Breathy voice

Murmur (also called breathy voice, whispery voice, soughing and susurration) is a phonation in which the vocal folds vibrate, as they do in normal (modal) voicing, but are adjusted to let more air escape which produces a sighing-like sound. A simple murmured phonation, (not actually a fricative consonant, as a literal reading of the IPA chart would suggest), can sometimes be heard as an allophone of English  between vowels, such as in the word behind, for some speakers.

In the context of the Indo-Aryan languages like Sanskrit and Hindi and comparative Indo-European studies, murmured consonants are often called voiced aspirated, as in the Hindi and Sanskrit stops normally denoted bh, dh, ḍh, jh, and gh and the reconstructed Proto-Indo-European phoneme gʷʰ. From an articulatory perspective, that terminology is incorrect, as murmur is a different type of phonation from aspiration. However, murmured and aspirated stops are acoustically similar in that in both cases there is a delay in the onset of full voicing. In the history of several languages, like Greek and some varieties of Chinese, murmured stops have developed into aspirated stops.

There is some confusion as to the nature of murmured phonation. The IPA and authors such as Peter Ladefoged equate phonemically contrastive murmur with breathy voice in which the vocal folds are held with lower tension (and further apart) than in modal voice, with a concomitant increase in airflow and slower vibration of the glottis. In that model, murmur is a point in a continuum of glottal aperture between modal voice and breath phonation (voicelessness).

Others, such as Laver, Catford, Trask and the authors of the Voice Quality Symbols (VoQS), equate murmur with whispery voice in which the vocal folds or, at least, the anterior part of the vocal folds vibrates, as in modal voice, but the arytenoid cartilages are held apart to allow a large turbulent airflow between them. In that model, murmur is a compound phonation of approximately modal voice plus whisper.

It is possible that the realization of murmur varies among individuals or languages. The IPA uses the term "breathy voice", but VoQS uses the term "whispery voice". Both accept the term "murmur", popularised by Ladefoged.