SME Posted December 19, 2017 Report Share Posted December 19, 2017 This thread is more about full-range content than bass, but it is content related, so I think it works best here. In the future, I may post this somewhere on AVSForum, but for now I want to keep it to a limited audience. As I've mentioned in the main LF Content thread, the X-curve calibration standard in cinema causes two major problems: Tonal balance that deviates substantially from neutral and from what is typical used (informally) for music production and what sounds good on a home system that is optimized for music. Inconsistent calibration between different dub-stages and cinemas. As I also noted, many UHDBR/BD/DVD releases these days have high quality home remixes that fix most of these tonal balance problems. This is true for most recent Disney releases these days (including, e.g. the new "Star Wars" and much recent Pixar and Marvel stuff). However, much legacy content as well as lesser quality home-remixes do not feature any re-EQ and retain the inverse-X-curve signature. The effect of X-curve calibration is to attenuate both high frequencies, via the -3 dB/octave slope in power response, and the low frequencies, which arises from forcing a flat power-averaged response even though virtually all speakers have a significant drop in directivity for low frequencies and what absorption is present in typical dub-stage / cinema rooms is also less effective at low frequencies. As a consequence of the altered tonal-balance, most mixes are likely altered to sound good in the dub-stage during the re-recording mix process in which highs and lows are boosted to compensate. The resulting mixes, in addition to translating unreliably between theaters, sound less than optimal when played back on a home system. The auditory symptoms are mixed. I find it easiest to hear the problems in the dialog. Sometimes only one of the excess highs or the excess lows is audible in the unaltered track because the boost dominates. For example, some cinema mixes, the dialog comes across very bright. In others, it comes across very boomy. Sometimes, the dialog seems relatively balance, in terms of high vs. low, but with the mid-range being relatively depressed, intelligibility often still suffers. Dialog is both much easier to understand and much more enjoyable to listen to when it's presented neutrally. Unfortunately, the required correction varies between track for both of the above reasons. Mixers don't necessarily attempt to defeat the X-curve alterations in any systematic way. Instead, they "turn various knobs" and listen until they are satisfied with the result. So the ideal filters to reverse their changes may vary between mixes. And because the X-curve calibration method isn't even consistent between dub-stages, EQ-adjustments that give good sound in one dub-stage may not work well in another. In fact, there's evidence that X-curve calibration doesn't even achieve consistency between the left and right vs. center screen channels vs. surround channels in the same dub-stage. The situation is a big stinking mess for sure. Nevertheless, even if the adverse effects of the X-curve standard on the mix cannot be perfectly reversed, it's possible with some rudimentary EQ to improve the sound quality of cinema mixes considerably. Now that I've finally achieved a stable, reliable audio reference in my own sound system, I've been giving attention to this problem. In this thread, I hope to document some of the candidate corrections that I've applied to improve the sound quality of various movies. I would encourage anyone with the required capabilities to give these a try and share feedback. To implement these requires the ability to apply various biquad EQ filters such as high and low shelves and Peaking EQs, ideally to the streams *before* bass-management. Though for my first pass, I'm applying the filters identically to all channels, so it should work fine to apply them after bass-management as well. One issue I imagine most people will have is that they have a limited number of free filter slots. The more filters used, the better quality correction that's possible. I will try to limit the filters to what's actually needed. Edit: I posted a candidate correction for "Wonder Woman". Sweet! Edit2: TL;DR: I don't recommend using any "corrections" that I posted here. This was mostly a failed experiment because most tracks don't exhibit a predictable inverse X-curve signature. Instead it would seem that typical EQ adjustments are typically smaller and less stereotypical. Furthermore, EQ problems seem to be inconsistent within different parts of the same track (not just by channel), which means improvements to some aspects of the track are likely to come at the cost of degrading other aspects. I also discovered that it was extremely difficult to get the shape right in the upper mid range, with nasty resonances resulting from errors. Even now with much more precise response optimization for my system, I'm skeptical that any improvement I get with EQ will reliably translate to other systems unless I somehow manage to neutralize the original errors very precisely. To do so would require more skill and better tools than I have. This isn't just *my* problem but seems to be an issue with many of the home releases that do sound they like were re-EQed (e.g. many recent Disney). I very often hear upper-mid resonance issues (albeit mild) on these titles, and I rarely hear such issues with mastered music. 2 Quote Link to comment Share on other sites More sharing options...
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