"Trail off" is commonly used to describe a gradual decrease or diminishment of sound or speech. If you want to add some variety to your writing, there are several synonyms for this phrase. You could use "fade away," "taper off," or "die down" to convey a similar meaning. Another option is "dwindle," which implies a steady decrease over time. Additionally, "ebb" or "recede" suggest a gradual retreat or withdrawal. If you want to convey a sudden end, you could use "cease abruptly" or "fall silent." Experimenting with synonyms can make your writing more interesting and engaging.