Adjusting Subwoofer Phase <-- Awesome Bass, Part Deux!

In my prior post on Choosing a Crossover Frequency, I discussed the fundamental role played by a Subwoofer in any good, Home Theater system, and the equally important choice of allowing that Subwoofer to handle the lowest bass frequencies which would otherwise be played through the Main speakers.  This task of "steering" bass from the various Main speaker channels to the Subwoofer is the job of the Crossover processor -- part of the "Bass Management" system in your Audio Video Receiver (AVR).

The Crossover does not act like a switch, with bass suddenly cut off to each Main speaker and sent instead to the Sub.  Rather, the Crossover rolls into effect over a range of frequencies -- typically one Octave (factor of 2 in frequency).  So for example, an 80 Hz Crossover -- the most common choice -- actually rolls into effect from 80 Hz down to 40 Hz.  At 80 Hz, all the audio in the Main speaker channel is still coming out of the Main speaker.  At 40 Hz, all the audio is being sent to the Subwoofer.  And IN BETWEEN, the Main speaker and the Subwoofer SHARE the job of producing the audio output!

So in that critical range of in-between frequencies, a given Main speaker and the Sub are playing the SAME audio at the SAME time.  But the Main and Sub are not located at the same spots in your room, and the differing designs of the Main and Sub undoubtedly introduce different delays in how the electrical input signal to each turns into motion of their speaker cones -- creating the audio you hear.  The upshot is the audio waves arriving from the Main and Sub may very well NOT reach your ears at precisely the same instant of time!  The sound which SHOULD have blended perfectly from the two of them will not do so.

Technically, this timing mismatch is called Phase error, and it can be a real problem!  If the two wavefronts are a full 180 degrees out of Phase, for example, they'll CANCEL each other out!  That is, the result of improper Phase matching is anemic sounding bass.

In this post, we'll talk about how to get your Subwoofer(s) into proper Phase with your Main speakers.

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The Familiar Ring(ing) of Excess Sharpness!

The Sharpness control is one of the Basic Video Level settings found in every TV.  It is also, alas, one of the settings most commonly abused by manufacturers trying to make their TVs stand out in a wall of competing TVs under garish store lighting!  Indeed, TV Factory Default settings with Sharpness set WAY too high are commonplace --  a key facet of the justly-infamous Torch Mode settings foisted on new TV buyers. See my prior post on Extinguishing Torch Mode Settings for the others.

Excess Sharpness, in particular, produces the appearance of "false detail" in the image, which looks attractive on a casual glance (applause from the Marketing guys!).  However, the REAL details of whatever you are watching are ACTUALLY being obscured!

In this post we'll discuss what the Sharpness adjustment does to your image, and how to set this control properly in your TV -- using a Calibration Disc.

We'll also discuss the problem of "Edge Enhancement"; damage akin to excess Sharpness ALREADY baked into the content you are watching!

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Peak Whites Video, OR "Always Look on the Bright Side of Life!"

One of the biggest changes in a long time in Home Theater Video has been the recent introduction of High Dynamic Range (HDR) content, and equipment which can display it properly.    HDR allows elements in scenes to be much MUCH brighter than with prior home video technologies (in comparison to other portions of the same image) -- excellent for sparks, glints, flashes, direct views of light sources, and details in bright objects such as clouds in bright sunlight.  However, there is plenty of Standard Dynamic Range (SDR) content out there which you will still want to look its best.  And the foundation for understanding what HDR brings to the table begins with an understanding of the proper rendering of SDR Video.

In my prior post on Blacker Than Black Video, I introduced the concept of the Headroom and Foot Room portions within the video encoding.  The "Peak White" pixels found in SDR Video simply reflect the Headroom authored into that video content.  Whereas HDR and SDR Video are quite similar in their treatment of Blacker Than Black pixels, they differ dramatically in how they handle these brightest pixels.

In this post we'll focus on setting up your TV to render Peak Whites properly whenever you are viewing SDR Video content:  I.e., what you SHOULD see and what you SHOULDN'T see.  So break out the sunscreen and get ready for a few Bright ideas!  COOLNESS NOTE:  Shades are optional.

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Understanding DSD to LPCM Conversion, OR SACD "Noise Shaping" for Fun & Profit!

In my prior post on Digital Audio, I introduced two, "simple", Digital Audio formats:  LPCM (Linear Pulse Code Modulation) and DSD (Direct Stream Digital).  These are "simple" in the sense that each stream of LPCM or DSD contains the audio for just one speaker channel -- as compared to the more complex, Bitstream formats which combine multiple channels into a single stream.

However, there is one huge, practical difference between them.  DSD Digital Audio can not be "processed"!  If you have DSD content, and want to convert it directly to Analog audio for your speakers, without any other format fiddling in between, you most forego all types of Digital Audio processing.  So, no Crossover (bass steering).  No Down-mixing.  No Surround Sound processing.  No Speaker Distance adjustments.  No Room Correction.  NOTHING, except for Volume control.

If you WANT any such processing, you must first convert the DSD Digital Audio into a different Digital Audio format which CAN be processed.  I.e., into LPCM.

Which of course raises the question, "Is that SAFE?"  Can you DO that without screwing up the quality of the DSD original?  Or must you give up quality to gain access to that processing?

