Q I own an NAD T 787 A/V receiver that only supports regular HD video pass-through and Dolby True HD/DTS-HD Master Audio processing. This receiver features NAD’s MDC (Modular Design Construction) for hardware upgrades, and I’m looking to add a new HDMI module so I can pass-through 4K video with Dolby Vision HDR. NAD also offers an audio module with Dolby Atmos support, along with outputs for two sets of height speakers (using an extra amplifier). I’m not sure if adding height speakers will work in my room, so if I stick with my current 5.1 speaker setup, would the Atmos upgrade improve sound quality? Or will my receiver simply downmix the Atmos soundtracks to 5.1/7.1 surround with no audible improvement? —Phil Tomaskovic, via email
A While Dolby Atmos and other object-based formats do represent an upgrade over “channel-based” Dolby TrueHD and DTS-HD MA surround, Atmos in home systems is actually delivered using either the standard Dolby TrueHD (Blu-ray and Ultra HD Blu-ray discs) or Dolby Digital Plus (streaming services and broadcast TV) codecs. To provide backward compatibility with non-Atmos processors, the “height” information exists as an extension to the core 5.1- or 7.1-channel soundtrack bitstream. An Atmos processor in an A/V receiver or soundbar will “see” this information and decode it, while non-Atmos gear will ignore it and process only the core soundtrack.
Now that we’ve dissected Atmos, how does that information apply to your NAD T 787? Unless you plan to eventually add height speakers to the system, there’s no real benefit to buying the Atmos module. Dolby TrueHD delivers lossless audio at 24-bit 96kHz resolution, while Dolby Digital Plus compresses audio and delivers it at a lower bitrate that’s optimized for streaming (though the compression level used for DD+ is less aggressive than that used for standard Dolby Digital). And since your AVR is compatible with Dolby TrueHD, you’re currently getting the best possible surround audio quality, though the sound does lack the height dimension that Atmos adds.
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