The Dolby Atmos Music Target Curve. And on being an audiophile "tonmeister".

[For the post this week, let's take a pause from the Pacific Audio Fest 2024 discussions (last 2 weeks). Next week we'll have a Part III discussion about audio shows.]

Standardization is generally good.

I've discussed in previous posts that Dolby Atmos defines loudness characteristics for recordings and this has helped preserve dynamic range in multichannel/Atmos albums following their guidelines. Likewise, we can benefit from standardization of the frequency response as this will allow us to better "translate" the sound from the studio into our sound rooms. This idea is not new for audiophiles. The ill-fated (with good reason) MQA promised that we could experience the "sound of the studio", but they never could deliver in a large part because there was never any standardization for essential parameters like the frequency response, among other failings. In the same way, back in the day (~2014), this was the promise of hi-res audio by Neil Young and Pono that you would somehow get the "finest digital copy" and this would represent the sound the artists intended from the studio; clearly they overpromised and under-delivered by 2015.

It's one thing to standardize between the studio and home ("inter-system") playback, but it's also important to standardize "intra-system" - that is, between all the speakers in your set-up when you're doing multichannel such that each speaker is calibrated to the same timbre. This is important in a multichannel layout since we do not want "objects" moving through space changing tonality because of mismatch between speakers around the listener. The Dolby Atmos Music Target Curve is Dolby's recommendation for the music studio frequency response. This curve evolved from the X-Curve, an 'X'perimental frequency response based on some early empirical work exploring the performance of actual theater sound systems starting in the 1970's, and evolved over the years. See this paper for more details, note some similarity of the Dolby Atmos Music Target Curve to the SMPTE 202M - 1998 X-Curve.

As with all things in audio, nothing wrong with asking whether this curve is the "best". 🤔

Seating variations, multi-seat correction & multichannel DRC. The audio "sweet spot".

A look at the rear of my room and the sofa seating - surround speakers, LP rack for a little bit of diffusion room treatment. For best practice, it's important to not sit too close to the back wall. I have 3' between the couch and the LP rack, and the rack is about 17" deep before that back wall. 

Before putting the UMIK-1 microphone away after using Audiolense XO as discussed last time, I thought it would be interesting to explore in greater detail what happens with frequency response and time-domain performance as we sit off the "sweet spot" where the measurements were collected and correction calculated for.

In the image above, I've put a meter stick on my listening couch to identify the seating positions 1 and 2-feet to the right and left of that sweet spot so I can take detailed measurements of what happens to the sound coming from the 5 main speakers at those positions with and without DSP turned on.

Multichannel Digital Room Correction with Audiolense XO. And "What's your budget?".

As you might recall from over the years, I strongly believe that one of the most important things one should try as an audiophile seeking high-fidelity - after having a decent sound room, and getting good equipment - is to consider the use of room correction. It could be as simple as frequency-domain EQ correction for larger bumps and dips (as discussed with the Behringer DEQ2496 hardware back in 2013-2014, device measurements here), or the much more sophisticated frequency and time-alignment of filters created by software like AudioVero's Acourate (and 2019 update) capable of much higher resolutions.

The power that one has to optimize and customize the sound runs well beyond most hardware upgrades other than wholesale speaker replacements and changing sound room! The change one can expect with room correction dialed in is astronomical compared to all the snake oil tweaks, cables, hi-res DAC/streamers, even amplifiers you might want to throw at your system.

These days, I've increasingly been converting multichannel content over to my Roon server, typically 5.1 SACDs and DVD-As but also Bluray rips, ideally lossless TrueHD with 7.1 channels. Unfortunately, Roon is currently unable to decode codecs like EAC3-JOC (lossy multichannel/Atmos) or TrueHD (lossless, based on the MLP codec) so the content typically gets transcoded to multichannel FLAC-compressed PCM which can handle up to 7.1.  

Although Acourate can be used for multichannel filter creation, the manual procedure here is unfortunately quite involved and more than most audiophiles would like to get their hands dirty with! Which is why today's post is going to be about multichannel digital room correction using Juice HiFi's Audiolense XO (€390, currently version 6.21). I see that there is the less expensive Audiolense Surround which I suspect could be enough for many users, and if all you need is 2-channel stereo, there's Audiolense 2.0.