3 ms·
The "unknown machine" sounds like dtmf tones + pulse tones. It's anyone's guess what the actual meaning of the numbers are, but the tone+pulse encoding suggests
by ashleyn 5y ago
The "unknown machine" sounds like dtmf tones + pulse tones. It's anyone's guess what the actual meaning of the numbers are, but the tone+pulse encoding suggests a super legacy, perhaps proprietary automated system that you'd call up to get the status of something - maybe factory machinery or a power plant, but really it's anyone's guess. Pulse dialing was still somewhat common until the mid 80s so this system is potentially upwards of 40 years old.
- roliver 5y agoCould it be an auto-answer from a Telex machine? https://youtu.be/lCZmVXGyVQQ?t=15 https://youtu.be/lCZmVXGyVQQ?t=15 I have no idea what they sound like on a telephone line though.
- GrumpyNl 5y agoSounds like broken audio file on the other end.
- teeray 5y agoIt reminded me of alarm central station protocols. The earliest (e.g. 3/1 and 4/2) use pulse, and the later ones (Contact ID, SIA) use DTMF [0]. These systems are still installed and relied upon by alarms today. It does seem the industry is finally coming around to LTE, since a copper pair is basically a fiction we present to alarms at this point. [0] https://www.emergency24.com/cp/formats.aspx https://www.emergency24.com/cp/formats.aspx has a cursory overview of many protocols