on the right way to cook a duck.” Liu loved to organize dinners with colleagues and students at Chinese restaurants — both in the Princeton area and when traveling for conferences, said H. Vincent Poor, the Michael Henry Strater University Professor of Electrical and Computer Engineering.