Talk:Special information tone
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AT&T/Bellcore Standard SIT composition edit
I don't know if it's truly valuable to cite specifically (and only) Bellcore's SIT frequency and duration specifications from 1981 when ITU-T has a much more broadly applicable and current guideline from 1998. These are[1]:
7.2 The special information tone has a tone period theoretically equal in length to the silent period.
Tone period – The tone period consists of three successive tone signals, each lasting for 330 ± 70 milliseconds. Between these tone signals there may be a gap of up to 30 milliseconds.
Silent period – This lasts for 1000 ± 250 milliseconds.
7.3 The frequencies used for the three tone signals are: 950 ± 50 Hz; 1400 ± 50 Hz; 1800 ± 50 Hz, sent in that order.
— Preceding unsigned comment added by 174.90.120.145 (talk) 21:06, 14 November 2017 (UTC)
References