Spanish letter d 

This letter can exhibit two sounds: /d̪/ (Voiced dental stop) and /ð/ (Voiced dental fricative)

The voiced alveolar stop is a type of consonantal sound, used in some spoken languages. The symbol in the International Phonetic Alphabet that represents voiced dental, alveolar, and postalveolar stops is ⟨d⟩ (although the symbol ⟨d̪⟩ can be used to distinguish the dental stop, and ⟨d̠⟩ the postalveolar), and the equivalent X-SAMPA symbol is d.
And it occurs in absolute initial position or after n, l
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Sound 1: Voiced dental stop /d̪/ /ˈd̪ä.ɲo̞/ (damage)    /ˈse̞l.d̪ä/ (cell) /ˈt̪il.d̪e̞/ (accent mark)    /uˈmil.d̪e̞/ (humble) /ˈbäl.d̪e̞/ (bucket)    /e̞m.pɾe̞n̪.d̪e̞ˈðo̞ɾ/ (enterprising) /in̪.d̪ä.ɰäˈsjo̞n/ (investigation)    /ä.pɾe̞n̪.d̪iˈsä.xe̞/ (apprenticeship) /d̪e̞.se̞p.sjo̞ˈnäɾ/ (to disappoint)    /d̪i.miˈt̪iɾ/ (to resign)

The voiced dental fricative is a consonant sound used in some spoken languages. It is familiar to English-speakers, as the th sound in father. Its symbol in the International Phonetic Alphabet is eth, or [ð] and was taken from the Old English and Icelandic letter eth, which could stand for either a voiced or unvoiced interdental non-sibilant fricative. The symbol is also sometimes used to represent the dental approximant, a similar sound, which no language is known to contrast with a dental non-sibilant fricative,[1] but the approximant is more clearly written with the lowering diacritic: ⟨ð̞⟩.
And it occurs whenever the letter d is not in absolute initial position or after n, l

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Sound 2: Voiced dental fricative /ð/ /gäˈnä.ðo̞/ (cattle)    /ko̞n.mo̞.βe̞ˈðo̞ɾ/ (moving) /ä.t̪ɾäˈsä.ðo̞/ (late)    /re̞.ä.nuˈðäɾ/ (to resume) /bo̞.lun̪ˈt̪äð/ (will)    /pɾe̞.ðiˈkäɾ/ (to preach) /e̞s.pe̞ˈɾä.ðo̞/ (anticipated)    /pulˈɰä.ðä/ (inch) /mä.ɾe̞ˈä.ðo̞/ (dizzy)    /päˈɾe̞ð/ (wall)

 The letter f