exaU2I - Multi-Channel Asynchronous USB to I2S Interface

[5th element]

Actually what the isolators are doing is effectively breaking a ground loop between the PC and the DAC and it's the ground current circulating within the analogue connectors shielding that is inducing crap into the signal line. You can easily see this as the spikes and its harmonics at multiples of the mains frequency in the non isolated test.

This isn't showing any benefits of isolation on maintaining the integrity of the digital signal, more it's simply showing what a standard ground loop can look like. If you want to see what effect the isolators have you'd need to use a double insulated piece of test equipment that wouldn't form a loop when plugged into the output of the DAC.

[exa065]

Originally Posted by 5th element

Actually what the isolators are doing is effectively breaking a ground loop between the PC and the DAC and it's the ground current circulating within the analogue connectors shielding that is inducing crap into the signal line. You can easily see this as the spikes and its harmonics at multiples of the mains frequency in the non isolated test.

This isn't showing any benefits of isolation on maintaining the integrity of the digital signal, more it's simply showing what a standard ground loop can look like. If you want to see what effect the isolators have you'd need to use a double insulated piece of test equipment that wouldn't form a loop when plugged into the output of the DAC.

Your observations are absolutely correct. The very purpose of the ground insulation is to break the ground loops.

However I disagree that using double isolated measurement equipment will provide more meaningful results. The purpose of this test is to highlight the difference in noise levels when real-world audio equipment is used.

Measurement taken with double-insulated equipment will show less or no difference between the two tests. When real amplifier is connected instead of the measurement tool, the noise will be there.

Note also that in addition to the harmonics of the mains frequency there is high-frequency noise coming from the computer. It is very important that the ground isolation reduces this high-frequency noise.

I would like to explain that the 1 kHz signal at -100dB is used just for visual reference for the noise level. This is necessary because the "measurement equipment" is far from being calibrated. Once you know the scale of the graph, the 1 kHz signal can be turned off.

[5th element]

As my previous response to this wasn't quite what you were happy with I'll try again.

The purpose of the ground isolator isn't to break ground loops but to prevent any high frequency hash from finding its way into the audio circuitry.

High frequency hash wont tend to flow through a ground loop anyway as high frequency currents follow the path of least inductance and you can bet your bottom dollar that down the mains safety earth and through the audio cable shielding isn't that path. It will however help to reduce the effects of any EMI induced currents from flowing.

As you said yourself, the isolator is showing the result of breaking a ground loop, but with it breaking all the traditional crud that can find its way into the loop too. The point of the isolated test equipment would be so that you can show what the isolator does to the performance without the results being impaired by a ground loop.

Preventing a ground loop and isolating the two circuit grounds are completely different things, as you can prevent loops from forming whilst keeping the two circuits coupled. What I'd guess people want to see (at least what I'd be interested in seeing) is the effects of decoupling/breaking the two circuit grounds without anything else happening to join the party, such as a ground loop.

[exa065]

Thank you for posting again. I see where you are coming from and I appreciate your point. This way or the other ground isolation is helpful. For example ground loops are sometime difficult to trace and understand.

[5th element]

I think the ground isolation is a very good idea and in this case is one of the times where you can easily use an isolator to do away with any 'headache' that designing to avoid loops can create.

Usually loops are easy enough to understand in principle, the hard part is often coming up with a complete system design that will prevent them from forming.

[exa065]

I am very excited to introduce a new member of the exa family, the e18 DAC. e18 is not a DIY product, but it is a close relative to the exaU2I. It uses a second generation USB to I2S interface and it can handle 8 channels at 384 kHz. Your support for exaU2I made releasing the e18 possible - thank you!

The e18 will help us to further develop our technology and we will make the advancements available to the DIY community.

You can find out more about the e18 DAC here.

[Bunpei]

Originally Posted by flemming3520

I do not have a source for DSD256 or DSD512 files so I will suggest that you create them from wav files

1) Start with a 176.4kHz wav file : Use Audiogate to resample a 44.1kHz file if needed.
2) In the Wav header change sample frequency and byte rate to 44.1kHz for DSD512 and 88.2kHz for DSD256
3) Use Audiogate to convert to DSD128.
4) In the dff files change the sampling frequency

To flemming3520,

I'd like to express my gratitude to the advice above very much.
Your method easily made me create a DSD256 test audio file!

To exa065,

I think both your exaU2I board and your new DAC must have capabilities of playing DSD256 or DSD512 sources.

Bunpei

[exa065]

Originally Posted by Bunpei

To flemming3520,

I'd like to express my gratitude to the advice above very much.
Your method easily made me create a DSD256 test audio file!

To exa065,

I think both your exaU2I board and your new DAC must have capabilities of playing DSD256 or DSD512 sources.

Bunpei

exaU2I plays DSD128 - DSD512 sources since February 2010. flemming3520 just needed some time to discover it - DSD Playback with exaU2I

In our test environment the exaSound e18 DAC can play 6 channels DSD. We need some extra time to release this feature.

[Bunpei]

Originally Posted by exa065

exaU2I plays DSD128 - DSD512 sources since February 2010. flemming3520 just needed some time to discover it

Oh, that's wonderful!

DCLK for DSD512 is 44.1 x 512 = 22.5792 MHz.
As the exaU2I has 11.2896 MHz oscillator on board, this might mean the FPGA logic includes special 2 x multiplying functionality only for DSD512 sources.

It's really a well-prepared approach!

[exa065]

Originally Posted by Bunpei

Oh, that's wonderful!

DCLK for DSD512 is 44.1 x 512 = 22.5792 MHz.
As the exaU2I has 11.2896 MHz oscillator on board, this might mean the FPGA logic includes special 2 x multiplying functionality only for DSD512 sources.

It's really a well-prepared approach!

DSD came as a gift, Bunpei. It came at no extra charge. This is more than we have expected from our original design. It's really a well-prepared approach!

Happy Holidays!