Digital Extreme Definition (DXD)

  • UltraKops


    ACA Member

    The world's first ultra hi-resolution DXD download site, Promates Music Store, has launched from Copenhagen. The brainchild of Peter Scheelke, who in 2003 helped found Digital Audio Denmark (DAD), creator of the world's first commercial DXD converter, the site currently offers 26 native DXD recordings (352.8kHz sampling rate and 24-bit bit depth) from labels Dacapo and OUR Recordings.

    "We have to make people aware of DXD," Scheelke told Stereophile via Skype. "I'm starting off with enough material for people to test. Once people are aware of the format and the store, I'll go to the labels and request more material. I know they have the converter to record directly to DXD, because I created it."

    According to Scheelke, the reason it has taken until now to launch a DXD music store has to do with file size. While the size of a typical DSD album file is approximately 1.5GB, a DXD album often exceeds 5GB. Thankfully, faster download speeds and large storage have now made DXD downloads practical.

    "The sound is softer and warmer than DSD," he asserts. "It's far more calm and analog-like."

    Scheelke explains that the DXD format arose from the need to make an editing system for DSD that would have minimal impact on sound quality. Scheelke offered to build a converter for Merging Technologies, whose Pyramix system is used to edit and assemble DSD masters, that would record directly to DXD. From this arose Merging Technologies' Sphynx 2, an A/D converter that DAD built for them in 2004 as an OEM product. Also released by DAD under the name AX24, the unit was capable of creating digital files in DXD, 384kHz, DSD, and DSD128 (double DSD) formats, as well as PCM from 44.1kHz to 192kHz.

    "The problem is that if you are doing a recording in DSD (1-bit, 2.8224MHz sampling rate), you cannot edit in DSD, because you cannot edit a 1-bit stream," Scheelke says. "So you need to convert to DXD, and then convert back. Each time you do so, you add a new amount of noise.

    "DSD has a major problem with out-of-band noise. Without a noise shaper, DSD noise is around 85dB in the whole frequency range. Each time you convert DSD to DXD and then back again, the noise will raise and raise and raise. Eventually, because of the noise, DSD will no longer comply with the Scarlet Book definition of DSD. This is why someone like Michael Bishop does his mastering while he's recording. It's one take, and that's it. This strategy eliminates the extra out-of-band noise."

    To back up his statements, Scheelke has posted a long paper on ProMates that discusses the store's audio formats and their characteristics. To underscore the superiority of DXD, he also includes three graphs that detail what occurs in A/D conversion. The paper concludes with the following statement:

    For me, it is clear that there is an undeniable relationship between resolution and quality. Each format seems to have has its own expression and conversely, its own limitations. To reproduce classical music, for example, I have always preferred the quality of DSD.

    Yet, it was not until I experienced DXD that I was no longer able to hear the signal as a digital reproduction. In contrast, DXD is calm and warm, with a deep, resonant and well defined stereo perspective. So much so that it evokes memories of the heady days of analog.

    The Promates Music Store contains two different recordings of symphonies by Carl Nielsen. Both are performed by the New York Philharmonic under Alan Gilbert, and recorded in the same hall using the same microphones. The major difference is that while the file of Symphonies 2 and 3, which was issued as an SACD, was recorded in 88.2kHz due to a customs snafu that slowed the import of DXD equipment into the US, the subsequent recording of Symphonies 1 and 4 was done directly to DXD. Perhaps microphone placement was a bit different on the second go-around due to increased familiarity with the hall, but that and the digital format are the only difference.

    Scheelke encourages audiophiles to download both recordings and compare the sound. Although my ability to do so was limited to desktop and headphone listening, the Audeze LCD-2 headphones, abetted by Nordost Heimdall 2 headphone cabling and connected to an Antelope Zodiac Gold DAC, clearly conveyed the greater atmosphere and depth of the DXD recording.

    "When you compare DSD to DXD, the DSD is quite good," he says in conclusion. "If you do all your recording in DSD, and only convert to DXD once for mixing and editing, it will sound quite good on most equipment, depending on the limits of the amplifier and converters. But I've been in most of the best studios and listened and listened, and if you have a DSD file that you edit in DXD and then convert back to DSD, and you compare it to the original file, you can hear what you've lost. For that reason alone, since DXD is the format you are using when you create an SACD from DSD files, then it more than justifies listening to DXD by itself.

    "The only reason to use DSD is that you get a smaller file, because DXD is better. No disc can hold a DXD album. This is why no one knows about it, because it has to be downloaded. Most of the guys who produce SACDs do so from DXD files. I know this for a fact, because I probably sold them the converter they are using. There are thousands of recordings in DXD out there—probably half the SACDs out there were recorded in DXD on a Pyramix system—but no one has heard them in the DXD format."

    Peter Scheelke is out to change that. As far as he is concerned, DXD's tim

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    1  11 Dec 2014  
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