Read 1 Chronicles 9:33 Using Other Translations
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.
Now these, the singers, the heads of fathers' houses of the Levites, were in the chambers of the temple free from other service, for they were on duty day and night.
The musicians, all prominent Levites, lived at the Temple. They were exempt from other responsibilities since they were on duty at all hours.