Those who were musicians, the heads of Levite families, stayed in the temple chambers and were exempt from other duties because they were on duty day and night.
KJV
And these [are] the singers, chief of the fathers of the Levites, [who remaining] in the chambers [were] free: for they were employed in [that] work day and night.
ASV
And these are the singers, heads of fathers’ houses of the Levites, who dwelt in the chambers and were free from other service; for they were employed in their work day and night.