> For the complete documentation index, see [llms.txt](https://prosbcdocs.telcobridges.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://prosbcdocs.telcobridges.com/telecom-references/protocols/pcm.md). # PCM Pulse Code Modulation is a digital encoding of an analog audio signal. PCM is the native audio encoding format for voice and other audio on wireline and mobile networks based on the [TDM](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/transmission/tdm/README.md) standard. ### TelcoBridges and PCM Applications on the [Tmedia](https://telcobridges.com/media-gateways/products/tmedia-gateways/) or [Tdev](https://telcobridges.com/products/development-platforms-tdev/) platforms that require audio to be recorded or played back use [TB StreamServer](https://github.com/telcobridges-main/tmedia-wiki/tree/main/tmedia/operations/tb-streamserver/README.md) which provides native support for PCM encoded audio files. An example of the use of TB StreamServer and PCM files is the following: two participants are on a conference call hosted by a Tmedia or Tdev device; the call is being recorded for posterity. The first person accesses the call via a traditional TDM-based landline telephone; the second accesses the call via a [VoIP](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/sip-voip/voip/README.md)-enabled device. Since the voice media on the TDM landline is already encoded in PCM by the caller's handset, the audio is captured by the Tmedia or Tdev device and written to disk with no audio format conversion required. However, for the person using the VoIP device, there are a few extra steps involved. In this case, the Tmedia or Tdev device must first convert the call media from whichever [voice encoding method](https://github.com/telcobridges-main/tmedia-wiki/tree/main/reference/voice-media/voice-codecs/README.md) was being used into PCM format. In short, the RTP packets are sent to the VoIP chip on the Tmedia or Tdev device from where they are converted to PCM and then written to disk in PCM format for storage. When the contents of the conference call are played back for a called using VoIP, the process is reversed. The audio is taken from PCM format and converted into a codec that can be used over a packet network like the Internet. Should another person using a TDM-enabled landline also choose to playback the conference call, no conversion is required. The audio remains in PCM format throughout the process. ### References * [Wikipedia article](http://en.wikipedia.org/wiki/Pulse-code_modulation) --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://prosbcdocs.telcobridges.com/telecom-references/protocols/pcm.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.