Home Computer Audio Asylum

Music servers and other computer based digital audio technologies.

HDMI has the highest jitter of any interface

HDMI is an abortion of an interface that was crammed down our throats by Sony and Hollywood. Silicon Image was the party that made it all possible.

The idea by Sony was to have the audio and the video both on the same cable, to avoid confusing the schmucks who buy their Sony TV sets at Best Buy and can't figure out how to connect it. Hollywood demanded "content protection", and it was decided that HDCP as developed by Intel would suffice. Silicon Image was determined to develop the silicon chips so that they could cash in on the cash cow.

Of the many problems associated with HDMI, the audio quality is totally handicapped for lack of -- a pin! They designed the connector before they finished designing the system. They didn't have enough pins to also have a master audio clock.

So with HDMI, the audio clock is derived from the video clock. For high-def TV, the video clock runs at either 74.25 MHz or 74.25 * (1000/1001) [thank you NTSC!!!]. The audio clock runs at multiples of 48 kHz. Of course, these are not related. So the receiver has a PLL to regenerate an audio clock based on instructions from the transmitter (source) telling it what to do.

The result is the worst jitter of any system yet invented. It truly sucks.

Much later, they added a thing called Audio Rate Control in HDMI 1.3a. This puts a buffer and the master audio clock in the receiver. Then commands are sent upstream on the CEC line telling the player to speed up and slow down as necessary to keep the buffer full.

The only people to use this are Sony (HATS) and Pioneer (PQLS), but both use proprietary implementations that prevent use with other equipment.

And the fee for using this pile of steaming dog dung? $30,000 per year in licensing fees. It's a beautiful world, no?

This post is made possible by the generous support of people like you and our sponsors:
  Parts Connexion  

Follow Ups Full Thread
Follow Ups


Post a Message!

Forgot Password?
Moniker (Username):
Password (Optional):
  Remember my Moniker & Password  (What's this?)    Eat Me
E-Mail (Optional):
Message:   (Posts are subject to Content Rules)
Optional Link URL:
Optional Link Title:
Optional Image URL:
Upload Image:
E-mail Replies:  Automagically notify you when someone responds.