It was a habit born of long training, turning sibilant consonants that carried for long distances into fricative soft sounds.

For example, the folded-cloth glyph seems to have been originally an voiceless alveolar fricative and the door-bolt glyph a voiceless dental fricative sound, but these both came to be pronounced , as the sound was lost.

The reconstruction of Proto-Semitic has nine fricative sounds that are mostly reflected as sibilants in later languages, although it is a matter of dispute whether all started as sibilants already in PS:

Whether in orthography or ortheopy, the major disparity is at the level of the affricate and fricative sounds.

Among consonant letters, all letters that denoted voiced plosive consonants (/b, d, g/) and aspirated plosives (/pʰ, tʰ, kʰ/) in Ancient Greek stand for corresponding fricative sounds in Modern Greek.

In Welsh, ll stands for a voiceless lateral fricative sound.

The same evidence is also consistent with the assumption that they were fricative sounds (as opposed to approximants or stops), an assumption which is strongly supported by the behaviour of laryngeals in consonant clusters.

An example of a characteristic would be the fricative consonant sound called ṣafīr, which is an attribute of air escaping from a tube.

The two sounds most commonly used to establish a patient's VDO are sibilant and fricative sounds.

Ahh . . . And he recalled the heavy fricative greeting sound.