Here’s another excerpt from the beginning of Eusebius’ Commentary on the Psalms. In it, he discusses the διάψαλμα, or musical interlude, which is used to translate the Hebrew Selah.
Here’s the Greek text and a translation:
Εὐσεβίου Καισαρείας περὶ τοῦ διαψάλματος.
Ἔγραψαν τὸ διάψαλμα οἱ ἑρμηνεύσαντες πέντε ἄρχοντες, οἳ ἐξελέγοντο ὑπὸ Δαυῒδ τοῦ βασιλέως ἐκ τῆς φυλῆς Λευΐ· ὧν τὰ ὀνόματά εἰσι ταῦτα, Ἀσὰφ, οἱ υἱοὶ Κορὲ, Αἰμὰν, Αἰθὰμ, Ἰδιθούμ· τούτοις ἀριθμὸς ᾠδῶν παρηκολούθει, ἑκάστῳ ἑβδομήκοντα δύο. Οὗτοι ἵσταντο ἐνώπιον τοῦ ἁγιάσματος Κυρίου, αἰνοῦντες τὸν πάντων δεσπότην, ὃς μὲν κύμβαλα, ὃς δὲ ψαλτήριον, ὃς δὲ κινύραν, ὃς δὲ κερατίνην, ὃς δὲ κιθάραν ἔχων, ὧν μέσος ἵστατο ὁ Δαυΐδ. Καὶ οὕτως ἤρχοντο τῶν ᾠδῶν κρατοῦντες ἐπὶ χεῖρα τὰ τοιαῦτα ὄργανα· καὶ ἕκαστος Πνεύματι ἁγίῳ κινούμενος ὕμνει 4 τὸν Θεὸν, καὶ πάντες ἐπεφώνουν τῷ ψάλλοντι τὸ Ἀλληλούϊα. Ὁπηνίκα δὲ ἡ τοῦ Πνεύματος τοῦ ἁγίου ἀπέστη χάρις πρὸς βραχὺ, τῶν ὀργάνων λοιπὸν μὴ κινουμένων, τὸ τηνικαῦτα εἰκὸς καὶ τὸ διάψαλμα ἔγραφον.
And here’s my translation:
Eusebius of Caesarea on the Interlude (From PG 23.76)
The diapsalma was written by the five leading proclaimers, who were chosen by King David from the tribe of Levi. Their names were Asaph, the Sons of Korah, Aiman, Aitham and Idithoum. The numbering of the songs follows these closely, each of the seventy two.[*] They stood before the holiness of the Lord, praising the Master of All, one with the cymbals, one with the psalteria, one with the kinuran, one with the keratinen, and one with the harp[**], and David stood in the middle of them. And this is how they began a song, holding in their hands these instruments. One at a time, each would be moved by the Holy Spirit to sing to the Lord, and all would respond to the singing by exclaiming “Hallelujah.” At that time, the grace of the Holy Spirit would abate for a short time, and the rest of the instruments would lay silent, and at a time like this the diapsalma would be written.
* I’m not sure what’s going on here. αριθμος means number, and I take it he’s addressing the numbering or inscriptions of the psalms. 72 refers to the 72 psalms of David.
** All of these are musical instruments. I believe the psalteria is also a type of harp, but I don’t know what exactly the others are.