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I2S Input?

post #1 of 15
Thread Starter 

I was looking through audio-gd's product page and noticed a few of their DACs offer I2S input now. Having been away from head-fi for awhile I need an update. From I've read 6 months ago, I2S seems better than USB since USB is plagued by jitter. But from what I'm reading on audio-gd's page, it seems like they have solved the issues of USB with new clocks and more direct circuitry. Can anyone clarify and update me on this?

 

Also, how would I physically connect my computer to a DAC via I2S anyway?

post #2 of 15
ohhgourami,I'm also interrested by connecting i2s,I asked this question in the trhead ref 7, but no response
''Is it possible to use the Exadevice with thr Ref 7.1 connects to the DSP or the Interface Digital DSP ,is that nobody has tried, I would like information,please''.
The Exadevice http://www.exadevices.com/Home.aspx , Digital interface USB to i2s a good value,I wanted to know how to connect,you can connect directly to the dsp of ref 7, or does it go through the inteface digital audio gd dsp?????,I think it takes experience feedback.

(traduction google,thanks)
post #3 of 15
Thread Starter 

Nobody?

post #4 of 15
Thread Starter 

Bump? Really no one knows the answer to this?

post #5 of 15

Have you got DIY skills? If you do then you can buy a USB to SPDIF adapter and hack into the I2S lines of the USB chip.

The USB to SPDIF adapters don't do anything to reduce jitter at the DAC input end as it happens. For true low jitter performance from a USB chip you have to go from the chip I2S output into the DAC chip I2S input. Even async USB to SPDIF adapters cannot outperform an adaptive USB chip with I2S output. A brilliant example of that is the ODAC. It is an adaptive USB chip with I2S connection into the DAC chip.
 

post #6 of 15

"Less is more"

 

I2s was invented as a standard for transferring digital data between CD spinnner mechanism and DAC chip(s) inside CD players. Thus all audio DAC chips (that I know of) have I2S input pins. "Wires" of I2S transport can be directly connected to DAC chip - there is no need for other intermediate digital signal conversions (like conversions to and from AES or SPDIF) which is, of course - better. But, as mentioned, I2S was designed as standard for internal digital signal transport, not external. AES and SPDIF were invented for external. Thus I2S signals are susceptible to various interferences and, in general, I2S external cables should be shielded and short.

 

Note that there is no guarantee of better sound with I2S transport. In theory it is the easiest, most elegant way of feeding digital data from transport (computer, digital player...) to DAC chip, but in practice it depends on the implementation (as all other things in audio) of digital data conversion to I2S format and of I2S signal transfer from I2S convertor to DAC chip.

 

In general, we are talking here of USB to I2S converters.

 

Note that on most DACs with USB inputs - the USB inputs are in fact "internal USB to I2S converters". Internal in a sense that the converter is physically located inside DAC and once USB data from it is transformed into I2S signal - this I2S signal has to travel only a few cms to DAC chip which is, very likely, on the same board. Ideal place to put USB to I2S converter/input, no? Yes, but we know that up till recently, almost as a rule DAC USB inputs were blatantly inferior to SPDIF inputs on the same DAC. This demonstrates the importance of quality implementation of USB to I2S converters (converter power supply, clocks, clocks power supply, converter chipset, converter firmware, type of USB transport, converter software drivers...). Fortunately - things are moving for the better and one can foresee USB domination in the future...

 

It is almost the same with external USB to I2S converters. That is - with the additional problem of transferring impeccable I2S signal through I2S output connector (ethernet socket in most cases), through cable (ethernet cable in most cases), DAC's I2S input connector (again ethernet socket) and wires or board traces to DAC chip. See why, all other things equal, internal USB inputs have advantage over their external counterparts?

 

So ohhgourami - to connect your computer to your DAC through I2S you would need some kind of external USB to I2S converter.

 

Or get a DAC with decent USB input.

 

Or even better - get DAC with decent USB input and I2S input. So you can enjoy your music now and try latest and greatest external USB to I2s converters in the future. Those current are either mediocre or shamelessly expensive.

 

BTW, A-GD's latest USB-32 implementation of internal USB to I2S is quite good. I am yet undecided, but NFB-11.32 USB input is in whereabouts of audiophilleo2 connected directly to NFB-11.32 BNC SPDIF input.


