The term 'stereo predecessor' refers to the two technologies that preceded stereo sound. The first is 'mono, ' which stands for monophonic sound, and was the first type of sound recording technology. Mono recordings were made with a single microphone and reproduced through a single speaker. The second is 'HiFi, ' which stands for high fidelity, and was the first type of sound reproduction technology to use multiple channels. HiFi recordings used multiple microphones and speakers to create a more realistic sound.