[alsa-devel] Direct Stream Digital (DSD/DST, One Bit Audio) HDMI pass-trough

[Andrej Falout]

Hello,

I am collecting requirements for implementation a DSD HDMI pass-trough,
according to HDMI specs version 1.2 and 1.3a

I am wondering if anyone previously worked on this, or has any interest in
this functionality.

Any advice or pointers are gratefully received. Here is my list of the core
facts so far:


   1. hda_eld.c in current kernel git ignores raw DSD (One Bit Audio)
   labelled AUDIO_CODING_TYPE_SACD ("SACD" because originally DSD formats
   where only used commercially in SACDs) and compressed DSD (DST) is labelled
   AUDIO_CODING_TYPE_DST (1)
   2. It is my understanding that apart from "special handling" denoted in
   "Table 47 CEA Short Audio Descriptor for Audio Format Codes 9 to 13", (eg
   setting the format code, etc) this should be a reasonably straightforward
   stream pass-trough (2)
   3. Typical use scenario for DSD over HDMI: an DVD/BluRay player that
   supports SACD (Super Audio CD) outputs a DSD stream over HDMI to a DSD
   capable receiver. For instance, my Oppo and Sony BluRay players both do
   that, and all my receivers (Onkyo, Pioneer, Marantz, Yamaha, NAD) have DSD
   DACs and I can play both stereo and surround music this way, without
   converting DSD to PCM. There is currently about 30 million DSD capable
   receivers on the planet, conservatively speaking (Just Onkyo makes 1
   million a year, and makes DSD capable ones since 2003)
   4. Wanted scenario: play DSD files using DSD enabled players (Linux:
   MPD, mplayer, VLC, Squeezeboxserver, etc / Windows: FooBar, JRiver, etc) to
   an HDMI audio card/device on a PC motherboard or add-on video card with
   HDMI, connected via HDMI cable to a DSD enabled receiver/DAC
   5. Note that as far as I know, no proprietary drivers on Windows
   (ATI/AMD, Nvidia, Intel) support this; It will be the first time a device
   that is not a SACD player outputs DSD over HDMI, on any OS. I am assuming
   that this has nothing to do with hardware limitations of the HDMI chips
   used for video outputs (I could not find any reference for such assumption
   in any HDMI chips I examined specs for). Therefore, I assume that
   implementing this has no hardware prerequisites.
   6. DSD format general info:
   http://en.wikipedia.org/wiki/Direct_Stream_Digital  http://dsd-guide.com/
    http://dsd-guide.com/what-dsd-audio-simple-explanation



Thanks,
Andrej Falout

References:
(1)
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/sound/pci/hda/hda_eld.c?id=refs/tags/v3.17
  - Same source file in Alsa GIT tree:

http://git.alsa-project.org/?p=alsa-kernel.git;a=blob;f=sound/pci/hda/hda_eld.c

(2) CEA Standard PDF, page 66, table 47. HDMI specs version 1.3a, pages
72-73 for DSD(One Bit Audio) and DST audio packet header and body formats


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