| Video Noise June 2009
Your Home Theater's Sound:
Killing Your Highs?
 Managing
the high-frequency content of the video sources you watch or the music you listen to
isn’t typically covered in the owner’s manuals you’re likely to receive
with any of your home-theater gear.
Music recorded on CDs and other formats doesn’t adhere
to the same frequency-response standards as are used for films. Part of the problem is
that movies are mastered to be played in movie theaters. In such large spaces, the high
frequencies need to be boosted enough to be audible throughout the theater. This is
because high frequencies are more easily absorbed by theater seats and drapes, and by
people’s clothing, than are low frequencies, and are also more directional -- that
is, their sound is not as easily dispersed throughout a large space. If you were to listen
to that same movie soundtrack at home, there would be way too much high-frequency content.
Years ago, when the A/V industry was still sorting out the
differences between commercial and home theaters, some films were released with too much
high-frequency content for home listening. Today, however, most of the highs in the
soundtracks of the films you can buy or rent on DVD or Blu-ray have been balanced for home
theaters. Music-only recordings have always been released ready to listen to at home or in
your car, already balanced for listening in medium-to-small spaces.
Over the years, audio/video receivers (AVRs) and
preamplifier-processors have been manufactured with increasing numbers of settings for
modifying a system’s high-frequency response, primarily by removing 3-4dB from the
highs, beginning in the 4-6kHz range, like a filter in a crossover. What’s worse, if
your AVR or pre-pro lets you select more than one of these modes at the same time, you
might double or even triple your system’s rolloff of the highs, leaving you with
dull, flat sound.
(Note: Increasing or decreasing the volume by 10dB is
generally accepted as making the sound "twice as loud" or "half as
loud," respectively, though there’s no way to determine this precisely; the only
yardstick is human perception.)
A change in volume of 3-4dB is fairly significant and easy
to hear. If you want to experience movies without any extra HF rolloff, you need to know
what modes will potentially deliver that rolloff so that you can avoid them.
Re-EQ was an early attempt to provide a solution for
too-bright movie soundtracks. It works fine if you need it, but so few recent movies are
released with too much treble energy that I can’t recall ever intentionally turning
on Re-EQ for any movie I own or have rented.
THX modes are appearing in more and more AVRs and
pre-pros. THX contains a high-frequency rolloff that tries to make the sound of your home
theater mimic the HF balance you hear in a movie theater. It’s worth experimenting
with THX modes in certain circumstances. I tend to find them most desirable when I want to
listen to an entire movie at or near reference listening levels. Having that bit of
rolloff makes it less fatiguing to listen to. You may or may not like what THX does. If it
seems to dull your sound too much, just turn it off. I find that, at more reasonable
listening levels, I prefer to turn the THX mode off to experience the movie without
rolled-off highs.
Dolby Pro Logic IIx Cinema and DTS Neo:6 Cinema
both apply a high-frequency rolloff that’s easily measured and is obvious in
listening tests, once you know what’s going on. But both Dolby and DTS also have a
Music mode. Some may think Music mode a good substitute, because it shouldn’t include
an HF rolloff. But Music mode is intended to "expand" two-channel sources to
5.1- or 7.1-channel surround, and the Music modes of Dolby and DTS give different results.
Dolby provides a more expansive surround, while DTS simulates a concert experience, with
the music up front and the echo and ambient sound -- the sound of the hall itself -- in
the surround and rear channels. The Music modes of Dolby Pro Logic IIx and DTS Neo:6
really aren’t right for 5.1 or 7.1 movies.
The newest way you can unintentionally lose high
frequencies is with the Audyssey automated setup and room-correction software
included in more and more AVRs and processors. The standard Audyssey frequency-response
curve rolls off the highs in a way that Audyssey feels best replicates at home the
experience of watching a movie in a commercial cinema. Audyssey is available at multiple
levels; the more advanced versions tend to add more capabilities as additional options are
added to increasingly expensive AVRs or pre-pros.
AVRs also include controls -- equalizer settings, tone
controls -- with which a system’s frequency response can be adjusted. These are
almost always best left alone unless there’s a compelling reason to use them.
While some will find a degree of HF rolloff desirable,
others will prefer movies without it. The only way you’ll be able to know what your
preference is will be to actually listen to movies without HF rolloff. You might find, as
I have, that you want the rolloff only when you listen at reference levels (quite loud),
but prefer none at lower volumes.
What can you do?
Find out what your options are with your AVR or pre-pro.
Potentially helpful settings include:
- Some AVRs and pre-pros that include Audyssey also have an
Audyssey Flat mode. At a minimum, this should be enabled for music-only listening. But
with more and more movies on DVD being mixed correctly for home listening in the first
place, you may prefer Audyssey Flat for movies, too, especially if you’re going to
use a THX or Cinema mode that reduces the highs.
- Some AVRs and pre-pros include a control called CinemaEQ or
something similar. This mode will usually have only two settings: On and Off. Selecting
Off will disable the HF rolloff for modes whose names include "Cinema."
- Some AVRs and pre-pros have a "pass-through" input
mode for 5.1- or 7.1-channel soundtracks. This means you can listen to a movie without
using THX, Dolby Pro Logic IIx, or DTS Neo:6. The names given this "no extra
processing" mode vary: "Multichannel," "5.1," "7.1,"
etc.
- If you’re sending Dolby TrueHD or DTS-HD to your AVR or
pre-pro rather than decoded PCM, many AVRs and pre-pros will decode the bitstream without
adding any other processing or rolloff -- unless you manually select a Cinema mode from
THX, Dolby Pro Logic IIx, or DTS Neo:6.
If you’re lucky enough to have some of these features
in your AVR or surround processor, you may be able to listen to movie soundtracks without
any high-frequency rolloff. I’m not saying that a ruler-flat frequency response will
be right for every room and every system, but until you hear what it sounds like over the
course of an entire movie, you won’t know what will work best for you.
. . . Doug Blackburn
db@hometheatersound.com |
