SME

If and when the time comes, I will do just that. Even now, I can measure and roughly extrapolate using the equipment I have now. Things get rough below my 12 Hz mode, and I don't see any evidence of room gain in the 8-10 Hz range. A quick calculation suggests that even if my room is perfectly sealed, I need 8 X18"s to get enough displacement to hit the room gain limit with enough output to matter. In the long term, I hope to add-on to my house and build a custom sealed room. I should just save my money to get that build sooner.

Single sines may be rare, but sine sweeps appear all used quite frequently. The distortion measurements I reviewed were obtained using sine sweeps anyway. Distortion results from non-linearity of the driver parameters such as motor strength, inductance, or suspension compliance. If the non-linearity is smooth and the input signal consists of a single sine wave (or sine sweep), the distortion will be purely harmonic. If the input consists of multiple sine waves then Inter-Modulation Distortion (IMD) results. IMD contains both harmonic and anharmonic overtones. The anharmonic overtones from IMD resulting from two simultaneous sine waves are likely to be even more audible than the harmonic overtones from a single sine wave. Both THD and IMD arise for the same reason: smooth non-linearity. This means that if a tone contributes high THD in isolation, it will also contribute high IMD when played with another tone. Realize that these 2m ground-plane distortion measurements are done with constant voltage input. Even with constant voltage, sealed subs show increasing THD with decreasing frequency. This means that even if you have a perfectly sealed room with 12 dB/octave room gain to cancel the sealed roll-off, there will still be a general trend of distortion increasing with decreasing frequency for the same in-room SPL. This trend appears to be consistent with just about every sealed system measured on data-bass. Another trend I see is that as drive voltage is decreased from that required for peak output levels, the distortion doesn't decrease as quickly for low frequencies as it does higher frequencies. In fact, it looks like the distortion may approach a minimum level that may be as high as 10% or higher for most woofers. Here, I'm specifically talking about performance well below 15 Hz. Unfortunately, the data-bass sweeps don't go lower than 10 Hz or -15 dB from the peak output voltage, so I can only guess as to what happens at lower levels. On the other hand, it doesn't matter as much how the woofer performs much below -15 dB from its peak since the audibility threshold of ULF itself is so high. One last trend I see is that the distortion at the bottom end is mostly 3rd or otherwise odd order in nature. This increases the likelihood of audibility, and it also means the 2nd harmonic is not a good measure of overall distortion. I'm not certain of this, but I think these trends arise because the influence of the suspension increases as frequency decreases, and the suspension is the hardest part to make linear. It is the relative symmetry of the suspension with respect to in-vs-out strokes that makes it dominated by odd harmonics. The example you give in EOT is an odd special case. Although multiple frequencies are present, they all share 10 Hz as their fundamental. As a consequence, the IMD overtones are also harmonics of 10 Hz. In this case, I would not be surprised if the 20 Hz and 40 Hz overtones are substantially stronger than they would be with 10 Hz playing alone. This is because of its IM character. On the other hand, the source material has such strong odd harmonics that it's impossible to see how much 3rd HD the sub is producing. That passage might sound okay, but another passage with 10 Hz at the same level but lacking that strong 3rd harmonic might still sound like the EOT effect even though it's supposed to sound much more clean. I don't doubt the substantially enhanced experience offered by a system capable of high output ULF. You must realize, however, that the cost for me will exceed what I've spent for all the rest of my equipment, and I already get very clean reference level performance down to 20 Hz in an open living room. Sound quality is very important to me, and I only want to spend that money once if possible. As a rough figure, I believe most people can detect 5% THD in music. In the upper ULF region, the ear's sensitivity has a very steep slope, and as a consequence, the distortion overtones are likely to be much more audible than they would be if the distortion occurred with full-range music content. As such, the audibility threshold may be much lower for "musical" ULF. By quoting "musical", I'm noting the fact that actual ULF sound effects are probably more likely than music to consist of odd order or otherwise noisy overtones. It appears that this feature of sound effects masks a lot of the distortion produced by subs in the spectrograms. What's not clear from these spectrograms is if the distortion causes significant phase alterations and whether these may be audible. Also, for particular passages that are especially heavy on the noise (very common), the spectrogram may make it difficult to spot flaws that may actually be audible in reality. The distortion noise will have a lot more structure and potentially more acoustic coloration than the pink noise that masks its appearance in the spectrogram.

