Single board computers with I2s: quite agressive sound - diyAudio
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Old 30th December 2015, 12:18 PM   #1
Abra is offline Abra  Hungary
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Default Single board computers with I2s: quite agressive sound

We have tried to change the connection from "SBC with USB and I2S -> USB cable -> USB to I2S XMOS card -> short internal cable -> DAC" to " SBC with USB and I2S -> short internal cable ->DAC". Theoretically the later, shorter solution should be better.

Actually the Cubietruck and Odroid C1+ were tried.

Cubietruck required a small hardware mod to enable stereo I2S, while C1+ started to work immediatelly. Now both of them operates flowlessly with RuneAudio software. Technically at least.

But the sound was quite dissapointing relative to the USB XMOS solution.
Using SBC I2S output with classical music, the piano sounded like hit by a rod, nothing natural was in it. Agressive, plus the mid range was rather missing. Similar result with both of the SBCs.

This can be caused by either a poorly implemented Unix I2S driver, or some hardware issue.

Thanks for any idea how to proceed.
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Old 31st December 2015, 09:54 PM   #2
dmills is offline dmills  United Kingdom
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Well, the driver possibility is easily eliminated by simply taking the bitstream into another I2S port and making sure it decodes correctly (It almost certainally does), Linux audio drivers are not that prone to contain gratuitious 'enhancers' and the like.

The other, possibility is timing, MCLK usually being the critical one, and this can be rather poor on some board designs. How are you handling this signal (and its associated return path)?

Also for that matter, WHY should a shorter solution that is taking a critical clock from the motherboard be expected to be better then one generating the critical clock off the board? Simpler is NOT in general better (Neither is it automatically worse), and a USB peripheral handling all the audio clock generation and pulling the data from the computer as required is entirely believable being better then a afterthought design on a motherboard (They are not always better, but they can be).

I get rather fed up with this belief that a shorter 'signal path' (Awful phrase, ignores about half the action) is a better one, sometimes all that complexity serves a valid purpose.

Regards, Dan.
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Old 1st January 2016, 10:47 AM   #3
Abra is offline Abra  Hungary
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Dan, thank you for your notes.
I agree that shorter path is not automatically better. Unfortunatelly here are two examples. Design and the parts counts a lot. But to dismiss the USB part of the chain seems to be a good idea, just because it is totally unnecessary. USB is widespread on computers, and till now the audio was suited to the computer industry. But now here is solution directly for audio applications. So the question is how to make it better?

The test was done at my electrical engineer audio buddy, he provides the technical part of the project. He has a ES9018S DAC with own master clock, so the MCLK on the SBC seems not critical.

He has an idea what to do, but i decided to ask the community if a ready solution or other ideas exist. Furthermore can anybody to suggest another SBC with better I2S results? Better than an isolated or nonisolated diyinhk XMOS or Amanero.

An Odroid XU4 board is already on the way to try (it has 1.8V I2S output only, but it can be shifted to 3.3V we need). I'm also thinking to get an Intel powered Minnowboard Turbot, maybe they provide a better I2S bus for audio than the ARM jungle.
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Old 1st January 2016, 05:01 PM   #4
dmills is offline dmills  United Kingdom
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How are you phase locking the two master clocks?

Also, be aware that some motherboards only do 48KHz and multiples natively (Check the frequency of the LRCLK), if you are really running a 48K audio stream with a the DAC boards XO free running at a rate suited to 44.1 it will obviously sound awful (Same thin if the hardware only supports 48K and the driver is having to do a simple minded ASRC to get things to work).

Regards, Dan.
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Old 4th January 2016, 04:22 PM   #5
Abra is offline Abra  Hungary
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The boards were tried "as is", without any meassuring or mods to get better results.
I think the boards have separate clock for 44.1x and 48x kind of source, but I'm not sure in it, it should be checked.
When the Odroid XU4 will arrive, we will go on to detect and fix the problem if my EE audio buddy can do it.
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Old 4th January 2016, 08:40 PM   #6
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Abra,I ask the question on the Odroid forum
ODROID Forum • View topic - hardware clock
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Old 5th January 2016, 10:18 AM   #7
Abra is offline Abra  Hungary
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Well done, thank you for the link.
We use an ES9018S DAC currently, which has it's own master clock, the MLCK pin is not even connected.
Congratulation, you have a very nice DAC.

The XU4 is arrived today, we can evaluate it next week.
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Old 7th January 2016, 02:50 AM   #8
Peterma is offline Peterma  Australia
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I use Odroid-C1+ with my audial 1541a dac and it sounds fantastic better than the USB to I2s boards I have used. I am using Odroid Ubuntu image from Hardkernel site.

Last edited by Peterma; 7th January 2016 at 03:00 AM.
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Old 7th January 2016, 09:17 AM   #9
Abra is offline Abra  Hungary
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Thank you for the positive observation based on personal experience. Sure we should check the C+ with the Hardkernel image.

I think you used the 1541A DAC with the master clock of the SBC.
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Old 7th January 2016, 09:24 AM   #10
Abra is offline Abra  Hungary
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Thank you for the positive observation based on personal experience.
Sure we should check the C++ with the Hardkernel image.

What kind of USB->I2S converter do you have?
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