Module tones 

Telephony tone synthesis.

Call-progress tones are not recordings — they are specifications (ITU-T E.180 and the national supplements): a few sine frequencies in a fixed on/off cadence. Generating them beats shipping WAV files on every count: nothing to license, any sample rate we like instead of 8 kHz mu-law, an exact cadence, and a seamless loop.

A tone is written the way Asterisk’s indications.conf writes it, so any of its 50 country zones can be pasted in verbatim:

425/1000,0/4000        Germany, ringback: 425 Hz for 1 s, then 4 s of silence
440+480/2000,0/4000    North America, ringback: two mixed frequencies

Elements are separated by commas; each is freq[+freq…]/milliseconds, and a frequency of 0 is silence. Asterisk’s * (modulation) and ! (play once) are not supported — say so in the error rather than mis-playing them.

Structs

Chime

A short motif of struck notes, plus the silence that follows it — so a looping alert carries its own cadence and needs no gap bolted on.

ParseError

Why a tone spec could not be read. The message completes the sentence “the tone …”, so it reads as one line in a log.

Partial

A partial of a struck note: its frequency as a multiple of the fundamental, and its amplitude relative to it.

Segment

One stretch of a tone: which frequencies sound, and for how long. An empty freqs is silence — that is how a cadence’s gap is written.

Timbre

How a struck note is coloured and how long it rings.

Tone

A complete tone: the segments of exactly one cadence period.

Constants

DE_BUSY

Germany, busy (Besetztton) — the called party is on the phone. Asterisk zone [de], busy.

DE_CONGESTION

Germany, congestion (Gassenbesetztton) — the network could not put the call through. Same frequency as busy at twice the rate, which is exactly the distinction between a SIP 486 and any other failure. Asterisk zone [de], congestion.

DE_RINGBACK

Germany, ringback (Freiton). Shared with most of Europe and, per ITU-T, much of the world. Asterisk zone [de], ring.

MESSAGE

New voicemail: two descending notes, played once. Deliberately smaller than the ring — it reports something, it does not ask for you.

RING

Incoming call: an ascending G–C–E triad, repeating every 2.5 s. Modern ringtones are a short motif in a cadence, not a continuous tone.

SOFT

Nearly a pure sine, with a touch of the octave — the quietest of the timbres we tried, and the one that stays bearable on the tenth repetition. Adding another is six lines: partials as multiples of the fundamental, plus a decay. A marimba is 1/4/10 and 600 ms, struck glass 1/2/2.4/3/4.5 and 1100 ms.

Functions

render

Render periods repetitions of tone as mono S16 samples at srate.

render_chime

Render one period of chime as mono S16 samples at srate.