Yep. Ignoring leaks, in the low bass limit, I expect you have ~11 dB more output than I with the same equipment, and unfortunately, I have a full basement for my "room" to leak into. That's fairly consistent with my estimate that I'd have to spend ~3-4X as much money to really "get there". I don't really consider tactile transducers a solution. While I think they can enhance the listening experience if deployed with care, I prefer air-borne sound to provide the majority of the sensory experience. My point about distortion is that almost all sealed box designs have relatively high distortion (particularly 3rd harmonic) when playing ULF even at moderate levels (e.g. 5-15 dB below mechanical limits). At such levels, the distortion isn't high enough to fail the CEA test, but it may be high enough that for example, when a 10 Hz sine is played at a below threshold level, you still hear the 30 Hz 3rd harmonic. On a system with low distortion, a 10 Hz wobble that fades in gradually may scare the life out of you when you suddenly perceive something that was lingering there all along, but if that 30 Hz harmonic is strong enough, it might tip you off as to what's coming and make the effect a lot less dramatic. Before I spend the big bucks on a ULF system, I'd like to try to solve the distortion problem. Rotaries do the trick, for those with $25k and an adjacent room to use as an air reservoir (not me on either account). For now, I'm more focused on getting good sound > 15 Hz.

You got to single digits for only $2250? What kind of room volume are you driving? I am unfortunately in a living room that opens to the rest of the house at 9000 ft^3. My first room mode is around 12 Hz, which is great for getting significant output down there from my 16 Hz ported subs. Recently, I did a bit of research and considered a few different sealed sub array configurations to get to the single digits. At this point, I only have a rough guess as to how much displacement I'd need for this room, but it looks like I'd need a lot. Even a "starter" system, which may not do appreciably better than what I have now with ported subs would run me more than $2250. To get real good performance, I'd likely need to double that figure. Then there's the labor. Nevertheless, I got very close to buying. The issues that held me back were (1) that the woofers I wanted most were from a company with a very unknown future, and (2) distortion! I compared the distortion figures measured by data-bass for various sealed systems versus the ported subs I already own to see that I'd need to spend extreme $$$ for that extra octave in order to enjoy the same distortion I do now in the 15-25 Hz range. It's one thing to get high CEA number, but to be able to play deep bass with single digit THD% at levels not much further down is a big deal! In principle, distortion is even more audible in the ULF range because of the great differences in our hearing sensitivity for fundamental versus harmonics. I decided that when I do go for the single digits, I'll keep all the subs I have now and crossover the 16 Hz ported subs somewhere in the vicinity of 18 Hz. Having already developed a room-optimized custom crossover between my deep bass subs and my mid/upper bass subs, I'm quite confident I'll be able to integrate the ported subs with a ULF sealed array. That configuration will seriously rock because I can run the ULF a bit hotter into a limiter without compressing or distorting the rest of the bass. I will also avoid the nasty IM distortion that comes with playing higher frequencies on a woofer that's undergoing heavy ULF excursion. I will have a tri-amped bass system (or quad amped, if you count the upper bass provided by the mains and their hefty amp)!

About clipping and loudness: I don't like it either. After discussing it earlier in this thread, I am of the opinion that it's best to leave the current bass rating system as is and address clipping and loudness with qualitative comments. I do think quantitative loudness ratings would be very helpful. I may attempt to do this kind of analysis myself at some point, but it will be at least a few months as my attention is currently on other things.

This pattern has nothing to do with a house curve being embedded in the mix. To the extent that this may have been done, it is unlikely one can tell by looking at a PvA. Instead, what you see in the PvA has more to do with the fact that loudness perception drops off rapidly with decreasing frequency in the sub bass range and also the fact that many natural broadband sounds exhibit an increase in level with decreasing frequency. For example Brown Noise increases at 6 dB/octave as frequency decreases. From 30-40 Hz to 130 Hz is about 2 octaves, so a 12 dB difference is, in fact, very reasonable to expect.

