At the March 18 meeting...

Digital Audio

Explanations and Amplification

By Bob Lamm

Jim Hilson from Dolby Labs was the speaker at the March 18 meeting. He explained the intricacies of all the different ways digital audio can be coded. Dolby has been doing lots of work on sensurround-type audio setups such as are found in theaters. Although these started out as analog systems with the various channels multiplexed on existing movie film in various ways, they’ve evolved into digital systems that people can use at home.

The most common configuration is called 5.1: there are five real channels: left, right, center, left rear and right rear. The '.1' is for the effect speaker that sits in the middle of the room and typically provides the bass 'magic fingers' sound. Setting these systems up satisfactorily is a bit of an art, but one of the basic rules is to try and keep the speakers matched so that the sound doesn't change as it's panned across them. It's also good practice to put dialogue in the center track and leave the peripheral speakers for effects so that people who aren't in the center of the room don't get inconsistent audio. It also turns out that the spatial separation of effects and dialogue coming out of different speakers makes it easier for the audience to distinguish the two and one can turn those effects up louder without swamping the speech. But it also means that mixes created for 5.1 can't be mixed down to stereo without rebalancing the audio or the effects will overpower the dialogue.

Jim also played a couple of DVD examples. One was a music video by Bryan Adams, it was pretty good although the intended audience was probably a little younger than was present that night. Another CD was of a concert by a band I won’t name that was pretty badly mixed: things that should have been loud (like trumpets) were way too soft, the directionality of the mix was inconsistent with where things actually were on screen.

All in all, it was an excellent presentation. And it was preceded by a presentation by Joe Wellman from N-Vision on AES/EBU audio. Unfortunately, the whole thing was so much over my head that I couldn't do justice to the material. But Mark Parsons from Parsons Audio will be doing an overview at the May 23 meeting...

Bob Lamm is Manager at CYNC Corp.,a video dealership that He can be reached at 617-277-4317,

Posted: 20 April, 1998
Robert Lamm, SMPTE/New England Newsletter/Web Page Editor