A Multi-Channel Audio Primer – Are You Listening?

January 20, 2010 at 2:09 am | Posted in Uncategorized | Leave a comment

This is gonna be an acronym-fest. I’m sorry.  I’ll break this in a copule of paragraphs, you can follow the link if you want to learn something about what you are hearing or what your buttons on the A/V receiver remote actually do.

Multi-channel audio is a product of the movies. Although there are a couple of examples where it applies to music, its main purpose is to enhance movies. If you are concerned with perfect imaging of orchestral music or being able to place Phil Collins’ snare drum while listening to headphones…this is not the article you are looking for. Move along.

So, are you ready for a quick primer on home and theater sound system differences. Dolby vs THX? SDDS vs DTS? Then follow me…

Your Home Stereo. 2 Channels. Left and right. You have two ears, this has two speakers. It’s old school. Applies more to music than movies these days…let’s move on.

Mono: One channel. Way old school. One speaker. In a theater it would be behind the screen. Back in the day; when movies were mostly dialogue, with very few explosions or  side-to-side car chases or slow-motion/multi-camera-shot gunfights…this was the de facto standard. Things were recorded with one microphone (in mono) and played back that way. If you have some really old movie (or is a home movie) and it wasn’t remastered for whatever reason…this may be your answer – the dialog will be centered on screen (provided you have a center channel speaker) and it should be clear as a bell (provided the original recording didn’t suck).

Movie Stereo: Yeah, that’s a term I just made up…but this gets complicated. Tecnically stereo is 2 or more channels of sound, but most people think of their old “hi-fi” or their Ipod when they think stereo. That’s not the case with “movie stereo”. Movie stereo can have 2, 3, 4…however-many channels. Usually its 2, in the traditional sense of the word like you are thinking. In the movies it can be 3 (Left-Right-Center…see how they took your home stereo and added that mono channel so you could hear dialog in the middle but hear the man walk in the door over to the left?) Maybe its 4. That adds a surround channel. Usually in the back, so you can hear it rain behind you when the camera pans from the storm outside the window to the person that snuck up behind you. Dolby has had its foot in this door for a long time. Dolby Stereo uses 4 channels, as I just described – in an analog format. No digital compression losses. Think 4 track tape if you are that old.

Dolby SR: The de facto recording standard on 35mm films. Stands for Spectral Recording. It is a 4 cahnnel noise reduction system used by the pros. Think of the Dolby C switch on your old tape deck – only on steroids. Does not only the noise reduction, but adds the other channels to the optical soundtrack area of 35mm film.

Dolby C: The switch on your old “hi-fi” that reduced that irritating hiss on cassette tapes. Other versions exist such as A and B or S…not really our concern here.

Dolby Digital: a 6 channel surround sound process that has Left/Center/Right/Left Surround/Right Surround/Subwoofer so, its usually called 5.1 as the 6th channel is just used to make things go boom (known as the Low Frequency Effects channel or LFE) This was known as AC3 back in the days of laserdisc. Its digital, and subject to losses via compression (lossy).

Dolby Digital EX: Same as above, only it adds a rear center channel to the mix. That’s 6.1 sound.  Sometimes it splits this into two rears 7.1 . So you know when the jet is circling back to shoot at you again.  Digital. Lossy.

Dolby True HD: 7.1 State-of the art stuff. Digital, lossless (like a studio master tape) Takes a lot of storage space, so you find it on things like BluRays.

Dolby Pro Logic: 4 channels. L/R/C/Surround. The home version to use when watching a Dolby Surround film, I suppose. Good for TV shows that aren’t broadcast in 5.1. There are new versions of this that will do 5.1, 6.1…you get the idea. The higher the number/letter after this designates how many channels it will decode/upconvert from a 2 channel broadcast. The latest versions IIZ, I think, will go up to 9.1 channels which include height information so you can listen to a rocket start at the bottom of your screen and go upwards, then fall back down. Probably great if you are blind and rich and listen to a lot of movies with rockets.

THX: This is a playback standard developed by Lucasfilm. It measures stuff like component distortion, noise leakage from a room, does some re-equalization based on room specs., etc. Suffice it to say – if you have a lot of money and buy all THX approved gear, you need to hire a THX certified guy come out and design and build a room to put it all in. Then he will tweak it all to sound just like it sounded at the sound studio when they mastered the film. The ultimate. Not cheap. Pressing the THX button on your remote does a lot of stuff, most of it doesn’t count unless your viewing area is optimized and your friends and girlfriend/wife like to hear stuff at reference volume. That means your THX cetified everything is turned to reference and when the Death Star explodes, it sounds like a small planetoid just exploded. 2 subwoofers help.

DTS: Steven Spielberg’s answer to audio when Jurassic Park was released. A digital soundtrack developed by Sony called SDDS (Sony Dynamic Digital Sound). Kind of their alternative to Dolby SR. Perfect for when you need your bottle of beer to shake in unison with the puddle in Jurassic Park. All the channels you want. Reference volume applies here. If others in the house don’t come running into your non-THX approved media room saying “it sounded like a helicopter was landing in here” then you weren’t watching the part of JP where the helicopter lands. On laserdisc or BluRay so you have uncompressed audio. Screw that compressed DVD stuff.

Its late. My brain is blank on some other acronyms that may apply. If you have questions – ask em. I’ll answer ’em.


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