zh ch sh vs. z c s

[Xiying]

My parents are Taiwanese and I can't distinguish between the retroflex sounds zh ch sh and the non-retroflex z c s. Are there any audio files somewhere that I can listen to so I can get this right?

[kudra]

go to www.adsotrans.com

go to the advanced page

type in 之 for example

under style choose sounds

click adsotate

click on the character to download .wav file

or

go to http://www.mandarintools.com/chardict.html

type in zhi into the pinyin slot

click search by pinyin

click on the pinyin zhi1 and you will get a link to an audio file