DSD audio over USB: an XMOS Reference Design implementation - Page 8 - diyAudio
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Old 24th December 2012, 10:06 AM   #71
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Join Date: Dec 2012
Quote:
Originally Posted by RayCtech View Post
There have not been much response....
Discovered pretty fast that help is not easy to get when Linux and MPD is involved.

So to solve the issues I had to use time I did no have and learn the bits and pieces myself.
Then I discovered that the "specialists" was not as clever as they thought them selves..

Anyway - I have ended up with a ARM based system (at the time beeing a CuBox) and have compiled kernels, MPD and built the debian wheezy base filesystem with debootstrap.
Both the 3.5.2 kernels and MPD 0.18git is tweaked to suit my needs and my ideas of how they should perform and work.
By tweaking I have patched, edited scripts and edited source code to be able to get it right.
The kernel is compiled with everything inside (that I need) and thus there is no external modules.
Due to I have Mac OSX, Windows and Linux systems I have compiled in support for all the filesystems and partition variants I have as both USB 2.0 and SATA / eSATA storage devices can be connected.
The kernel is a PREEMPT with threadirqs and RT priorities on USB 2.0 Audio adapters, MPD etc..
As the ALSA drivers is compiled into the kernel I have optimized the NRPACKS and other settings in the source code / kernel, and as I have removed all debugging and other functions /proc contains only the most basic informations like the ID of the soundcards. And as the base filesystem is as simple as possible there is not installed commands like lsusb or lspci etc..
There is no graphic support as that is also removed from the kernel - so it is a completely headless system.
MPoD / MPaD auto-discovers MPD and local cover art works and can be configured without knowing IP addresses etc..
Only WAV, AIFF, FLAC and DSD (native or converted to PCM) formats is supported.
Playing 44.1k/16bit on the internal SPDIF and two USB Audio 2.0 adapters simultaneously uses only ca. 1% of the 800MHz ARM CPU.

My i5 supertweaked system with 3.2.x RT kernel and stock MPD 0.17.1 are now "retired" and have become a totally quiet and very fast crosscompiler
I've just recieved new CuBox to try with my USB Dac.
I think CuBox is very promising unit.
I would much appreciate if you share your compiled RT image.
Thanks a lot.
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Old 30th May 2014, 02:06 AM   #72
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Join Date: Aug 2012
Do you know which chips between combo384 and wm8741?

many thanks.

http://www.diymania.net/data/chedito..._jZNGnjkWy.jpg

Quote:
Originally Posted by sp502 View Post
Hello all,

I just want to make happy the XMOS USB Audio 2.0 Reference Design owners by announcing
the implementation of the DSD audio over USB open standard (proposed by DCS).
DSD over USB standard bypasses the need for special drivers by using 176.4k/24b PCM samples
to encapsulate DSD data (more info in "Playback of DSD Audio over USB A Suggested Open Standard")

Detailed info and the modified firmware can be found here:
https://www.xcore.com/projects/dsd-audio-over-usb

In a few words:
The board has test points for the I2S signals where you can easily "hijack" the signal
and route it to any external DAC. (it has an on-board DAC that is not DSD friendly)
The implementation outputs DSD signals on the I2S pins with the following mapping:

1. Bit Clock - SCLK

2. Left channel DSD data - LRCK

3. Right channel DSD data - DAC DATA

It has been tested by fellow diyAudio member adelias with a properly modified version of mpd
in combination with a Sabre32 DAC and it works (and sounds) great.

It accepts all sampling rates and changes DSD/I2S on the fly!
In Sabre32 DAC the same pins accept I2S & DSD, so the DAC also changes between I2S and DSD on the fly.

The only serious drawback is that everything at 176.4kHz sampling rate is treated as DSD,
essentially loosing the ability to playback 176.4kHz PCM files. This is temporary until DCS
finalizes the standard. Until then do not try to playback normal PCM files at 176.4kHz!

Enjoy listening DSD audio!
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