Originally Posted by counsil
This is great information. Thanks. I will keep this for further reference.
How would it change if you had some of the bass re-directed from your satellites to the sub? Let's say with an 80Hz crossover on all of them.
Looking back 10 years ago to the Cirrus Logic, Inc. patent application for digital Bass management:
Dolby Configuration 1:
Left Surround (HPF)
Right Surround (HPF)
Bass: LFE+10dB, L, R, C, S summed to SUB.
NOTE: In cases such as Dolby Configuration 1, a gain of +10dB is not directly applied to the LFE channel to drive the subwoofer. Instead, the inputs to summer 802 are attenuated to achieve the same result. In this example, the L,R,C,Ls and Rs are attenuated by -15dB and the LFE channel is attenuated by -5dB. This implements the LFE + 10dB specified for Dolby Configuration 1. However, a compensating 15dB gain should be applied later, usually in analog, after the DACs.
This explains why early implementations of digital bass management had problems with low subwoofer output when switching from DD to DVD-A, or when using the player to decode and send the analog signals to the receiver, for example.
It's important to note that the low end of the satellites is summed with the LFE+10dB and then called 'Subwoofer'. This does not mean that a sound effect source that's encoded at 0dBFS in all 6 channels requires the subwoofer to produce a 116.8dB peak. It's means that the subwoofer is required to produce its part of the effect, combined with the satellites required parts to produce a total Sound Pressure Level of 116.8dB.So, is it possible to send 6 channels to an AC-3 encoder?
One of the biggest reasons is that DVDs (being primarily for video) are often mastered in the theatrical tradition, in a Dolby calibrated room. With full-scale levels, at the dynamically highest point, the audience would be deafened. Even more to the point, if you send 6 full-scale tracks to an AC3 encoder, the encoder will override the settings and slam the tracks with compression. I've had clients send me AC3 files that actually *muted*; I assumed for the same reason that a CD will mute a D/A if the decoder encounters too many overs.
This is a point I've tried to make many times regarding the requirement for reference level playback at single digits. There is no way an effect can have single digit content encoded at 0dBFS because there would be no headroom left for any other frequencies that comprise the total sound effect.
Contrary to popular belief, the levels encoded are watched extremely closely by the top people in the field.
I am impressed by the correct information given. However, there is one other factor. Dialnorm, built into AC-3 by the requirements of ATSC normalizes dialogue. Almost all Hollywood movies are made such that the average level of A weighted dialogue will be -27 dB re Full Scale. Dialnorm pushes this down by 4 dB, "normalizing" all dialogue to -31 dBFSrms. So small rooms calibrated to 85 dB SPL and playing DVDs from a Dolby decoder (does not apply to DTS) will play at 81 dB equivalent.
When you find your levels are lower than this, I'm afraid I don't understand why if you have calibrated as suggested. My students all mix dialogue within ±2 dB of each other on the Spielberg Scoring Stage in the control room at USC, which is calibrated to 81 dB. We find this interchanges with a much larger theater calibrated at 85 because everyone who has done it has found that the same SPL in a larger room sounds less loud than in a small one.
Hope this helps.
I have done hundreds of DVD feature remastering with a THX rep watching my meters!!! I can tell you their limit is max peaks at -6dBFS, momentary peaks during explosions etc not to exceed -4.
Here, same rules apply as with the theatrical mix, except that the monitoring is different (near-field, no X-curve), the room is smaller, it is calibrated lower, AND there is the dialnorm parameter if your sound is AC3 encoded.
You have to determine your target dialnorm BEFORE you start mixing, so you can adjust your listening level accordingly. Most DVD's are mixed for dialnorm -27dB (because that setting is the most compatible with the theatrical mix), but some use the full dynamic range (-31dB).
So, when remastering a theatrical release for DVD, you can employ a trick or 2 (LOTR/FOTR employed the dialnorm -31dB trick mentioned above for the DVD), and you can cut everything else and put all of your headroom into a more narrow-BW effect, like SW:AOTC chrome ship flyby, but I don't believe it's possible to send 0dBFS from all 6 channels to the encoder when working in DD AC-3.
I suspect that DTS and the new hi-def formats may be different, but I just don't know.
Getting back to SPL peak reading at home, again, as Seaton points out, there are examples of in-room frequency responses with room-induced peaks 4, 6, 8, 10dB or more at certain frequencies. If an effect happens to be centered at that peak in in-room response, the total SPL reading will reflect that.
Conversely, if you have a 10dB dip in response and a particular effect is centered there, you may be scratching your head as to how people report a 118dB peak during that scene and you are reading 105dB.
Sorry for the long reply. Just throwing out some trivia from my vaults.