These were the musicians who were the heads of the Levite families. They lived in rooms in the temple and were free from other duties because they were on duty day and night.
At the time of Zerubbabel and Nehemiah, all the Israelites were giving gifts for the daily support of the singers and the gatekeepers. They set aside holy gifts for ⌞the daily support of⌟ the Levites, and the Levites set aside holy gifts for support of Aaron’s descendants.