Earlier today, I ran "The Matrix" with BEQ. Before giving my impressions, let me describe my system. I'm running two subs ported at around 16 Hz and two (quasi) near-field mid-bass modules. All told, I am flat down to 20 Hz, -3 dB at 15.5 Hz, about -13 dB at 12.5-14 Hz, which is what I consider to be the audible lower limit. Note that the infrasonic response figures are very rough as room influence and seat-to-seat variation is very strong. The seat right of the MLP is only actually -10 dB at 12.5 Hz. Using this response curve, I have enough headroom to handle just about any existing program material played at reference level. My system is calibrated so that at "0", a -20 dBFS sine sweep plays at 85 dBC in the bass and gradually drops about -6 dB from 120 to 20000 Hz. Using this target curve helps tame the strong high frequency dynamics my system and room provide, which reduces perceived loudness and brightness and makes most sounds including dialog more natural and intelligible. I played the DVD as I don't own the Blu-ray yet. (It is rumored that Dolby Digital tracks are high-pass filtered at around 16 Hz. I personally have not seen evidence to back up this claim, one way or the other.) I started playback at -6 dB master volume but eventually adjusted the MV all the way up to "0". I noted that the track has a Dialnorm value of -4, so assuming they are otherwise the same masters, one would have to play the Blu-ray track at "-4" to achieve the same playback level as "0" on the DVD. I usually use dialog to judge what playback level is most appropriate, and at my chosen playback level, the dialog sounded about right if not a bit quiet. Overall, I think the BEQ improved the listening experience, but the improvement was not as much as I was hoping for. The BEQ does its part to bring out the bottom end, when it's there, but a lot of sound effects seemed to be completely lacking in the bottom end or even lacking bass entirely where I'd otherwise expect to hear it. Here are comments on specific sound effects, in roughly chronological order: In the first part of the movie, I noticed little change with BEQ. The bass section in the score was a bit stronger and the wind outside the building were Neo works had a bit more force, but that's about it. Unfortunately, the truck at the very start didn't see any benefit, but I think it was lacking in mid-bass too. The thunder definitely sounds much better with the BEQ! I like the infrasonic ambiance on the ship. I like the atmosphere it lent to the scenes. Of course, I have a roll-off below 20 Hz, so foor those with more extension, that sound effect may be excessive. The difference with BEQ was pretty subtle until the sparring in the dojo between Morpheus and Neo. Among the biggest bass hit in the movie is when Morpheus bashes a hole in the floor with his knee. It is strong enough to perceive without BEQ, and I'm guessing it is responsible for the 14 Hz peaks in the PvAs. Despite the considerable boost in level this effect got, I don't think the BEQ improved things here. The trouble is that there's little in the way of higher harmonics to reinforce the 14 Hz and give it definition. Had it been coupled with some good mid and upper bass slam, I could have accepted that he just put his knee through a floor, but it was not to be. I also thought the effect was too disproportionate to the others. There were plenty of other martial arts moves depicted in the film that should have thumped us a lot harder than Morpheus putting his knee through the floor. Oh well. The bass continues to run thin through the the scenes that follow. As the heros flee the ambush after Neo visits the oracle, some gas canisters provide a surprising thump when they are lit that sounds rather out of place against gun shots that are largely void of bass. I note little change in the fight in the lobby. The elevator bomb seems to have a bit more rumble. The helicopter sounds weak. My system can't really produce a well-defined helicopter blade fundamental, but I usually notice the pressure build if nothing else (just like I do when the real ones fly over my house). Here there is nada, but then it gets a lot better. The scene where the helicopter crashes into the building is the audio highlight of the film, and I think the BEQ made a massive improvement! Before, it always sounded a bit held back, like the sound is overloading or something. With BEQ, the thing really pops! It actually sounds like it looks like it should sound! This scene may be reason enough to use the BEQ. From here on, the bass remains quite good. Hand to hand fighting provides plenty of deep thumps and slams. The sound of bullets moving through the air in slow motion is very palpable. The synergy between the deep bass bursts and front-to-surround pans is excellent. The sentinels *do not* walk softly upon the hull of the Nebuchadnezzar. I must say, they don't look as heavy as they sound! The EMP blast provides one more good low-frequency harrah! In all, I think the BEQ improved the presentation, but I also think it brought to light a lot of flaws in the original sound design. This is to be expected when reversing filters as those filters tend to hide flaws from the engineers doing the production work. For all the great bass brought out by the BEQ, I was very disappointed that so many sound effects were completely lacking. Despite the much improved PvA, the movie still sounds bass shy to me, simply because so many moments were missed by the sound designers. It's still a great soundtrack considering when it was made, but it does reveal how far we've come since then.

No problem, and thanks for doing what you do here!

Harry Potter 6: http://data-bass.ipbhost.com/index.php?/topic/12-the-low-frequency-content-thread-films-games-music-etc/page-79#entry2055 Harry Potter 7 part 1 and 2 (scroll down): http://data-bass.ipbhost.com/index.php?/topic/12-the-low-frequency-content-thread-films-games-music-etc/page-82#entry2203

