STOPDUB is a made-up word that doesn't appear in any language. When we pronounce it, we can divide it into two syllables: "stop" and "dub." The consonant sound "p" represents the voiceless plosive, while "d" represents the voiced plosive. This means that when we pronounce "p," we don't use our vocal cords, but when we pronounce "d," we do. Therefore, the spelling of STOPDUB is a combination of voiceless and voiced consonant sounds, resulting in a unique pronunciation.