Nest Music Theater Part Twenty Nine ~ Derived & Discrete 5.1 Soundfield 05Feb24 - Updated/Resolved 06Mar24

Signaling & Driving  Surrounds... My Dolby DP564 suffers a failed left surround analog out so I needed to find a work around which gets me both surrounds. I did not prefer the large Denon AVR used during the NOnken surround "experiment;" I gave that to Matt anyway. I want to get the surround signals from the DP564 as it works well for the center channel already. The digital outputs of the pro DPS564 are AES3IDs with BNC connectors and carry 2 digital channels on each. So, LS & RS, are 2 channels mixed together on one AES3ID digital out. I found the Radio Design Labs HR-UDC1 converter from Prescott, AZ which accepts pro digital AES3ID and converts that to consumer SPDIF optical & COAX. Good start in a half rack form factor for this esoteric piece, though it was pretty darn expensive for what it is.

I also therefore needed a 2 channel dac/amp to take the LS/RS on SPDIF from the converter and render and drive those channels out to the surround speakers. I've had good experiences with Topping previously and selected their MX3s DAC/AMP for the task; it's a 24bit/192 KHz DAC with a 30W/chan D-amp with low distortion and full remote control. Excellent... I tested it first in measurements (as seen in the surround speaker Tri-Port building post) and it is basically equivalent to my NAD DAC/AMP. I'm running standard stereo signals on coax to the surrounds and derived or discrete surround signals on optical to the surrounds.

Derived Surround Impressions... all the pieces do their jobs well and the new surround speakers sound good rendering the Dolby PLIIx LS/RS as well as straight stereo. As noted prior in this blog, the PLIIx surround signals derived from 2 chan PCM are necessarily pretty thin. The surrounds add to the music theater experience but not as significantly as some full blown DSP efforts included in many older AVRs. I can't vary the surround sound as much as one can with those AVRs but PLIIx is one of the better, if subtler, derivations any way. I am satisfied with the expansion of the NestMT to derived 5.1 for music; it even sounds great piping stereo to the right & left surrounds. I still have the challenge to get true discrete DD 5.1 out to the center and surrounds from the my streamer however.

Discrete 5.1 Signaling... Enter digital audio extraction again. I use the OREI 102A, a 48Gbps 8K/HDR HDMI 1:2 splitter/extractor, to extract audio from HDMI out onto SPDIF optical. The HDMI audio & video are replicated to the Sony TV without loss and the audio extraction is sent to the DP564 through the Felston delay device. The DP564 "knows" what it's receiving and outputs center and surround channels appropriately from inbound DD 5.1 or derived from 2 ch PCM.

I did have to resync the center & surrounds to the mains after adding the OREI into the audio path. I used an impulse response at the listening position to measure the delay incurred in the L&R mains from processing used in its audio path vs direct extraction from HDMI by the OREI for the CC & LS/RS. It was a whopping 158msec... once I added that via the Felston box (for Roku streams) all was glorious.

Roku Ultra vs Apple TV 4K... I could not get the Roku Ultra (Model 4760X) to pass discrete digital even when source material was in that format natively. The DP564 would not sync to the DD stream. An updated model of the Roku Ultra might do it but I supposedly confirmed via a dive on forums that an Apple TV 4K will transcode whatever discrete multi-channel digital content is playing to DD 5.1, as I desire. I bought one. It exhibited the same behavior when streaming DD 5.1 to the DP564. I've concluded that it must be the age of the Dolby box and its inability to fully recognize (it does see DD) and sync to the stream for discrete 5.1 content. Despite the setback, I am in the mountains and caught a keen scene of new-fallen snow from the deck of the Nest.

So, I am stuck with derived PLIIx CC and LS/RS for now, which is pretty darn good for most of my listening.  I switched back to the Roku Ultra (it wasn't root cause) and have even removed the splitter/extractor... it isn't really needed except in attempts to get discrete 6 channel sound (I readjusted delays). The surrounds can be driven not only with derived PLIIx signals but I can also send them straight stereo. Sure this is kind of a hairy setup but by using this configuration I can match the best decoding and amp for each channel, rather than being stuck with just an integrated AVR. Here's the current connection diagram.

Updated 06Mar24 ~ All Issues Resolved... I am no longer stuck with simply derived Dolby surrounds when content has DD+ or alternative discrete multichannel content! It has been a long road to configure a solution which delivers 2 channel PCM from Roku to the main L/R infrastructure, while delivering derived or discrete signals to the CC and the LS/RS. I decommissioned the Dolby DP564, RDL HRC-UDC1, and the Topping MX3s. The later two devices work fine but are no longer needed. The biggest issue has been the old Dolby box and trying to get it to understand new Dolby signalling ~ that was futile. I found and installed an oldish Yamaha AVR, TSR7810, which could handle UHD/HDR/DD+ on HDMI and had pre-amp outputs for every channel in (up to) a 7.2 setup. This latter feature is vital as I have the amps for mains and CC, and even the main L/R decoding I want, but I needed stable, modern surround decoding. The new config delivers UHD/HDR to the monitor and DD+/6 channel PCM/2 channel PCM or whatever is best for the original content signal, for center and surrounds through the AVR while maintaining a solid 2 channel PCM to the miniDSP for the mains. Woohoo. One vital piece was setting the OREI extractor's EDID to force the optical digital audio extraction to 2 channel PCM for the mains. Here's the final connection diagram and the new Yamaha. It all works great now but I still need to get some longer HDMI 48Gbps cables to button it all down, complete programming of my universal remote, and remeasure and reset delays. I guess too that I should sell the decommissioned gear.

I remeasured, set delays (using the AVR's lipsync feature to the measured 189msec, most of it processing time), updated the universal remote, and buttoned everything up. The Nest Music Theater is now fully 5.1 capable, including playing incredible modern movies' soundtracks. I don't have Atmos presence speakers above the front or back... hmmm.