Edited by FauDrei - 9/22/12 at 11:40am
post #7 of 15
Thread Starter 

WOW, FauDrei, thanks a lot for the comprehensive explanation!

 

Yup I was reading about audio-gd's USB-32 implementation too and it seems it should be AT LEAST as good as having the DI connected through BNC. I'm just surprised that I2S still isn't all that good. I remember reading how PS Audio was flaunting their I2S implementation last year. Never got a chance to hear their DAC, but I'm guessing I2S for that isn't all that great them.

post #8 of 15

Is there a list of DACs with I2S inputs?

post #9 of 15
Quote:
Originally Posted by ohhgourami View Post From I've read 6 months ago, I2S seems better than USB since USB is plagued by jitter.

It has been overstated in order to sell various miracle cures. Computers are now running at a far faster rate and with better accuracy than several years ago, producing timing accuracies that are good enough for the far slower audio signals. So the USB jitter problem is something from the past that is still used today to sell antiquated solutions.

post #10 of 15
Quote:
Originally Posted by Baxide View Post

It has been overstated in order to sell various miracle cures. Computers are now running at a far faster rate and with better accuracy than several years ago, producing timing accuracies that are good enough for the far slower audio signals. So the USB jitter problem is something from the past that is still used today to sell antiquated solutions.

 

 

Do you have any objective measurements to support this?

post #11 of 15

Bologna, if anything modern usb ports and their controllers are probably cheaper and crappier due to cost cutting.

post #12 of 15

Sure, and it can easily be repeated. Just get something like a M2Tech asynch USB to SPDIF converter and a recent laptop or desktop PC. Get an adapative USB DAC with an SPDIF input. Now get a group of people with good to excellent listening skills. Play music through the M2Tech (other asynch USB adapters are also available and can be used instead) and through the adaptive USB input. Ask your assembled listeners to point out which set up has the jitter and which one hasn't.

Any similar blind test can be conducted between USB devices.

If you repeat the same test with a PC running at say just 1GHz you stand a bit of a chance to pick out the difference in jitter. But once you get past 1.7GHz and use a dual core processor or better, it has so far proven to be impossible in all my trials to get a result that is better than guessing.

One thing that I did find interesting, but which I haven't seen discussed often, is that females were better in hearing a difference.
 

post #13 of 15
Quote:
Originally Posted by Baxide View Post

It has been overstated in order to sell various miracle cures. Computers are now running at a far faster rate and with better accuracy than several years ago, producing timing accuracies that are good enough for the far slower audio signals. So the USB jitter problem is something from the past that is still used today to sell antiquated solutions.

 

Quote:
Originally Posted by preproman View Post

 

 

Do you have any objective measurements to support this?

 

 

There are a number of peer-reviewed papers investigating jitter audibility. Let us ignore anecdotes and dog and pony shows please. Our best state of knowledge is that jitter has to be multiple 10s of ns (correlated)  or 100s of ns (random)  to be audible. The best papers to date are Benjamin and Gannon 1998 and Ashihara et al 2007?. Stereophile has done measurements on jitter on digital components and to date only one component the alarmingly poor McIntosh MS750 Music server has jitter levels close to audibility (14ns). As for USB jitter again Stereophile has measured this on a few devices and afaik the worst usb thing they have measured the original HRT Music Streamer which tops out at 720ps quite poor relatively but not in itself audible bearing in mind that the device measures so apallingly on so many other parameters that jitter would be the last thing you would worry about...

post #14 of 15

Yes there are a number of peer reviews. But all those reviews were written down based on the use of computers and storage media that we would now consider outdated. A modern day PC with SSD storage and an i3 or better processor backed up with DDR3 RAM makes the use of an asynch adapter a waste of time. But why rely on peer reviews? carry out your own test with a group of people and see for yourself how impossible a task it is to decide which audio playback has more jitter than the other.

But even more alarmng is the SPDIF output on these adapters. That SPDIF signal is not subjected to any asynch process and is no better than a straight SPDIF signal from a CD player.
 

post #15 of 15
sorry responded to wrong thread
Edited by scottosan - 12/9/13 at 8:35am
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