You can freely build on How Pulse Code Modulation Digitizes Analog Signals

What this patent covers

This patent describes the process of Pulse Code Modulation (PCM). It works by sampling an analog signal—like a human voice—at regular intervals and assigning a numerical value to the amplitude of the signal at each point. These numbers are then transmitted as a series of pulses, which can be reconstructed back into the original sound wave at the receiving end. This method allows for clearer communication because the digital pulses are easier to filter from noise than a continuous analog signal.

What is now free to use

All 0 claims of US 2266401 are in the public domain. Specifically:

The 0 dependent claims add narrowing limitations and are also free.

What is NOT covered

Patent expiry frees this specific invention. Separately-patented improvements made after expiry may still be protected.

• Does not cover the specific hardware circuitry used in modern microprocessors.

• Does not cover analog-to-digital conversion methods that do not use pulse modulation.

• Does not cover data compression algorithms like MP3 or AAC.

Who is building on this today

Every major telecommunications equipment manufacturer, including Nokia, Ericsson, and Cisco, builds on the principles established here. The core concept of digitizing signals is now a standard taught in every electrical engineering curriculum worldwide.

Products built on expired version of this technology

How to cite this patent in your documentation

International Standard Electric Corp . US Patent 2266401. Signaling system. Granted 1941, expired 1958. Now in the public domain.

Note: This is a convenience citation. Consult a patent attorney for formal freedom-to-operate analysis.

PatentBrief is an educational resource and does not provide legal advice. Patent expiration information is derived from USPTO records and may not reflect continuation patents, divisional filings, or separately-patented improvements. For commercial use or production decisions, obtain a formal freedom-to-operate (FTO) opinion from a registered patent attorney.