It sounds like it's not worth looking at BEQs you've already done. How do you actually verify that peaks remain < 7.1 channel dBFS? I think you'd need to either simulate the filters in software or sample the output of the NanoAVR when driven by the film audio. Then combine all channels (with +10 on the sub), find the peak value, and verify that it is within the correct limit. I agree with you that the nanoAVR is better for BEQ than using an EQ on the AVR outputs. Of course, I don't own one and don't anticipate buying one for a while. I prefer the MiniDSP 2x4 and recently acquired 3 OpenDRC-AN units to the nanoAVR because I am using them for room correction. I believe the nanoAVR is flawed for room correction, but clearly it is in the better place in the signal chain to re-EQ original sound tracks. As for headroom, it does not make sense for me to implement the gain adjustments you suggest for each EQ. In fact, it makes me more likely to clip my AVR output when trying to compensate using the master volume. This is probably true for anyone using device(s) that EQ bass-managed output. That doesn't mean that I don't have to worry about clipping at all. However, I can easily prevent it by not turning the master volume up too high, which doesn't work when using nanoAVR. For me, this would be avoiding MV > -3 without monitoring. Thinking about it a bit more, I believe I may have full 0 dB 7.1 channel FS headroom in the sub-out chain, so it's just the AVR that can clip, and if I implement BEQ in the post-processing chain, my AVR won't come into play at all. Whether my subs have enough headroom depends entirely on the signal. For most of the range, the amps have soft-limiting, which limits distortion a lot. I estimate my "clean" upper bound on output to be at least ~120 dB for most of 20 Hz and up, based on CEA data, my minimum-phase room response, and my EQ filters. I put quotes around "clean" because I'm not sure how to properly measure distortion in-room. When I recently experimented with CEA test tones and the RTA in REW, I noticed that the noise level (the "N" in THD+N) was much higher than expected, presumably because my house was making such a racket as it shook. What I should have done but didn't was to look at SPL to see power compression because my sub amps soft limit above 30 Hz or so. I have excellent room gain between 20 and 30 Hz. Where I'm most at risk is in the 10-20 Hz range because my subs are ported. I use an infrasonic low-shelf filter in my custom EQ to protect them. I chose the gain (-2 dB, IIRC) by assuming I won't be playing a signal with concentrated 10-20 Hz energy at higher than roughly -10 dB 7.1 channel FS at reference. I actually used data from this site to come up with that figure. So far, this has been a good compromise. I'm flat to 20 Hz and get audible extension to 12 Hz, yet I don't notice any playback issues. I tend to be extra careful with films that approach this limit, but with most of these, I find "0" to be too loud for my preference anyway. With BEQ (and perhaps the movie EoT), this may change. I do recall enjoying "The Matrix" at closer to "0". Apart from the weak bass, it has a very nice dynamic soundtrack. I imagine it will sound incredible with the deep bass restored. I am wary of that big peak at 14 Hz. Is that in the dojo sparring scene between Morpheus and Neo? I think I've noticed it, just barely, even without BEQ. I will definitely proceed with caution!

I don't have a NanoAVR, but I do have EQ capability for my sub output. I am looking forward to trying the BEQ posted for "The Matrix", when I get the time. I do have a request. Instead of merely reporting on those examples with peaks > 7.1 channel dBFS, can you give us the actual peak value, relative to 7.1 channel dBFS? For example, I currently have about -3 dBFS headroom, so if the BEQ version of "The Matrix" hits 7.1 channel full-scale at reference level, then I will need to play at -3 to not clip. Hopefully it's not too much trouble to add that information.

I haven't seen "Helloboy 2", but "9" has moderately strong deep bass from start to finish. Most of the strong deep bass coincides with generous mid bass and plenty of sound in general so that the shaking of one's house might be much less noticeable than pure tones against a quiet background as in EOT. Also, responses vary considerably from room to room depending on where one's resonances lie. The extended duration pure tones will tend to be most unpredictable because they can potentially excite very narrow resonances that lead to very strong strong peaks or nulls. In my setup, I don't get much wall/house shaking at all, but the deep bass is still unmistakeable because I feel *myself* shaking. I do have a floating wall (not attached at the bottom) between the interior of my house and the garage, which has a strong bending mode at around 15 Hz. It is strong enough that you can actually see the whole wall wagging back and forth. While it's novel to see happen, that effect isn't really a part of the movie. As time goes on, I'm finding that the less influence my surroundings have on what I hear and feel, the more immersed I am in the actual film. Each to their own of course.

That opening scene in "Edge of Tomorrow" looks like a sub-wrecker if I ever saw one! That 10 Hz tone may even be loud enough to hear on my system with 16 Hz, HPFed ported subs.

I noticed "Despicable Me" (the original) hasn't been measured yet. The wife and I watched it last night and enjoyed it immensely. The sound design is among the best I've heard. It has great slam and micro-dynamics from the bass to the treble. I also didn't hear any clipping or evidence of heavy compression. That doesn't mean it isn't there, but I usually hear at least some trouble in other releases. This one sounds very clean. The mixers used strong macro-dynamic swings skillfully to make things sound very powerful. Subjectively, I think it was a "Level 4" or "5" movie, but I wouldn't be surprised if it measures as a "3". I don't know how low it goes, but I definitely heard a lot of effects below 30 Hz and down to the limits of my system (15 Hz-ish). Oh yeah. This one has rockets, and they sound great! This is a good example of using strong bass dynamics and ULF to give the impression of very high acoustic power instead of using clipping or distortion. In any case, I look forward to seeing the sequel, which I see has been measured here and appears to retain the same positive qualities that I heard in this one.

http://www.digido.com/component/phocadownload/category/15-demos.html?Itemid=64 I had to register on the forum in order to get access to the downloads. I didn't have a problem with that though. The site is by Bob Katz who is a highly skilled and influential mastering engineer. He has also been a staunch advocate for high dynamic range in music releases. His focus is on music, but I wonder if he'd take an interest in the current apparent trend of increasing loudness in home film releases?

