33 1/3 is a slow speed for a record, and 78 rpm is a fast speed, so saying his voice sounded like a 78 rpm record turned down to 33 1/3 would mean it sounded slow, not fast
Consider the statement "His voice sounded incredibly fast and energetic". Based on this "His voice sounded like a 78-rpm record turned down to 33 1/3." a true statement? Yes, no, or I don't know?