A voiceless alveolar trill differs from the voiced alveolar trill /r/ only by the vibrations of the vocal cord. It occurs in a few languages, usually alongside the voiced version, as a similar phoneme or an allophone.
Proto-Indo-European *sr developed into a sound spelled ⟨ῥ⟩, with the letter for /r/ and the diacritic for /h/, in Ancient Greek. It was probably a voiceless alveolar trill and became the regular word-initial allophone of /r/ in standard Attic Greek that has disappeared in Modern Greek.
PIE *srew- > Ancient Greek ῥέω "flow", possibly [r̥é.oː]
Features of the voiceless alveolar trill:
Its manner of articulation is trill, which means it is produced by directing air over the articulator so that it vibrates.
Its place of articulation is dental, alveolar or post-alveolar, which means it is articulated behind upper front teeth, at the alveolar ridge or behind the alveolar ridge. It is most often apical, which means that it is pronounced with the tip of the tongue.
Its phonation is voiceless, which means it is produced without vibrations of the vocal cords. In some languages the vocal cords are actively separated, so it is always voiceless; in others the cords are lax, so that it may take on the voicing of adjacent sounds.
It is an oral consonant, which means air is allowed to escape through the mouth only.
It is a central consonant, which means it is produced by directing the airstream along the center of the tongue, rather than to the sides.
The airstream mechanism is pulmonic, which means it is articulated by pushing air solely with the lungs and diaphragm, as in most sounds.
Alveolar
The voiceless alveolar raised non-sonorant trill is not known to occur as a phoneme in any language. However, it occurs allophonically in Czech.
Features of the voiceless alveolar raised non-sonorant trill:
Its manner of articulation is fricative trill, which means it is a non-sibilant fricative and a trill pronounced simultaneously.
Its place of articulation is laminal alveolar, which means it is articulated with the blade of the tongue at the alveolar ridge,
Its phonation is voiceless, which means it is produced without vibrations of the vocal cords. In some languages the vocal cords are actively separated, so it is always voiceless; in others the cords are lax, so that it may take on the voicing of adjacent sounds.
It is an oral consonant, which means air is allowed to escape through the mouth only.
It is a central consonant, which means it is produced by directing the airstream along the center of the tongue, rather than to the sides.
The airstream mechanism is pulmonic, which means it is articulated by pushing air solely with the lungs and diaphragm, as in most sounds.