Shame! Even at -10, this thing will likely sound very loud and fatiguing. I gather the theatrical version was quite loud and probably took advantage of the headroom Atmos provides, and then they boosted it further for the home mix. It's so sad that many of today's headline releases have worse sound than some stuff done in the 1980s. By the way, I recently learned a couple reasons hard limiters at levels just below digital full scale get used: Some DACs behave very badly when presented with digital full-scale signals. Some may even repeatedly invert the output signal. Lossy compression can sometimes introduce just enough boost to cause a nearly-full-scale signal to become full-scale. See above. As such, it seems to be a very good to add a hard limiter somewhere slightly under digital full-scale.

These figures are very close to my own observations. I used the relative input level indicator on my MiniDSP 2x4 along with its published specs to deduce a max output voltage for my Denon of 4.0V rms. I also installed a few extra attenuators on the line and turned on a sub to hear the clipping. Right at -3.0 dB from the point at which the output saturated, clipping became audible, and it became much more severe with each 0.5 dB increment. Having done a lot of computer music in the old days, it sounded exactly like hard digital clipping. What surprises me is that you have to use the minimum trim of -12 to not clip a 7.1 channel digital full-scale signal at master volume "0". Even then, Audyssey may boost the signal at certain frequencies and still cause clipping. By your numbers, someone running with the sub trim at "0" and master volume at "0" will clip above 113 dB, which is less than digital full-scale on the LFE channel alone. In my current system configuration, I have meticulously EQed my subs to be as flat as possible across the listening area using my MiniDSP so that Audyssey is not tempted to boost anything too much. It mostly works, and thankfully soundtracks aren't pushing digital full-scale in all 7.1 channels just yet. The sad thing about all of this is that all they had to do was give up 2 bits of fidelity (probably at a level way below the noise floor of any realistic listening room) to get back 12 dB more headroom. If they let you set the trim well below -12 dB, then there'd at least be a work-around. Judging by what I read in other places, I bet some other AVRs are even more headroom limited than the Denon/Marantz. It'd be nice if review sites could report on stuff like this instead of talking about how much warmer AVR "A" is compared to AVR "B". Ugh.

An important point about clipping in playback equipment deserves mention. While we often think of clipping as occurring in the power amplifier, clipping can occur just about anywhere in the signal chain. Provided that the DSP arithmetic is handled properly, clipping should not occur during the bass management process in the processor/AVR. However, depending on the playback level and the amount of gain on the equipment downstream, the summed signal may be enough to clip the output DAC and/or the pre-amp output. This is absolutely the case on my Denon 3313CI AVR, which appears to implement the level trims in the digital domain. In order to maximize my bass headroom, I adjust the gains on my subs until the correct level trim for calibrated playback is as low as possible. I actually have my level trim at about -9.5, which is +2.5 above the minimum, so I can decrease it a tiny bit if need be. I forget how much bass headroom that actually gets me, but IIRC it's near 120 dB rms. Someone running with the sub trim near "0.0" would hit clipping at around 110 dB of output, which is quite low by sub standards!

I'm a bit late to the party, but finally watched OHF. (Warning: minor spoiler ahead.) Of all the captures on the site, the Washington monument scene is the one that threatened to do the most damage to my pair of Hsu subs. When listening, I played back at -6 dB, but will test my limits carefully with higher levels in the morning. In any case, I was very surprised by the effect. From the scene description and the trace, I assumed I was going to get a lot of trembling and shaking from bombs exploding or something. Instead I got a series of tight yet powerful crunches that I felt from my head all the way down to my gut. Color me surprised, but it sounded exactly like I'd imagine large slabs of concrete to sound like while buckling and splitting apart! It reminded me of the sound of the Bridge of Khazad-dum crumbling in Fellowship of the Ring, except with a whole lot more power and bottom end. I'm also happy it came out so clean from my subs, albeit at -6. While I didn't care for the movie that much, the soundtrack was superb. The explosions were great. Very tight and full-bottomed bass. Edit: On second watch, I'm not sure I would describe the Washington Monument scene of Olympus has Fallen scene in the same way. This time, I noticed more of what I expected -- a sense of continuous erratic trembling. Perhaps the higher playback levels brought the deep bass out more and made it sound less tight. In any case, the scene is still quite impressive. At "0", my woofers were moving pretty vigorously. Without the -3 dB shelf I have below 25 Hz, that scene probably would have been too much.

