audio

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#audio

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What happens when you press 5 on a phone call Oct 17, 2026 A key press is two sine waves. On a modern VoIP call it is usually not sound at all, but a small packet that says which key and for how long. A walk from the 1960 Bell Labs design to RFC 4733, with the codec test that drops digits. 9 min read #systems#telephony#voip