Say ta. Say da. Now repeat the sounds, in each case paying attention to how you’re making them in your mouth. What’s the difference?
Trick question! There isn’t one. It’s not what’s happening in your mouth that makes these sounds different. It’s the “voice onset time”—the time between when you start moving your tongue and when you start vibrating your vocal cords. If that time is greater than roughly 40 milliseconds, English-speakers will hear ta. If it’s less than 40 milliseconds, they’ll hear da. Read this brilliant HBR article to find out more!