Thanks. This seems to provide some evidence (albeit anecdotal) that the soundtrack was damaged during production of the "at home" version. I believe that a remix or remaster for home release is done more often than not these days , and I have a strong hunch that a lot of clipping is introduced in this process. I have several earlier posts about reference level along with the speculation that many discs ship with hotter tracks, intended for playback at lower levels. In that discussion it became clear to me how fragile a concept "reference level" is when consideration is given to variance between rooms and systems. I was pointed to industry specific recommendations that lower monitoring levels be used in smaller rooms. In this particular example, a table was given specifying monitoring level to use for a particular range of room sizes. My assumption here is that the "at home" soundtracks are often monitored at lower playback levels, in accordance with these recommendations. If someone with additional knowledge knows otherwise, please speak up! Here's how I propose this might happen. Note, this is still speculative: The "at home" soundtrack is monitored at a lower playback level. I think commonly used adjustments include -3, -6, and -10 dB. At this lower playback level, the loudness is closer to that of the theatrical presentation than at "0 dB". However, the bass is very weak. Why? My thinking is that when comparing rooms, bass loudness does not vary as much as mid-range and especially treble loudness. I wouldn't be surprised if room size is irrelevant for bass loudness under 100 Hz. So when the monitoring level is reduced by 6 dB, guess what happens? The bass gets boosted to repair the tonal balance and restore the awesomeness of the big bass scenes. Where the track contained signal approaching digital full scale, clipping is very likely to occur. I reckon that in many if not most instances, the clipping is noticed, and different strategies are employed to remedy it. One option may be to redirect some bass from a busy front channel to LFE, This essentially preserves the signal but may not always work and be labor intensive to do. Another remedy may be to install a compressor or soft limiter. This limits dynamics but can give a very good result if done skillfully. Naturally, better results often require for labor. Still another may be to filter out infrasonics because they eat up a lot of headroom and it is assumed (probably correctly) that the vast majority of listeners won't hear them anyway. I'm sad to say it, but this remedy is likely very easy to implement. Being a low hanging fruit, I wouldn't be surprised if ULF does sometimes go out with the "at-home" mix, even it probably gets stripped for many theatrical soundtracks too. In the worst cases, I imagine some production may be too rushed to fix the clipping completely, or the monitoring system may be too poor to reveal it. The egregious cases like "Star Trek: Into Darkness" and "Godzilla" may involve mixes that were very loud to begin with being monitored at close to -10 dB. If the sub bass is to be boosted 10 dB a lot of work will be needed to make it sound clean, and if they're rushed, they might just throw a subsonic filter on it and hope for the best. If I had any influence, I would encourage studios to do their "at home" mastering at "0" and to reduce the level of the soundtrack itself in order to adapt it to their listening environment. Since almost all changes to the sound would involve reductions instead of boosts, there would be little chance of running out of headroom and clipping. Ideally, they would also use an EQ curve optimized for their room, but I'm not aware of any suitable model or standard that specifies what target curve to use for any particular set of circumstances. In reality, the correct target curve for a room depends on a lot more than just room size. If bass loudness may be assumed to not vary much between rooms, then it makes sense to calibrate bass responses the same and then shape the rest of the target curve using bass @ 0 dB as a reference. Then ideally, all rooms with optimized target curves and calibrated bass will sound similarly loud at "0". Lacking such a model or standard to go by myself, I recently spent a period of weeks making small adjustments to my own EQ target curve and listening to achieve a balance that "sounds right". While I'm not yet convinced I have it right where I want it, I am very happy with the curve I am using now, in which the treble is reduced 5 dB relative to the bass. It sounds much more balanced and natural than a flat response ever did. I am calibrated so that I get theatrical level bass at "0". If I got the curve right and if bass loudness doesn't change between rooms, then theatrical tracks should sound just right for me at "0". Thus far, most of the Blu-rays I've watched sounded "right" at "-3" or "-6". I believe this is entirely consistent with the idea that Blu-rays are monitored at lower playback levels and then re-mastered to sound equally loud to the theatrical mix, and that this change almost always requires a bass boost on the sound track. So there's my largely unsupported argument. I wish there was a way to get better insight into this. Clipping affects the listening experience for more than just those with high performance gear. I fear that even if studios were to recognize the headroom benefit of mixing at "0" all the time, they would be reluctant to do so for the same reason CDs often get compressed to death: they fear customers complaining about the "weak soundtrack" on the new release, all because it's not as loud as their other flicks when played at the same "volume setting". There may be justification for this. I recall that "Elysium" was criticized for having weak dynamics, when in fact that opposite was true. What was really going on is that people were equating maximum loudness with dynamics. By virtue of being so dynamic, "Elysium" needed a playback level to reach the same loudness. Unfortunately, 25 years of highly compressed popular music seems to have altered cultural preferences to be more in favor of a louder, more compressed sound. For those of us who appreciate realism in audio, I certainly hope this trend turns around soon.

