Morten Lindberg of Norwegian music label 2L.
On this page in Stereophile‘s December 2023 issue, contributing editor (and mastering engineer) Tom Fine and I described a press event at which Apple Corps (the Beatles umbrella corporation) presented the news about the (at the time) forthcoming new Beatles single and the forthcoming “remixed” reissues of the “Red” and “Blue” Beatles compilations. Tom attended the event—which, notably, was held at Dolby headquarters here in New York City, reflecting, apparently, Apple Corps’ interest in Dolby Atmos. At the event, demos were presented in the Atmos format only—no stereo.
A key point of that column was that Apple Corps, at least—and who knows how many others in the music industry—are abandoning high-quality Atmos in favor of that streamed by Apple Music. Tom and I criticized this development in no uncertain terms, concluding that if Apple’s lossy-compressed version of Dolby Atmos is what we’re being offered, “we should hope for its demise.”
Were we too harsh? I asked an expert.
Far and away the most common distribution method for Dolby Atmos music is streaming, mainly via Apple Music. That Dolby Atmos, though, is lossy-compressed, to 768kbps. Note that that’s the total bitrate and not the per-channel bitrate, and this form of Atmos supports up to 128 virtual channels. That’s in contrast to the version of Atmos typically provided in “deluxe” Blu-ray packages: the “TrueHD” form.
At the event, Tom asked Apple Corps CEO Jeff Jones whether Beatles music would be made available in a better immersive form, perhaps on a Blu-ray disc, as it had been on some earlier “remixed” Beatles albums. His response: The streaming version of Atmos “made the Blu-ray obsolete.” Why? Because that Blu-ray disc raises prices, and “very few consumers care.”
That’s probably true. Unfortunately, Stereophile‘s readers (and writers) are precisely those “very few consumers.”
How widely Jones’s opinion is shared in the industry is, of course, unknown. I fear that it is widespread, if only because we’ve seen (and heard) this before: The industry has long felt secure appealing to the undemanding center. The development of widespread lossless and hi-rez music streaming (in stereo) was a very welcome surprise.
As I write this, the December Stereophile hasn’t been out that long, but the opinion we expressed has already proved controversial. Some perceived it as a “get off my lawn”–type judgment on immersive audio generally, or even of multichannel music, which of course it was not. One prominent audio engineer, who has worked on a lot of hit records, said he thought we were wrong on the facts—that Apple’s Dolby Atmos is not in fact lossy (how could he not know that?), but that even if we were right, it didn’t matter, because the work of those wonderful recording engineers (including, presumably, the ones who don’t understand the format’s technical limitations) would render any lossiness moot.
It’s true that our argument had a vulnerability. Ultimately the proof is in the listening, and I’ve never heard Apple’s lossy Atmos on a really high-quality system. In stereo, 768kbps is an impressive bitrate; it would be difficult to differentiate from full CD-rez. Maybe—just maybe—it is good enough for Dolby Atmos, despite its being a profoundly multichannel format.
Morten Lindberg is the producer and recording engineer for Norwegian music label 2L. He has been nominated for 35 Grammy Awards and won one, in 2020, for Best Immersive Audio Album. Nominations continue to roll in.
2L is notable for its commitment to astonishing musical and technical standards. On the technical side, Lindberg records in 24/352.8, in 12 channels: 7.1.4 (footnote 1). That resolution is preserved throughout editing, mixing, and mastering. What happens after that depends on the distribution format—and 2L offers the widest selection of distribution formats of any label I’m aware of, all the way up to 12-channel 24/352.8.
Importantly, for my purposes, 2L offers Atmos downloads in two forms: the lossless “TrueHD” format Tom and I praised and what 2L calls “Dolby Atmos in MP4 file.”
Every recent 2L release, then, is available in both the highest-quality lossless Atmos and (as I confirmed) a lossy Atmos version identical to what Apple Music streams.
I asked how Dolby Atmos files are made. “I don’t mix for a codec,” Lindberg told me in an email interview. “I record for a playback environment. Any codec should then ideally provide for a transparent transport to the consumer. Our immersive workflow is totally independent of destination format.” “Our 7.1.4 channel-based master”—which as noted is 24/352.8—”is then mapped to eight bed channels, and the four height channels are defined as static objects. Creating the Dolby Atmos Master ADM (Audio Definition Model) is simply a matter of implementing the metadata and converting sample rate to 48kHz.” Though a factor of 7.35 smaller than the original source, “the resolution at this point is still uncompressed linear PCM, in discrete channels. The ADM is encoded to MLP (Meridian Lossless Packing) for Dolby Atmos in Dolby TrueHD as you find on our Pure Audio Blu-ray and in the MKV container.
“The ADM is our delivery format to the aggregators for the consumer services. Unfortunately, the services currently reduce the resolution by perceptual encoding compressing 10:1, very much like MP3. Tidal make two paths; for binaural on mobile devices for headphones they use AC4-IMS”—that’s a binaural codec, not multichannel, something I had misunderstood—”and for speaker environments they go with DD+JOC”—what’s commonly referred to as Dolby Digital Plus with Dolby Atmos. “Apple Music stays with the latter codec for both speakers and its special headphone virtualization.
“Our MP4 version of Atmos is identical to Apple Music’s version, at 768kbps. Our Dolby TrueHD bitrates average around 6000kbps with peak data rates up to a maximum of 18,000kbps for high sampling rate multichannel content.” For comparison, stereo 24/192 uncompressed has a bitrate of about 9000kbps, so that’s a lot of data.
What, then, is Lindberg’s judgment on the version of Atmos disseminated by Apple Music?
“The lossy version of Atmos is to me a bleak shadow of the real, uncompressed source.”
Footnote 1: For Atmos, the number after the second decimal is the number of “height channels.”
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