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Reset. When AudioMidi wouldn't recognize the MA-1's USB input as selectable audio device—my equally XMOS-based Eximus DP1 and Stello U3 never suffered such rejection—Rashid explained that I needed an XMOS firmware reset. "Your DAC was shipped before final versions of the DSD-over-PCM firmwares were ready whilst the specification was still in flux. At this point the 1.0 spec is solid and the XMOS firmware is finalized but the system firmware will not be until next week."

Currently in Japanese only, this site purportedly offers 1200 DSD download titles


That was my cue to run in the MA-1 with my Audiophilleo 2 USB-to-S/PDIF converter above whilst reading up on the new spec. That turns out to be an open standard which allows the packing of DSD data inside PCM frames for native USB transfer without format conversion. Because OS X and Core Audio support PCM only (Windows leaves room for 'raw data' formats albeit sans specifics), the spec's desired compatibility with both operating systems meant a PCM path by default. The DSD signal would thus have to be accompanied by special flags or headers to differentiate it from regular PCM streams.


Those flags trigger the receiving hardware into detecting a format change and switch their decoders to Direct Stream Digital. The latter's 1-bit sample rate of 2.8224MHz is far higher than Redbook but its bit rate far lower. DSD's data density turns out to be equivalent to 16-bit PCM at 176.4kHz. By adopting a 24-bit/176.kHz transfer protocol, the new open standard adds extra bits for the required identifiers. Those mark a 'Trojan-horse' PCM stream as really containing DSD. Soft/hardware not configured for such files will simply read them as low-level noise. That indicates to the user a non-supported file format. With Channel D's Rob Robinson part of the effort and my iMac already on his latest PureMusic 1.86 software, I was assured instant support from my player of choice. This would properly tag DSD files in compliance with the new protocol. Supporting it at the time of writing were Aesthetix, Audirvana, Channel D, dCS, JRiver, Merging Technologies, Playback Designs, Sonic Solutions, Wavelength Audio and XMOS. Meanwhile Meitner's XMOS-powered USB transceiver would include the necessary 'receiver' or firmware changes to recognize such newly repackaged files and play them back as native DSD. 'twas time for me to get busy and into DFF files to test this feature.

In general terms, SACD came, went and failed when the format's inventor Sony withdrew support. Even so SACD players remain current [Esoteric K-01 at right, Ed Meitner's own XDS1 below] and lovers of particularly classical music have quite the inventory of DSD files to sort through*. Now DSD over USB becomes vital. How relevant this late-arriving trickery to support a fading medium for streaming is to you should depend on your present music collection and tastes. This listener never got into SACD or DVD-A for lack of interest in their catalogues. The advent of Studio Masters as PCM files—music recorded at native 24/44.1 or higher resolution—makes it unpredictable just how many listeners will stock up on DSD files from vendors like e-onkyo music, Channel Classic Records and Cybele Records and have/acquire a copasetic DAC. For the vast majority this functionality could really be much ado about nothing.
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* Ripping your own SACD discs is only possible with Sony's PlayStation 3 which can read them raw. But since this copyright bypass requires considerable computer know-how to pull off, for our intents and purposes any mention of DSD here refers exclusively to downloaded digital files.

With a label like Channel Classics owning their own DSD masters, does it make sense to you that their DFF download files should sell for nearly twice what their hybrid SACD discs do? Are we to think the added costs are for server space and bandwidth?


In practical terms DSD over USB is a very clever kludge. It makes DSD do something it wasn't originally intended to do. Stream. Purists might have preferred the raw-data approach but Mac users would have been left out in the cold. With the support of usually competing hardware engineers at dCS, Meitner, Playback Designs and Wavelength Audio, aficionados of the format should consider this DSD repacking scheme sufficient. Future refinements to the open standard will be implemented by way of downloadable updates to the hardware drivers and player softwares (Amarra, Audirvana, PureMusic & Co.). To demonstrate what's involved on the player side of DSD things, I asked Rob Robinson about instructions for his software. Relative to native DSD playback, thinking folks will want to know that Ed Meitner's fully discrete MDAC is the only true 1-bit converter left. Even the dCS RingDAC is a multi-bit affair (today's MDAC is the latest iteration of Ed's original 1-bit Museatex Bidat which launched well prior to the SACD standard).

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