ट (ṭ) series

For the next series of letters, the ट (ṭ) series, the tip of the tongue is put on the top of the mouth.  These characters are referred to as retroflex.  They sound like the English "t" but the tongue is up higher in the mouth (in English the tip of the tongue is usually put on the ridge above the top row of teeth).  When transcribing English words into Hindi, this sound is used.  When romanized in scholary works, it is often represented with a dot underneath (ṭ).

The first character ट (ṭ) in this series contains no aspiration (puff of air exhaled at the end of the sound):

Yo

 

The next character ठ (ṭh) does have aspiration:

 

Yo

 

The next character is ड (ḍ), a "d" sound with the tip of the tongue at the top of the mouth.  Like "t" the "d" is usually pronounced in English with the tip of the tongue on the ridge above the top row of teeth.  That sound does not exist in Hindi, so this character is used to transcribe the English D sound.  It has no aspiration:

 

Yo

 

The next character is ढ (ḍh).  It does have aspiration:

 

Yo

 

The last character is a nasal, pronounced with the tip of the tongue at the top of the mouth.  It will usually occur in Hindi before the ट, ठ, ड, and ढ characters:

 

Yo