Each morning, we recite at the end of the "Pesukei De'zimra" service the song of "Az Yashir," which is taken from the Book of Shemot (chapter 15).
Some controversy exists among the Halachic authorities concerning the proper pronunciation of one of the phrases in this poem: "Salelu Ka'oferet Be'mayim Adirim," which describes the Egyptians drowning "like lead" in the waters of the sea. The first three words – "Salelu Ka'oferet Be'mayim" – means "They drowned like lead in water." The final word of this clause, "Adirim," means "mighty," but it is unclear which noun this term modifies. According to most authorities, it describes the Egyptian soldiers, and thus this clause reads, "They drowned like lead in water – the mighty ones." This reading would require making a pause in between the words "Be'mayim" and "Adirim." The Te'amim (cantillation notes) of this verse appear to support this reading, as the "Tarha" note, which indicates a pause, is placed underneath the word "Be'mayim."
Accordingly, the Mishna Berura (commentary to the Shulhan Aruch by Rabbi Yisrael Kagan, Lithuania, 1839-1933) rules (51:27) that when reading this phrase one must pause in between the words "Be'mayim" and "Adirim." This is also the position of the Ben Ish Hai (Rabbi Yosef Haim of Baghdad, 1833-1909), in Parashat Vayigash (14).
However, Hacham Ovadia Yosef, in his work Yabia Omer (vol. 9, p. 32), cites a Midrashic passage indicating that the word "Adirim" can also be used in reference to raging ocean waters. If so, then the words "Be'mayim Adirim" may be understood to mean "in the mighty waters," in which case no pause would be necessary in between the two words. Hence, Hacham Ovadia rules that although a person should certainly follow the majority position and make a pause before the word "Adirim," those who do not make a pause have a source on which to rely.
Towards the beginning of "Az Yashir," we find the expression "Ki Ga'o Ga'a" – "for He is very exalted." According to the laws of grammar, when the letter "Gimal" appears at the beginning of the word, it has a Dagesh (dot) and is thus pronounced like the hard consonant "g," unless the previous word ends with an "Alef," "Hei," "Vav" or "Yod." The words "Ga'o Ga'a" both begin with a "Gimal" and are immediately preceded by a "Yod" ("Ki Ga'o") or a "Hei" ("Ga'o Ga'a"), and it would thus appear that both should be pronounced without a Dagesh, similar to the letter "r." Nevertheless, the common practice is to pronounce the "Gimal" in "Ga'o" without a Dagesh, but to pronounce the "Gimal" of "Ga'a" with a Dagesh.
Another exception to this rule occurs later in "Az Yashir," in the phrase "Am Zu Ga'alta." The "Gimal" at the beginning of "Ga'alta" appears immediately following the letter "Vav," and therefore should, strictly speaking, be pronounced without a Dagesh, but nevertheless the widespread custom is to pronounce it with a Dagesh.
Summary: When reciting in "Az Yashir" the phrase "Salelu Ka'oferet Be'mayim Adirim," it is preferable to make a pause before the word "Adirim." When reciting the phrase "Ki Ga'o Ga'a," one should pronounce the "Gimal" of "Ga'o" without a Dagesh (similar to an "r" sound) and the "Gimal" of "Ga'o" with a Dagesh (like the "g" sound as in "good"). In the phrase "Am Zu Ga'alta," the "Gimal" of "Ga'alta" should be pronounced with a Dagesh (like the hard "g" sound).