question: On which recording types were pre-emphasis used most in the 1920s ?
answer: 78 rpm and 33 1⁄3 rpm
turker_answer: Pre-emphasis were used most in the 1920s on the recording types 78 rpm and 33 1⁄3 rpm .
rule-based: Pre-emphasis were used most in the 1920s on 78 rpm and 33 1⁄3 rpm .