Sound Calibration questions

[Marco Giustini]

I've heard some discussion that many auditoriums do not have sufficient LFE even though they look good on an RTA. This is due to the reflections adding to the direct sound and giving a higher RTA reading while it is desired to have the frequency response be determined based on direct sound, without the reflections.

Yes, this matches my experience. Some rooms would sound perfectly fine with the RTA level, some other will just lack LFE.

As it's been said, a proper calibration must involve the playback of known content and adjustments might be needed. Usually good acoustic = less or no adjustments.

That said, Ron, I wouldn't worry too much about that just yet. My advise is to learn how to properly calibrate the room with the tools you have. Learn how to use the sound processor etc.
Experience will come.

Thanks for the link, Harold, that's a long and interesting one!

[Jay Wyatt]

SMPTE currently has several groups working on cinema sound, especially finding a way to measure the quality of the sound such that a number corresponds with the perceived quality (people and the measurements agree on which one sounds better). A danger in the use of perceived quality is that the listener may prefer a sound that is different from what the content producer preferred. Ideally, we hear what the producer produced.
Harold

Kind of but not quite Harold. 27C is exploring in-situ measurement methods and looking for trends in all types of rooms (budget, standard cinemas, high-end studios). When there's a high correlation between metrics that are measurable (objective) and perceptional scores (subjective) then they may be able to say with some confidence certain criteria may be important. There is some risk I suppose in scoring perception but this is being done by committee of trained listeners on content all are extremely familiar with. When the links are found and a measurement procedure gets defined then the perceptual "score" becomes less important and that danger goes away.

Hopefully this could shed light on why two systems may measure the same on an RTA but sound completely different with program -- the LFE riddle mentioned in this thread for example. This doesn't override the existing tuning practices and targets in place (ST202 & RP2096) where both measurement and listening are important. I see it as creating a system qualification check to be carried out before calibration steps are taken -- do I have enough LFE subwoofers, do my amps have sufficient headroom, can the loudspeakers reach peaks without distortion etc... Determine first that the the gear in the system capable of doing its job and reproducing the the mix, at reference level, in a linear fashion.

[Harold Hallikainen]

Thanks for the comment! Great to hear from you, Jay. My comment on listener desire versus sound accuracy (does it sound like it did on the dub stage where it was mixed) is based on a study several years ago that said the X curve was incorrect. A group of listeners were given some sort of equalization control (or tone controls) and adjusted the equalization for the best sound. There was, as far as I know, no attempt to have the sound match that (as closely as possible) on the dub stage. Different people like different sound, but, I believe, the goal here is to match, as closely as possible, that of the dub stage where the content was produced. I am hoping that multitone spectral contamination tests will correlate with the perceived quality (as compared with the dub stage), but we will see how the SMPTE tests turn out.

Again, it's great to hear from you Jay! I really enjoyed working with you at USL.

Harold

[Marco Giustini]

Yes, there is a risk of "making things worse" when listening to content - if one is not experienced, trusting the RTA would probably be the right thing. I use the same content over and over again, some of it I had a change to hear in a dubbing stage while the final mix was done. I don't pretend to have "calibrated" ears but I might be able to spot something wildly off - which usually happens when the acoustic is also "wildly off" BTW.

So yes, let's not pass the idea that it's ok to just "do an EQ by ear" but I think it's important to agree that the target curve is a (good) starting point which then might need some tweaks not because of personal taste but because the RTA does not work like our ears and an experienced technician can improve on it.