Spanish /b/, /d/, and /g/ are realized as plosives or stops after a pause and after nasals (/d/ is also realized as a stop after the letter "l"). In all other cases, these sounds are pronounced as fricatives: [β], [ð], and [ɣ] respectively. [β] and [ɣ] do not have equivalents in English, but [ð] is the sound in the English word "the." This is why for a word like "deuda" you might hear something like "deutha."
Think of if this way: the letters "b", "d", and "g" in Spanish are always pronounced as fricatives unless they come at the beginning of an utterance or after a nasal:
- After a pause basically means if it's the first sound in a sentence or utterance. For example, the "g" in "guerra" will sound different if you just say this word in isolation, versus if you say it preceded by something, e.g. "la guerra." In isolation, it is pronounced as a plosive: [gera] because it is after a pause. When it is preceded by something, it reverts to a fricative: [la ɣera].
- The two relevant nasals are "m" and "n". After these two letters, /b/ /d/ and /g/ are also realized as stops. for example: banda [banda], noviembre [noβiembɾe]*.
- /d/ additionally also becomes a stop after the letter "l". For example: el desarrollo [el desaroʝo], caldo [kaldo].
In all other cases, these letters are pronounced as fricatives.
- barbaridad [barβaɾiðað]
- Cuba [kuβa]
- cambiaba [kambjaβa]
- Estados Unidos [estaðos uniðos]
- Gabriel [gaβɾjel]
- el carro de Gabriel [el karo ðe ɣaβɾjel]
*Interestingly, the letters "b" and "v" in Spanish actually represent the same phoneme. I.e., if the word noviembre were spelled nobiembre, it would be pronounced the same.
