Why are cinema surround speakers set to -3Db?

[Turisu]

Is it to compensate for the fact that the front 3 speakers are behind the screen? And if so, is the intention that the audience perceives the levels as the same?

If this is true then the accepted wisdom that cinema DTS rips need to have their surround channels attenuated by -3Db for home viewing would be wrong.

It's interesting when looking at home mixes that are close to their theatrical counterparts as some apply the attenuation and some don't.

[zoidberg]

In the theatrical environment the surround speakers are set to an acoustic sum to match each front speaker, this corresponds to -3dB. In the home environment speakers are all set to the same level so the incoming surround level should be attenuated. If I'm wrong please correct me

[Turisu]

I guess the pertinent question is how does the audience perceive the sound in the theater? Do the surrounds actually sound quieter than the fronts? Because at home a -3Db drop is going to be quite noticeable.

[zoidberg]

Well the studio in which the audio is mixed is set to the same level so the audience hears what the mix engineers hear

[Turisu]

I guess that settles it then. Thanks for your insight.

[spoRv]

IIRC the surround channel(s) is(are) set -3dB to compensate the fact there are many speakers for each channel(s) instead one for each in the front, so to let each speaker sounds a bit lower - think about viewers very close to side or back speaker - while when heard all together the summed level lead to the right one.

At home (if I'm not mistaken) it *should* be set 3dB higher than theater becasue any channel has its own speaker - unless we are talking about Dolby Surround (the original)/Pro Logic or EX or DTS-ES when a single channel pilots two speakers...

About the wrong level on some Cinema DTS (and subsequently laserdisc, where DVD were corrected AFAIK) it was one of the two, I can't remember which though:

- at the beginning studios sent mixes with same levels set, hence subwoofer 3dB and LFE 10db hotter
- first APT-X100 decoded (at home) decoded levels in the wrong way, then new versions corrected it

[zoidberg]

It's 82db per channel, not per speaker. The left and right surround channels acoustically sum up to 85dB, it goes back to when surrounds were mono and carried over into the discrete age. Also room calibration almost invariably is based on an optimal listening position somewhere in the middle so viewers too far front/back/to either side will hear a less balanced mix.