Study: Is I²S interface better for DACs than S/PDIF or USB?

[scifi9000]

Point 1) Wait, did I miss something? USB to I2S converter?? Why did you do that? You are supposed to be testing I2S vs USB? What you tested was a USB to I2s converter against USB. So, it can only be worse than USB, or at best, equal to considering you are already going through USB.
Point 2) I think that people are confusing the words "sounds better" as opposed to technically better. I agree with Paul's theory that removing unnecessary multiplexing from a signal should be better, but what he didn't articulate clearly was that you may introduce new problems with clock timing over distance (he mentioned it without explaining it technically). I respect Paul but he does have a vested interest in I2S in this case. As a technical purist, I see technical benefit in I2S, but I would never claim to be able to perceive it with my aging ears.
Point 3) I absolutely respect this site for its attempt to quantify what has been subjective, but by now we have gone beyond the ability to perceive these differences and are moving into obsessive purist ideals, and that is what the USB vs I2S debate is all about, which protocol gets the bits from A to B with the least errors.
Point 4) I would love for this test to be run again without a USB to I2s converter.

 

[scifi9000]

is there a way to capture the bitstream at the end of the process and compare it to the original audio file? That would be quite definitive.

 

[somebodyelse]

is there a way to capture the bitstream at the end of the process and compare it to the original audio file? That would be quite definitive.

Yes. That's effectively what RME's ADI-2 DACs do when you use their Bit Test File. Any computer with a suitable interface would do - say a Pi. It won't tell you much though - all the interfaces are capable of transferring the bits correctly, and the argument becomes about clocking, jitter, ground loops etc. and how they are handled or might affect sound and measurements. Those are really implementation issues, and from time to time we see DACs that have a measurable problem on one interface but not another because of that implementation.

 

[Roland68]

Point 1) Wait, did I miss something? USB to I2S converter?? Why did you do that? You are supposed to be testing I2S vs USB? What you tested was a USB to I2s converter against USB. So, it can only be worse than USB, or at best, equal to considering you are already going through USB.
Point 2) I think that people are confusing the words "sounds better" as opposed to technically better. I agree with Paul's theory that removing unnecessary multiplexing from a signal should be better, but what he didn't articulate clearly was that you may introduce new problems with clock timing over distance (he mentioned it without explaining it technically). I respect Paul but he does have a vested interest in I2S in this case. As a technical purist, I see technical benefit in I2S, but I would never claim to be able to perceive it with my aging ears.
Point 3) I absolutely respect this site for its attempt to quantify what has been subjective, but by now we have gone beyond the ability to perceive these differences and are moving into obsessive purist ideals, and that is what the USB vs I2S debate is all about, which protocol gets the bits from A to B with the least errors.
Point 4) I would love for this test to be run again without a USB to I2s converter.

USB always becomes i2s in conjunction with a DAC.
Nothing was done here other than testing the USB route of a DDC against the USB route of a DAC.
SPDIF/Toslink and AES are also generated from i2s and converted back to i2s in the DAC. This also applies to BT routes to the DAC.

The only thing that would be interesting would be a test with a device that can output i2s without USB. But even there the only difference will be interference/interference in the signal, as @somebodyelse already said.

Bit precise comparisons were made in the 90s with jukebox CD systems for industry, data backup and the music industry and even then there were no problems, not even with a 100 € audio CD player with a digital output. This has also been a solved problem for over 30 years and has since been checked many times by manufacturers, universities and engineers.