From Longman Dictionary of Contemporary Englishlower the tone (of something)lower the tone (of something)RUDE/IMPOLITEto make something not as nice as it was They thought an influx of students would lower the tone of the neighborhood. Trust you to lower the tone of the conversation (=include rude jokes etc in what you say)! → lower
Examples from the Corpus
lower the tone (of something)• Far from lowering the tone, the changes are set to improve it. 