The short answer is, Yes, it is safe, given properly engineered gear.  Let's take a deeper look at what's going on!

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Blacker Than Black Video, OR "Hello Darkness my Old Friend!"

One of the Holy Grails of Home Theater (an avocation clearly overstocked with the darn things) is achieving the proper display of near-Black details in your video.  This of course starts with the proper display of Black itself!

It should be EASY, right?  As I detailed in my post on Digital Video, every format for Digital Video DEFINES a particular pixel value as representing "Black".  All the TV has to do is make that pixel, well, Black!  No light output.  And uh, brighter pixels should be brighter than that. Of course your particular TV might not be able to turn a pixel TRULY Black.  But that's a detail.  You get it as black as you can.

Then with a wave of my hand (something oft accompanied in the teaching game with a sotto voce, "Step 2:  A Miracle Occurs!") I mentioned there is ALSO a portion of the video data range reserved for describing pixels as, "Blacker Than Black".  Um, say WHAT?

Well, Bunky, it's time to get dark.  I mean REALLY dark.  So slip into your most Goth outfit, put on that sombre music, and lower the lights.  For we are about to encounter Blacker Than Black pixels, and learn what to do with them.  And what NOT to do with them!

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How Come Some of my Stuff Still Looks or Sounds So Awful? OR, That's Art from the School of Shoddy!

If you are serious about audio and video, know this:  The BETTER the quality of your audio and video setup the LESS forgiving it will be of crappy content!  ALL of the defects in your poorer quality content WILL now be seen and heard.

Upgrade your audio system?  You may find some of your favorite music tracks are no longer listenable.  Upgrade your video system?  You may find some of your favorite movie discs are no longer watchable.  And no amount of "enhancement" features in your electronics can "fix" such problems.  The creation of poor quality content results in a loss of information; a PERMANENT loss of information.  The most you can do for it now is "blur" the defects so they become less annoying -- at the risk of also blurring whatever's left that's GOOD in the content.

Things that strike you as odd or wrong in a piece may, of course, just be due to mistakes in the performance, or how it was captured, or in the authoring of the version you are playing.  Such mistakes do happen.  This is one of the reasons you want to confirm your setup using content of known correctness.   E.g., Calibration Discs.

You will also, from time to time, discover cases where the "Artistic Intent" of the material is simply not to your taste.  Just as with the story itself, and the acting, you may not like how the art and sound design of a piece are used to tell that story.

But that's not our topic for today.  Today's post is about trained professionals, intentionally doing stupid things because they thought they were a good idea!  This is Art from the School of Shoddy.  Let's check out the Curriculum, shall we?

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Understanding Audio Downmix and Surround Sound Processing, OR Wait! I've Got the Wrong Number of Speakers?

It used to be so SIMPLE, back in 1898, when Francis Barraud painted his brother's dog, Nipper, staring intently into the brass horn of a wind up phonograph and hearing, His Master's Voice!

One audio channel.  One speaker.  One dog.  And one enduring trademark!

One has to wonder how Nipper might react to today's Dolby Atmos installations for Home Theater (or any of its competitors); a technology designed to support up to 24 speakers at ear level, a special bass audio channel, and 10 ADDITIONAL "height" speakers overhead!  Would Nipper still stare in wonder?  Or would he dive under the sofa?

The answer to that question likely revolves around how INTELLIGENTLY those speakers were used!  In particular, what if the content you are playing has a different number of audio channels from the number the speakers you have installed?  This is the realm of audio Downmix and Surround Sound Processing, and that's our topic for today.

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A Field Guide to HDMI Failures. Collect 'em all!

It's still early days in my Blog, but here I am already, typing up my THIRD post on that wondrous in its Byzantine splendor, steam and string powered world of HDMI cabling.

Truly, if you are looking for things to confound Home Theater owners, and exasperate even skilled installers, HDMI is the gift that keeps on giving!  And I say that as someone whose history with digital video long predates even HDMI version 1.0!

Not the least of the problems is recognizing whether something going wrong in your setup might even BE an HDMI failure.  And in light of that, I present this humble Field Guide to HDMI Failures.

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Understanding Frame Rates, OR "24 Into 60 Won't Go!"

Movies and Television work because the brain WANTS to see continuous motion.  If you look at a sequence of still photographs, each changing just a bit from the photos before and after, and all flashed fast enough in front of your eye, your brain will blend them together into moving imagery -- an effect called Persistence of Vision.  You will no longer see the separate photographs.  You will see "A Movie"!  This trick, which goes back to the invention of moviemaking, works only if the images really are flashed past the eye fast enough. The question, then, from the very beginning was, "How Fast is Fast Enough?"

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Choosing a Crossover Frequency <-- Awesome Bass Begins Here

Much of the visceral excitement of Home Theater -- whether for movies or music -- comes from the proper rendering of Bass frequencies.  Unfortunately, setting things up to ACHIEVE awesome Bass is complicated -- almost to the point of being a Black Art!

But take heart.   As with many such complicated things, there's always a place to begin!  And with Bass audio, that means understanding why you need to include a Subwoofer in your speaker configuration, and learning how to select a Crossover Frequency to drive it.

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