in mandarin chinese, there are no voiced stops, fricatives, or affricates, so the only way to tell them apart is by aspiration. in pinyin, aspirated sounds are written like voiceless sounds in english, so the sounds /pʰ/, /tʰ/, and /kʰ/ are written as 'p', 't', and 'k' in the same order, but unaspirated sounds are written like voiced sounds in english, so the sounds /p/, /t/, and /k/ are written as 'b', 'd', and 'g' respectively. for example, the word "gaokao" would be written in ipa as /kau̯.kʰau̯/. in wade-giles spelling, aspirated stops, fricatives, or affricates are written with an apostrophe after the letter instead of using a different letter like in pinyin, so "gaokao" would be written as "kaok'ao" in wade-giles.