quote:

Originally posted by Lefty Sig:
Dolby Pro Logic is also analog, and uses L-R for the rears. The analog decoder chip steers all content that is equal in volume in both the Left and Right front channels to the center. Essentially everything that is mono goes to center.

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Pro Logic II does the same thing as Pro Logic but in the digital domain - mono to center, L-R to rears. It's not creating or synthesizing anything, just applying the codec.

Did you actually read Dolby Labs' own statements wrt to Dolby Pro Logic II?

Or try this:

quote:

Dolby Pro Logic II

DPL II processes any high-quality stereo signal source into five separate full frequency channels (right front, center, left front, right rear and left rear), while also decoding 5 channels from stereo signals encoded in traditional four-channel Dolby Surround. DPL II implements greatly enhanced steering compared to DPL, and as a result, offers an exceptionally stable sound field that simulates 5 channel surround sound.

[Note emphasis]
Source: Dolby Pro Logic: Dolby Pro Logic II

^ I understand how it works regardless of Dolby's ad copy. The Wikipedia link says Pro Logic II uses servo (negative feedback) loops to separate the 2 channel content into 5 channels, and since it's all done digitally the steering of mono content to the center has greater separation than the old analog system. It just moves content around, it doesn't create new content. The L-R signal is given some phase delay to differentiate the two rear channels. Did you ever wire one of your Left or Right main speakers backwards so they are out of phase? It makes the stereo image "bigger" but more diffuse. Apple (and others) use selective phase delays (the amount of phase delay depends on frequency) to make headphones and stereo speakers have a "surround" effect. My bedroom system is two Apple Homepods - one on each nightstand - as a stereo pair, wirelessly linked to an Apple TV. The "surround" setting for mixing down 5.1 does sound better than straight stereo mixdown.

Now, the silly modes "Jazz, Hall, Stadium" on many consumer mass market products DO add extra content in the form of digital reverb. This is a low grade version of the processing used in recording studios to "synthesize" a soundstage from close-mic'ed sources in an anechoic recording studio. I don't use these modes.

My rear channels are dipolar - with drivers on the front and rear but nothing pointing at the listener. Treble and mid are out of phase, while bass is in-phase to prevent it from cancelling out. The resulting soundstage is diffuse and very natural sounding, and avoids the impression that a surround effect is coming from "right there" over your shoulder. True 5.1 music is usually mixed for direct speakers but movies generally sound better with dipolars, so it's a compromise. Dolby Atmos is really intended for direct speakers and I have a pair that matches the rest of the system that I can use for the rears if I decide to. Really I'd like to be able to set them both up and be able to select between them. Then again, I might hang the direct pair on the wall for "height" channels since those are discrete in Atmos as well.

Adding any EQ on playback changes the tone and introduces phase shifts that can affect imaging. How many people take any multi-band EQ and boost bass/treble and cut mids? Judging from home audio sections at stores, and tone settings on rental car audio systems, a ton of people do this. We call it the "rock and roll smile" because of the v-shaped curve on a 5 or more band EQ and I've heard it done so badly at clubs and bars that all you hear is bass drum and cymbals and the midrange gets lost.

Sitting anywhere but the sweet spot between two stereo speakers (equilateral triangle with the listener) also causes phase delays that affect imaging. I remember some "audiophiles" insisting that speaker wires had to be the exact same length to avoid phase delays between the Left and Right. When I still remembered how to do the math, I calculated the phase delay between unequal speaker wires differing in length by 10 ft different was equivalent to moving your head a fraction of an inch from the "sweet spot".

But all room correction systems use multiple narrow band EQ's to cut and boost problematic frequencies, and time/phase delays to adjust for speaker distances and placement. And in my experience Audyssey really does work very well to improve the in-room sound. In my system it evens out the midrange, tightens up the bass, and keeps the Seismic 12 1500 watt RMS sub under control. Without it I get various room resonances and some slap echo from the wall my center channel is hung from. In-house versions of room correction by Sony, Yamaha and other Japanese companies are no where near the capabilities of Audyssey. My sub was out of control with a Sony receiver I briefly tried. Made the whole room resonate, especially anything metal. To me, Audyssey is a basic requirement, and Denon, Marantz, Integra, and Onkyo all use it. The only other option is to step up to Anthem and their ARC system. In the past I was a no-EQ purist - pick the speakers for the room and place them appropriately. This was fine when my house was on a slab, or before that when my college apartment was a half basement. When I moved to a house with a basement and set up the same components in the 1st floor living room, it sounded boomy as hell and I had to reduce the bass knob a touch. Before that the bass/treble tone controls were bypassed.

Seriously, almost everything you hear on a modern recording has been heavily processed. You can play an electric guitar direct into a mixing console, which will sound absolutely awful, and then run it through software to pretty convincingly make it sound like it's coming from a real amplifier, in a real room, into a real mic, onto magnetic tape - all of these factors have been modeled digitally now and you can select and adjust all of them. Voices are pitch corrected, drums are time corrected, and everything is EQ'ed.

And for all "true" 5.1 music, the sources are first recorded in mono with a microphone, then during digital mixing they are placed in the soundstage wherever the artist, producer, and mixing engineer place them. Before Dolby Atmos, it was more of a setting the level of the source in each of the 5 channels, now it's object based so you tell the system where you want to source to sound like it's coming from, and the system determines the levels for each channel.

My point is everything is a compromise and there is no "pure" audio that you are trying to perfectly recreate with your home system - it's all been heavily processed and modified in the studio before you ever hear it. Whatever you like the sound of is fine with me and should be fine with anyone else, unless it's so loud that it disturbs the neighbors. This is one of my primary disagreements with "audiophiles" - they seem to think that the sound heard by the mixing and mastering engineer is the holy grail and must be reproduced exactly the same. Except to hear that sound they would need to be in the same studio control room using the same studio monitors. In that case they might as well just buy a pair of internally powered bi-amped Genelec studio monitors and call it a day. No one in the productive stream before the audiophile cares one whit about "purity", other than to record in 24 bit and at least 96 KHz to ensure there is absolutely zero degradation of the sound during D/A conversion or mixdown to consumer formats. Everything else is molded into the artistic vision of the artist and producer.

The exception is if you are listening to symphonic music recorded in stereo in a concert hall with mics above the conductor's head, or acoustic music live in a room/club with stereo mics and minimal post processing. Anything else and you are listening to close-mic'ed sources all mixed into whatever image the artist/producer wants using modern methods. All "live" concerts start with a recording of all of the channels from the mixing console in parallel - 48 tracks (or more). Then they go through the studio mixing process to create the stereo or multichannel image, adjust EQ, fix mistakes (pitch, timing, whatever), add reverb and echo to simulate the sound in a big hall or stadium, and mix in a little sound from the ambient mics that recorded the crowd and the natural reverb of the location. Pink Floyd and David Gilmour are probably the best at doing this "more live than live" mixing.

This message has been edited. Last edited by: Lefty Sig,