In my limited experience in religious congregations, I’ve never attended a synagogue. In my experiences (all Christian), everyone sings during the services, choir and congregation. Does the cantor sing alone, or lead the congregation.
Related question: Do mosques have similar “services” where the imam selects some subject and sermonizes? Is there singing involved?
In a mosque, the imam does sermonize so to speak but not during every prayer (ie. not 5 times a day) but it also depends on the mosque. During noon Friday prayers or a holiday such as Eid Al-Fitr, the imam does deliver a long speech, but I personally don’t know the exact contents as its usually in Arabic, the most-spoken language of the community the mosque is situated in, or the native-language of the imam, none of which I usually understand. From the little bits I’ve picked up, the topics can be political in nature and mention the plight of the Muslim people, the status of Islam, etc. all in relation to the Prophet (PBUH) and the Koran.
In terms of singing, its not formal such as a choir, but the imam often does speak the first few verses of prayer aloud, and at times is echoed by the congregation. This can often be quite harmonious and breathtaking to listen to when literally 1000s of men usually chant in unison.
Cantors can serve several functions (and are used in some Christian services, as well).
Singing or chanting specific prayers/psalms/songs that call for a solo voice.
Leading the congregation in an antiphonal psalm or song. In this case, the cantor sings a line and the congregation responds to that line, either with a rejoinder or with a refrain.
Leading the congregation by getting out front with a strong voice to carry them along.
From Nation-Master:
The hazzan, Hebrew for “Cantor”, is a Jewish clergyperson. A hazzan is a musician trained in the vocal arts, to help lead the congregation in songful prayer.
My father told me about a female soloist at our Protestant church, who had a great voice, and who got a job as a cantor at a synagogue. They didn’t care that she was not Jewish. This was about 30 years ago.
Traditional Jewish services, musically speaking, end up being a mix of chanted/recited texts (some done out loud, some silently) and song-like portions. Cantors end up introducing the song-like portions and leading the congregation in them, as Tomndebb mentioned, as well as “pacing” (for lack of a better word) the silent portions of the service by chanting the last few verses of each psalm or text aloud as he or she reaches them.
Our synagogue is mostly lay-led and the “cantors” are drawn from attendees who can lead the congregation with the traditional modes and melodies (nusach in Hebrew) for different parts of the service.
The best way to get a sense of what a cantor does, IMO, is to go to a synagogue on a Saturday morning and attend a service – just sit discreetly at the back of the room and no-one should bother you.