Anyone see Godzilla in a theater with decent capabilities? Clipping that bad would almost certainly be audible in a movie theater, provided that it isn't running out of headroom for those passages. I know audio memory isn't very reliable, but I'd really like to figure out where most of this clipping is getting introduced. As for using clipping intentionally to imitate a very loud real life effect, I don't think it works well unless it's done very skillfully. The thing is, digital clipping sounds nothing like ear clipping, which involves both mechanical and psychoacoustic mechanisms. In any case, most of the really loud sounds in real life like jets and rockets are dominated by lower frequency energy, enough that you'll be feeling intense pounding in your body before your ears start distorting significantly. I'm rather glad movie sound effects aren't as loud as their real life counter parts, but in the interest of realism, I believe getting the bass right goes a long way. I think the Hell Carrier engines were done well in this respect. The real life event would likely be loud enough to damage internal organs, but we can suspend our disbelief very well when we hear the same sound as we would from a safe distance. In the Space Shuttle launch recording I posted, I believe SPL peaked well above 120 dB with the highest energy in the low 20s Hz and the bulk of the energy lying below that. There is no ear clipping at all, just a lot of pounding bass.

I will happily provide my subjective opinion once I have the chance to view this film. Too bad it already looks like another let-down on the audio front. Haha, I just remembered that I heard some pretty gross clipping on my system in the trailer. I had just assumed that was done to make it sound cool on an iPod, but I guess it was a true preview to the nature of sound on this film. Now that I think about it, I remember getting a huge grin when watching the trailer for Pompei. Of course, it was obvious even then that it was going to be a terrible movie. Perhaps previews have some usefulness after all. (As an aside, we need a web page that details precisely how many bass sweeps are to be found in various movie trailers.) It's always possible that the clipping heard was introduced intentionally. However, usually such clipping gets processed to soften it and enhance certain aspects of it, and the effect itself gets mixed in at a reasonable level. On the other hand, if the mix itself pushes beyond digital full-scale or another hard limit near digital full-scale, then the clipping will be very harsh. Not only is there no filtering to remove some of the high frequency energy, but also the level of the sound level of the sound and its clipping is also very high. How bad it sounds depends upon how much of the signal is exceeding the limit. If the excursions are isolated and associated with strong transients in the program material such as gun shots, then they may go unnoticed. When the clipping occurs with program material that is continuous but has strong micro-dynamics (i.e. high dynamic variation over short time scales) such as dialog, then one will likely here the clipping as a rapid succession of clicks. The density of the clicks and severity of of distortion depends on how many peaks are pushing over the limit. An actor yelling passionately may clip rather severely for the strongest syllable but still reveal a few clicks here and there on the parts of speech that are more emphasized. If continuous program material with low dynamic variation is mixed into clipping, then a lot more of the signal will be pushed beyond the limits, and the sound will be very harsh. This kind of sound can also fry tweeters quite readily if played back at high enough level for long enough. I've seen arguments put forth that the clipping resulting from peaks limited to 20% *above* digital full-scale is inaudible, a statement I strongly disagree with. In reality, this depends entirely on the program material, and crucially, the fidelity of the playback system. In the idiotic quest to make things as loud as possible, it's not unheard of to purposely mix things a bit hotter than 100% full scale. The loudness increases not just because of the increased sound level but also because of the psychoacoustic effect of harmonics contained in the "inaudible" clipping. In reality, such clipping is only inaudible to the extent that it may be perceived as an increase in loudness instead of as clipping. That said, a high fidelity playback system may more readily reveal its true nature. I have not yet watched WOTW, but a fog horn would probably have little micro-dynamic variation. If this sound is mixed even slightly too hot, it's enough to cause clipping that's likely very audible. The relative purity of the tone in the sound effect likely also makes it easier to hear the clipping. Note that bass often continuous, strong, relatively narrow band effects with little micro dynamic variation, so the clipping introduced by bass mixed too hot is very likely to be audible. From your descriptions, I'm quite confident that you are identifying clipping. That's not to say that every instance of clicking or harsh sound is due by clipping. For example, pushing a fader down too fast can introduce clicking that's not really clipping but is still unpleasant to hear. As already mentioned, many harsh sounds may be made to sound harsh on purpose. I don't completely object to this practice within reasonable limits, I mean artistic license is important, right? The thing is, the processing that is used to make sounds seem louder is not much like any process in nature. To someone with a less capable system, perhaps it might suggest to the listener that "something big is happening", since he/she is used to hearing distortion whenever "big things are happening", but the sound will be far from realistic. On the other hand, if the sound is skillfully recorded and retains both strong dynamics (though not necessarily as high as in real life) and full-range bass capture, then on a capable reproduction system, it will sound quite natural, literally surprisingly so in fact. What I am very curious about is if this clipping is mostly introduced in the theatrical production process, or if it's mostly introduced during the home release mastering process. I wonder how much the loudness war practices of popular music really do influence film. I also wonder if loudness is intentionally introduced into at least some home releases. The reasoning might go something like this: most users play at home at reduced levels, say reference -20, but the director wants to make sure that the home viewer gets "the same experience" that he/she would get in the theater. So the mixer sets about to create a soundtrack that sounds as loud at -20 as the one in the theater. This is probably a bit extreme, not that people don't listen at -20 or even lower, but that anyone would attempt to create a film mix "referenced" to playback at -20. I have heard previews that sounded like they used a -20 reference. They sound pretty bad too. The funny thing about dynamics on soundtracks is that the more heavily produced stuff (like big budget film releases) often sounds a lot less natural and dynamic; whereas, low budget work often has great dynamics. It seems often that the more minimalistic the production, the better it sounds. For example, the intro to "Beasts of the Southern Wild" depicts fireworks that, while not being especially loud, leave an impression. They sound a lot more like the real thing than any simulated example. I have come to enjoy the Danley recordings (fireworks, Harley motorcycle, parade, etc.) I think the Danley fireworks recording may be one of the best "slam" demos in my room. It's unbelievable how close to reality it sounds (and feels). I like movie soundtracks that give me that impression, even though they are few and far between.

