Content and news by LD Blake

[PAGETITLE=Introduction][Top Ad] For the past few months, I've been working almost exclusively with multimedia PCs. In particular, the ASRock/Intel Atom-based computers that very nicely hook up to HDTV sets and new 1080p monitors. In several cases, these have been connected to high-end audio setups, incorporating some truly impressive gear... 100W channel, 5.1 is pretty typical of current setups. As the audio power increases, so does the risk of seriously annoying your neighbors. So, I went looking for a solution. But first, the problem. Music can be really annoying when it's not your own, but everyone knows that's pretty much a volume control solution that's enacted after unwanted attention from landlords or police. Despite the range of modern audio equipment, modern music usually has a very low dynamic range, so, simply turning it down usually fixes the problem. Movies, however, pose a somewhat different problem. The "soundscape" of a movie is very complex. There are bands of audio that can cover a dynamic range of at least 60dB, and sometimes more. This began with THX, a theatrical sound system inteded to give movie-goers an "experience" they didn't get at home. Over time, it's leaked it's way into retail DVDs, Blu-rays, and more recently, downloadable movie files. Generally, a movie has its peak audio devoted to sound effects. We'll call this 0dB for reference. Dialog tends to be inserted at about -20dB (yeah, that's a lot quieter), and some of the foley (term for post-production sound effects that enhance the soundscape for a more immersive environment) events such as rustling papers or footsteps begin at about -40dB. In simpler terms, the range between softest and loudest sounds in a single movie can run from barely audible to unbearably loud. Credit: Mike Golding In an average living-room, the background level (traffic noise, refrigerators, furnaces, air-conditioning, et cetera), is generally around 20 - 30dBA (acoustic decibels as heard by the human ear). To hear the foley effects in a movie, you need to get them above that level, generally around 25 - 35dBA. This means that your average DVD movie can produce peak sound levels beyond 80dBA, which is far too loud to talk over without shouting. And this with the movie turned up just enough to hear the low-level foley effects... never mind that most people crank it up even more. Further, you should note that decibel scales are logarithmic. If 30dBA requires 0.1W of power, 80dBA would require about 150W... 1500x the power, and that's going to be very loud. THX makes this problem even worse because it adds the BIG sound... use of infrasound (frequencies under 100Hz) to give a sense of power and presence in movies. This sound is almost unheard, but when correctly used, it can invoke powerful emotional responses in an audience. It's about the pitch of the sound, the context in the movie and the levels used. It takes a lot of power to reproduce sounds this low in pitch. Often, the BIG sound is the highest level audio on a DVD, even though you don't actually hear it as a discreet sound - and unfortunately, it goes right through walls like they aren't even there. When removed from context, this BIG sound becomes a booming, thoroughly annoying noise in your neighbor's home. If you're interested in hearing some of what I'm talking about, you can get some THX demo pieces here, and you can read more about infrasound here, or do some quick Google or Bing searching. It's a truly interesting field of study. The problem is that in order to hear the quieter parts of the movie, which often includes spoken dialog, you have to turn the volume up tot he point where louder parts are positively deafening, invoking the wrath of your neighbors. This is especially true when you live in an apartment building and have eight other homes only inches from your own. The solution needed involves three parts. First, you need some way of limiting the maximum volumes so that you're not blasting your neighbors. Second, you need to boost lower-level sounds so you don't have to turn up the average volume to hear everything. Third, you need to address the THX BIG sound. [PAGEBREAK][PAGETITLE=The Solution] The software to fix this problem is the AC3Filter (by Alexander Vigovsky) which can be downloaded for free and works on all Windows platforms. But simply downloading and installing this software won't fix your problem. You will need to do some experimenting and adjusting on three sections of the filter software to get a working solution. You will need to set up a volume limiter, a dynamic range control and also adjust the equalizer. To get started, you need to install the filter and do the basic setup. Once installed, open up the AC3Filter configuration dialog (from your Start > Programs menu) and click on the System tab. On this dialog, and in the upper-left corner, you will find a list of sound formats to be processed by the AC3Filter. You want to check them all since they are all found in various movie