Is the "v" pronounced as a "b"?
I once learned to pronounce the "v" always as if it were a "b". A Cuban teacher I had for a few classes would say that there's really no phonetic distinction. Listening to the audio here, though, I notice that the "v" really sounds like the English "v". Is it a matter of regional accent? Which form is really the correct one?
In nearly all dialects, both letters represent the same phoneme - that is, in nearly all dialects, the only difference between the words "barra" and "vara" is the trill in the r. Both b and v are pronounced using a sound that is not used in English, called a bilabial approximant. This sound is produced like an English v, but while the English v is produced by touching your upper teeth to your lower lip, the bilabial approximant is produced by touching your upper lip to your lower lip - like what you would do to pronounce an English b, except that an English b is a stop, not an approximant.
There may be a few very isolated, regional dialects that preserve a distinction between b and v - that difference existed in older versions of Spanish, and it still exists in Portuguese, though not in Catalan or Galician or Aragonese.
In everyday Spanish, b and v are normally pronounced the same. When preceded by a vowel or another "soft" consonant (and not after a pause), the b/v is "soft" (a fricative) with voiced air passing between the lips (just like the "v" in English but with the lips almost touching each other rather than the upper front teeth and the lower lip of the English "v"). Otherwise, pronounce like a "b" in English. However, probably as French has traditionally been the cool language, Spanish speakers have tried to imitate the difference between "b" and "v" (same in French as in English), so you may hear the English "v" pronunciation for any "b/v" in Spanish. I do hear this in the spoken Spanish in the lessons. So, it is tricky for native English speakers !
I once got dressed down by a Columbian woman, because I pronounced some words as I hear them in Spain: "ciudad" with the lisp at the beginning <thiudad> "jueve" as <xuebe> (x as in Greek). I learned from it, that Southern America and Spain have some different pronounciations and I get the impression thet DuoLingo prefers Southern American.
here, maybe that helps you: http://www.studyspanish.com/pronunciation/letter_bv.htm