The answer is: it depends. If all tracks came from the same master, then the only differences will be due to the encoding itself, in which case, PCM should be identical to DTS-HD or Dolby TrueHD, and these should be superior (if only subtly so) than the Dolby Digital encode. I have heard it stated that DD mixes have infrasonic bass rolled off, but I've never seen this claim verified. Note that when comparing the mixes subjectively, don't be fooled by different levels arising from use of Dialnorm in one of the tracks, usually the DD one. If used correctly, Dialnorm will lower the playback level of the track so that it its plays at a level consistent with other properly Dialnormed tracks. In order to make the comparison fair, the non-Dialnormed track should be level matched against the one that is DIalnormed. There may however be Blu-rays in which different tracks come from different masters. One obvious case of this would be a 5.1 DD mix accompanying a 7.1 mix in a lossless format. There may be other cases, such as a theatrical master in DD format being bundled along with a lossless near-field master. Unfortunately, when the tracks come from different masters, it's becomes harder to judge which track is better. For example, if the near-field mix was done particularly badly, then it is at least possible that the DD track might sound superior to the lossless one. How often this occurs in practice is unclear. It may be fairly rare, so that in most instances, it's still almost always better to choose the lossless track if it's available.

So I had to edit my post again about "The Fifth Element" and "OZ The Great and Powerful". It turns out that *neither* film advertises a copy of the theatrical mix. I'm not sure how I got this wrong in my memory for Oz. In the case of The Fifth Element, both a PCM and True HD mix are included. I probably ascertained that the PCM mix was a theatrical mix by how bright it sounded without an X-curve applied. Nevertheless, the True HD mix sounds just as bright. The levels also appear to be similar if not identical. It's close enough that I wouldn't argue for any difference without looking at the data to confirm. So having established that neither disc necessarily contains a theatrical mix, I have nothing to compare at this point. Is anyone aware of any Blu-ray discs that do explicitly advertise inclusion of the theatrical mix? I know I've seen (either here or elsewhere) speculative discussion that the DD 5.1 mix on Prometheus is a theatrical mix, based on the subjectively substantial difference between it and the lossless mix, with many commenting that the DD 5.1 mix sounds better and has more bass. Of course, I read reviews of "The Fifth Element" that claimed either the PCM or True HD mix to be superior when in fact they may be identical. All this makes make more eager to get at the audio data on the discs to do some loudness measurements. If/when I get around to doing this, I'll gladly share my methods and results.

As I described in another recent post, I would probably use something similar or even identical to the LKFS approach outlined in the ASTC paper to do loudness measurements. I'm not exactly sure how to answer your question about how to qualitatively identify clipping. Are you looking for a way to identify it by listening, by visually inspecting the wave form, or by using some kind of analytical technique? I can describe what I think clipping sounds like, but I'm not sure if that's the answer you're looking for. I pointed out the clipping I thought I heard on a single syllable of dialog in "Prince of Persia" because it stood out. Many films including almost all made more than a decade or so ago are riddled with clipping throughout the dialog. The human voice is very dynamic and difficult to record. For various reasons, this clipping tends to be fairly mild, and since it is so common in recorded voice, we don't tend to notice it much if at all. But with "Prince of Persia" that one little pop stood out like a sore thumb because the rest of the dialog was so crystal clear. Granted, I cannot 100% rule out the possibility that my equipment introduced the clipping. I seriously doubt it, but at the time, I did not do the "playback at lower level" test that I often do to make sure it's not my system. Thus far, each time I've suspected my system of having introduced the clipping, I've either disproved this suspicion confirming I still hear it in low level playback or found confirmation in this forum that the clipping is in the soundtrack. My amp also is supposed to illuminate red LEDs when it clips, and it has yet to do so, although I know little of the specifics of how its clip detection mechanism works. Realizing that clipping is fairly common in Blu-ray soundtracks, I've all but stopped worrying about what my system is doing.