MPD is not offering any audio output

[eragefe]

Hi dafart Yes the PCB accepts both the Raspberry Pi and the beaglebone black.
You have to attach one of them to the right part of the pcb and the I2S will be transferred to the DAC from the RPi/BBB headers The RPi/BBB ground and the DAC ground will be galvanic isolated from each other.
Due to its compatibility to both RPi and BBB we are not going to call it for a BB cape.
I really don’t want to comment other constructions but as I stated before any kind of ripple on the ground degrades always the sound quality. That’s for sure.
Yes you need a separate chip to reclock. That chip takes also care of the problem with clicks and pops when mpd starts and stops a track. (All of those arm computers are stopping the I2S clocks when you stop playing a track and start all over again when you start playing.)

As I understand it the next version of RuneOs will include the drivers for the HDMI chip. In that case you will automatically get the I2S signals on the BBB header. That’s the case with debian and angstrom distributions for the BBB today.

I will also try to explain why and how NOS in another posting.

BR G

[eragefe]

I probably misunderstood you when you asking if you need a separate chip for reclocking.
That chip is already implemented on the board.

[dafart]

Thanks eragefe for your explanation!

I'm really exited to see how BBB + runeaudio + i2s over HDMI headers will work out..
I don't think enabling the kernel modules and make mpd use the device will be a big problem, we we're not there yet. AFAIK the hifiberry device works (as a DAC) on the RPi with volumio and is capable of bitperfect transport.

Do you also plan on adding extra connectors (digital s/pdif / coax / usb) or do you plan to transport the i2s signal over HDMI?

I just found out that the NAD M51 has hdmi input connectivity and also supports i2s (not really sure if that's i2s over hdmi or over usb)
But if the combination of the BBB with i2s out over hdmi plays fine with an M51 (or any other receiver with hdmi / i2s input support and a DAC built in) than this will be a very potent hi quality / audiophile little media device.
ComPred to all other network streaming devices I've tried, (not so many but still) all those DLNA supporting streamers get really slow when browsing through BIG libraries. MPD is extremely quick and therefor highly potent (for me)
I have not tried NAD's own system (used in the M50 M52 combo) or meriadian sooloos like systems, but IU doubt if they are as fast and responsive as the mpd / mpod is right now..

Good luck!!

Daf

[eragefe]

Hi Daf
I feel that I have to explain a little bit more.
As we say here in Sweden one picture says more than thousand words.
So I made a drawing that explains how it is.
The CPU feeding the HDMI chip with I2S and the chip sends audio+video to the HDMI connector.
You actually are “steeling” the I2S before it reaches the HDMI chip and feeding the DAC.
So we actually don’t use I2S over HDMI but I2S directly from soc.

BR G

[dafart]

Hi eragefe

Thanks for explaining.

So the i2s signal is being transported over hdmi..

That will make it easy to connect to an a/v receiver (though it should support i2s), but when one wants to connect it to a DAC for "pure" audio purposes the available DAC's with HDMI input support are limited.. The NAD M51 is the only one I'm currently aware of..

Or are there hdmi -> coax adapters> Or will that decrease audio quality.


Cheers, daf

[eragefe]

Ok I did some tests yesterday with BBB and I2S.
With the HDMI driver loaded you can get the I2S signals from P9 pins 28 29 31 on BBB.
BUT it seems that every single track you play is being resampled to 48KHz.(NOT bit perfect)
That is not unusual on both windows and Linux but almost unusable for real high end.

I can also say that the I2S from the RPi header IS bit perfect. (I tested tracks on 44.1, 176.4 and 192KHz).

BR G

[ACX]

BUT it seems that every single track you play is being resampled to 48KHz.(NOT bit perfect)

That would be a very bad news if confirmed...
I did a quick Google search, and most of the results were telling the same thing... but maybe there is some hope:
http://permalink.gmane.org/gmane.linux. ... map/110104
In the code you can see this part:

Code: Select all

+static unsigned int tda998x_hdmi_rates[] = {
+   32000,
+   44100,
+   48000,
+   88200,
+   96000,
+};

so it could be possible to get a bit perfect playback from HDMI I2S... at least up to 96000Hz.

[dafart]

Is the resampling an issue with alsa?

Hopefully there is a workaround!

Tia,

Daf

[eragefe]

No no It is not an alsa problem.
My measurements is done with an analog scope so I cant post pictures and as I said the same OS/alsa with RPi works fine.
That has nothing to do with the hardware or the OS. Once again I am not expert on software but I think the problem has to do with the driver I used in my setup when I did the measurements.
It will be easily solved. (It maybe already is).
My setup was
BBB/nelsons debian for bbb/(TI_BeagleBone_B - TI BeagleBone Black) card/MPD/Alsa.
and
RPi/raspbian/(HifiBerry DAC HiFi pcm5102a-hifi-0)/MPD/Alsa

BR G

[Midnight]

BUT it seems that every single track you play is being resampled to 48KHz.(NOT bit perfect)

That would be a very bad news if confirmed...
I did a quick Google search, and most of the results were telling the same thing... but maybe there is some hope:
http://permalink.gmane.org/gmane.linux. ... map/110104
...
so it could be possible to get a bit perfect playback from HDMI I2S... at least up to 96000Hz.

But there is also this description (McASP is an acronym for Multichannel Audio Serial Port, a communication peripheral found in Texas Instruments family of digital signal processors):

McASP produces the bit clock for the i2s bus from
the masted clock by a simple divider and the available sample rates
depend on the used master clock frequency.

So the available sample rates depend on the used CPU frequency?

EDIT: The BBB does not support 44.1 kHz and it's multiples, see this: http://patchwork.ozlabs.org/patch/303984/