Kohaliya 1.4: Abhinavabhāratī (Nāṭyavedavivṛti)

1.4

syād uttamānāṃ dvipadī caturgurusamanvitā | tatrotkṣepanipātābhyāṃ yasmāt pādadvayaṃ bhavet ||

For the highest characters there is the dvipadī with four long syllables, since there the two feet are made by raising and lowering.