Audio Post Details
Reflections. It's all about reflections, and it gets really messy in small rooms. Low frequency standing waves also wreak havoc in small rooms, which must be dealt with (or at least understood) if accurate monitoring (even in stereo) is to be achieved. But with 5.1 the complexity is amplified by the addition of 3 more loudspeakers and a sub-woofer. Placement within the space becomes critical (and I honestly didn't know just how critical until this exercise), as is control of reflections and standing waves. I researched and settled on a 5.1 monitoring system from JBL that fit my needs perfectly. Once installed, I still knew I was not ready to start mixing. Long story short, weeks later of measurement microphones, SPL meter measurements, standard test tones, measurements of the room using Room EQ Wizard (a very cool app), moving my sub around the room, sometimes by as little as 6 inches or so, and completely rearranging my space, I arrived at a room configuration that would provide me the best possible monitoring environment for surround sound mixing I was going to get..
The results were astounding. However, as with even the best calibrated dub stages used on the highest budget features, these stunning results only occur within a relatively small sweet spot (this is actually true in theaters as well). In my room, this sweet spot is basically where my head is when I sit in my chair with back straight exactly 48" from every monitor. I used the ITU recommended configuration where the Left and Right speakers are 30 deg off axis from Center, and the Left Surround and Right Surround are between 110 and 120 deg off Center on either side, all placed on a circle (in my case, with a radius of 48 inches). Sub-woofer. placement was dictated by the room and its nodal structure, as it is non-directional.
The ultimate goal of such room calibration is to conform to the same SMPTE standards agreed to and used by theaters worldwide, which will then (do much to) ensure that what you produce in that room will translate accurately to a calibrated theater. Part of this is level calibration, which is done by sending a standardized pink noise signal which provides a -20 dBFS signal level to each monitor in turn, the volume control of which is then adjusted to provide 85 dB C-weighted, slow response (dBCs) on a sound pressure level meter at the listening position (SMPTE standards dictate that the surrounds are adjusted 3 dB down to 82 dBCs for cinema). This same procedure is used in dub stages and theaters all over the world during calibration, so that everyone is working to the same standard.
This worked great until the loudness wars that plagued music on radio bled over into movies and overly loud trailers and films prompted complaints from patrons and resulted in movie theaters turning down their master faders to non-standard levels. This caused complaints about properly mixed movies being played too soft, where dialog became inaudible. Quite the mess that is the source of much lamenting on Gearspace and other post-production forums frequented by sound professionals worldwide (it's unsurprising then that all three of the theaters I tested my Dead Run DCP in had their faders turned down below the SMPTE standard settings for a properly mixed soundtrack. As a result, my soundtrack was quieter than designed and what I heard in my room).
Typical dialog in a theater sits at about 60 dB, and peak sound levels I've recorded at movies have reached up to 100 to 110 dB, for a 40-50 dB Dynamic Range, which is much higher than any music you'll hear today. That's what gives movie soundtracks such appeal, emotion, and excitement. As filmmakers, we can only ensure the mix is right when it leaves our hands, and hope theaters maintain their calibrated systems. Another difficulty for indie filmmakers on the festival circuit, is while some require DCPs to maximize customer experience, others can only play digital files from a laptop connected to a consumer projector; not the way you'd like your hard work to be seen (or heard). DCI standards for DCP dictate that DCPs cannot be stereo (2.0), but must be either mono or 3.0 and up. However, most festivals that don't accept DCP still play a digital file in stereo, which is never ideal for theaters due to problems with phantom centers and people sitting closer to one speaker than the other, causing diegetic sounds to be disconnected from the image. But if you want a wider, more interesting sound-field, it probably beats mono. Dolby ATMOS, ambisonics, and similar technologies can also turn a pair of headphones into quite an immersive listening environments as well.
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