Q:

How do you extend the sound of a daleth in Shema?

How does one extend the sound of the daleth in the echod of the shema as prescribed in OC 61 (6)?. The letter as we say it does not seem to allow extension. See Dalet (Wikipedia) which defines it as a "a voiced alveolar plosive" and Voiced dental and alveolar stops (Wikipedia) which defines the last term.

A:

Chanoch and Ariel K are correct in their answer, but one can answer at greater length and detail.
The letters beged kefet, בגד כפת are distinguished from other Hebrew letters in taking a dagesh kal, a 'weak' dagesh, at the start of words or after a shva nach. The function of this dagesh kal is to distinguish between the plosive and fricative versions of the letters:

b/v (actually, in Mishnaic Hebrew, bh, the voiced bilabial fricative, rather than the labiodental)
p/f (actually, ph, again unvoiced bilabial rather than unvoiced labiodental)
g/gh
d/dh
t/th

(There is also beged kaperet, where there is a distinction between a resh in front or the back.)
Over the years, different groups have dropped certain of these distinctions, or mapped them to the closest phoneme in the language in their vicinity.
The daled in echad appears at the end of a word, and does not have a dagesh kal. Thus, it should be the fricative -- like the /dh/ in 'either', just as we see the Yemenites have it. 
The gemara speaks of elongating it, which strongly suggests that they made this distinction.
What about us? Well, we could either adopt the /dh/ for the word, for the duration of Shema; or we can ignore the Talmudic instruction, since it is no longer relevant for us.
Similarly, I would not worry about putting a pause between Eisev | BeSadcha and Hakanaf | Petil or Tizkeru | VaAsitem (the last according to the Rif's girsa) in Shema, despite Rava's instruction in Berachot 15b, because Rava was operating with different phonology, as I discuss here:
http://parsha.blogspot.com/2005/03/daf-yomi-brachot-15b-feh_16.html
See also my post on this matter, when we reached it in Daf Yomi, where I also discuss the surrounding gemara.

A:

We pronounce it like the "th" in the word "the".

A:

It is possible to prolong a plosive (stop). You will hear some who are very careful with reading the prayers or the Tora pronounce a dagesh chazak (dagesh forte) as a geminate consonant; this is a longer consonant, and can be done even with a stop. (If you ever hear someone speaking Arabic or Italian (tutto), you can hear geminate stops also. Many other languages have them, too.) Essentially, the voice box keeps trying to operate (in the case of a voiced stop like dalet), but whatever is stopping the airflow (the tongue in the case of dalet) stops it for longer. A book on phonetics will explain it better; I recommend Ladefoged, A Course in Phonetics.
However, I don't know that that's what the halacha is referring to when discussing the dalet of "echad". As always, CYLOR with practical questions.

