AES vs PCM

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HeWhoShallNotBeNamed
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Joined: Thu Feb 02, 2012 3:27 pm

AES vs PCM

Post by HeWhoShallNotBeNamed » Sun Aug 18, 2013 6:14 am

I have always considered AES
- synonymous with a physical cabling format. Eg a 15 pin serial cable / port.
- a method of supplying PCM audio, separate to video IE:
- AES is not the carrier / container for PCM delivered via SDI signal with video

Is the above correct? If not can you correct my understanding please...

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PID_Stop
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Re: AES vs PCM

Post by PID_Stop » Mon Aug 19, 2013 2:39 pm

HeWhoShallNotBeNamed wrote:I have always considered AES
- synonymous with a physical cabling format. Eg a 15 pin serial cable / port.
- a method of supplying PCM audio, separate to video IE:
- AES is not the carrier / container for PCM delivered via SDI signal with video

Is the above correct? If not can you correct my understanding please...
AES3, also known as AES/EBU audio, combines physical specifications for the cabling with the protocol under which the data is transmitted. There are a handful of variants (for example, Type I is 110-ohm balanced; AES-3id is the 75 ohm unbalanced coaxial link with BNC connectors.)

Generally speaking, an AES feed consists of two pulse code modulation (PCM) channels -- that is, a stereo pair. But there are applications that use the AES transport for other coding schemes: for example, Dolby E and Dolby AC3 can look like AES signals to the point where sometimes they can be embedded in digital video as if they were PCM feeds. Most video equipment that handles embedded audio tends to refer to digital audio as AES to distinguish inputs and outputs from analog, and oftentimes the stereo pairs are referred to as AES 1 (channels 1 and 2), AES 2 (channels 3 and 4), and so forth. This might not be technically proper usage, but I do see that in real-world equipment; if I remember correctly, the actual standard for embedded audio is SMPTE 291M... but that refers back to AES.

Clear as mud, right?

-- Jeff

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