The voiced retroflex trill is not a single consonant quality but a sliding cluster sound within the time of a single segment. It has been reported in Toda and confirmed with laboratory measurements. Peter Ladefoged transcribes it with the IPA symbol that is normally associated with the retroflex flap, ⟨ɽ⟩. Although the tongue starts out in a subapical retroflex position, trilling involves the tip of the tongue and causes it to move forward to the alveolar ridge. Thus, the retroflex trill gives a preceding vowel retroflex coloration, like other retroflex consonants, but the vibration itself is not much different from an alveolar trill. Thus, the narrower transcription ⟨ɽr⟩ is also appropriate.
Wintu and Lardil are other languages with a reported (apico-)retroflex trill where the tongue apex "approaches" the hard palate, but it is not subapical, unlike in Toda. The trill has a retroflex flap allophone that occurs between vowels.
Variations of the retroflex trill in IPA symbols
Several languages have been reported to have trilled retroflex affricates such as [ɳɖ͡ɽ̝] and [ʈ͡ɽ̝̊], including Mapudungun, Malagasy and Fijian. However, the exact articulation is seldom clear from descriptions.
In Fijian, for example, further investigation has revealed that the sound (written ⟨dr⟩) is seldom trilled but is usually realized as a postalveolar stop [n̠d̠] instead. In Mapudungun, the sound (written tr) is strongly retroflex, causing /l/ and /r/ following the subsequent vowel to become retroflex as well. The southern dialect varies between /ʈɽ/ and /ʈʂ/, but it is not clear whether the letter ⟨ɽ⟩ represents a trill or a non-sibilant fricative.