files. Also, be sure to set the filter's merit to "Prefer AC3Filter" to ensure it's always activated. If you don't want it to disturb your system's sound levels (eg. move the sliders in your mixer applet), be sure you check the "Use Direct sound by default" box. Now, on the Main tab, set the upper-left corner to suit your sound card. Most cards today will support 48KHz 24-bit audio, and some will even go as high as 96KHz and 32-bit. These should be set to match the capabilities of your sound card. You might as well set the filter to up-convert your files, which will often yield a noticeable improvement in sound quality. Other settings allow you to redirect sound to SPDI/F and HDMI outputs. These will need to be adjusted to your system requirements. At this point, if you've checked the box for "Show tray icon" on the System tab, you should be able to play a movie and watch the filter working by clicking on its icon. As the movie plays, you will see the level bars reflective of the various sound levels on each channel of your sound system, on the Mixer tab. Take note of the differences between effects (explosions, gunshots, etc.), dialog (people talking) and foley sounds (rustling paper, crickets, rainfall, etc.) and you will see the various audio bands in use. Now, to fix our complaining neighbor problem. First, you will need to set up a volume limiter. The AC3Filter documentation does a poor job of explaining this, so I hope I can do better. The idea is to drive the overall sound level up to the point where the filter's limiters are triggered by sounds in the effects band, thus limiting the difference in loudness between dialog and effects. On the Main tab of the setup dialog, set the Master / Gain control to about +12dB. This will effectively increase the dialog and foley bands of the movie to be about three times as loud as normal, without increasing the levels of the effects band, which is driven into the limiters. On the Mixer tab, make sure you check the "Auto gain control" and uncheck the "One-pass norm" boxes. This automates the limiter so that your volume levels for high-level sounds remain more or less constant throughout the movie. If you do not uncheck the one-pass option, you will notice that movie getting quieter and quieter with each successive loud sound. The auto gain function, as set, causes the audio levels to recover between loud sounds. Also on the Mixer tab, check the "Auto matrix" box and uncheck its sub-boxes. This will prevent uneven effects without altering your speaker setup. Second, you need to set up a dynamic range control to boost the foley sounds to a certain degree. On the Main tab, in the DRC (Dynamic Range Control) section, check the "Enable" box and set the left slider to about +8dB. This will have the effect of boosting the quieter parts of the movie to almost twice normal loudness. Like the auto volume control, this function also automates so that the gain of lower-level sounds is automatically adjusted throughout the movie. On the System tab, you may need to adjust the attack and release times of the automated level controls (DRC and Auto Gain). To even out the average levels somewhat, you want a fast "attack" time and a fairly slow "release" time. In the AGC section, you will see the filter defaults to 100 and 50dB per second. Setting the release (second) rate to 20dB/s will significantly even out the reproduction of the dialog band of the movie. Third, you want to limit that BIG sound. On the Equalizer tab, set the presets and sliders as shown in the images below. Of particular importance is cutting the 30Hz band quite deeply, so -8dB should do nicely. Next, you want to cut the 60Hz and 125Hz bands by lessening amounts to smooth out the response curve. The settings shown will lower the levels of infrasonics (BIG sound) to about half the normal (and don't forget they're often driven into the limiters as well). You probably won't notice this without using test equipment. Sounds at these frequencies are more felt than heard, and still produce a noticeable effect, even with cuts this deep. The result? Decent movie sound at much lower volume settings. No, this isn't the big powerful home theatre setup you've dreamed of. But, with the settings as details, you will still have a dynamic range of at least 20dB which is more than enough to enjoy a movie, and since you will able to hear everything with lower volume settings, you won't have your neighbors banding on your door. The starting points given are a compromise between THX's wild dynamics and the lifeless sound of old TV shows. Over time, you can fiddle with these settings a bit to customize them for your own installation and preferences. If you are wondering whether or not adjusting your sound this way will effect the overall quality of your movie, it will, but not to a great degree. For some, it likely won't even be noticeable. I've drawn up a little chart showing the approximate levels of various...

Content and news by LD Blake

Managing Your Audio to Keep Neighbors Happy