In our Theravada Monastery, (SL tradition partly influenced by Thai forest standards) we understand that "musical chanting" is prohibited by this khandaka rule. By "musical chanting" we draw the line, in practice, by not intentionally mispronouncing the pali or english for the sake of a tune. Now here is the story:
Cullavaga V.33.1 = Vin.II.139:
Now at that time Yameḷu and Tekula were the names of two monkks who were brothers, brahmans by birth, with lovely voices, with lovely enunciation. They approached the Lord; having approached, having greeted the Lord, they sat down at a respectful distance, these monks spoke thus to the Lord: "at present Lord, monks of various names, various clans, various social strata have gone forth from various families; these corrupt the speech of the Awakened One in using his own dialect.1. Now we, Lord, give the speech of the Awakened One in metrical form." 2. the Awakened One, the Lord rebuked them saying: How can you, foolish men, speak thus: 'Now we, Lord, give the speech of the Awakened One in metrical form'? It is not, foolish men for pleasing them who are not (yet) pleased, not for increasing the number of those who are pleased, but, monks, it is displeasing to those who are not pleased as well as to those who are pleased, and it causes wavering in some." And having rebuked them, having given reasoned talk, he addressed the monks, saying, "monks, the speech of the Awakened One should not be given in metrical form. Whoever should (so) give it, there is an offence of wrong-doing. I allow you monks to learn the speech of the Awakened one according to his own dialect.
• 1. sakkāya niruttiyā. V A. 1214 says the current Magadhese manner of speech according to the awakened one.
• 2. Chandaso āropema. V A. 1214 explains "we give (āropema) a way of speech according to the honoured dialect like a Veda." So, Buddhaghosa thought this meant they put in the dialect of the Vedas.