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

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There's no question that the differences below -140dB that he measured in the video are completely inaudible. Claiming anything else requires a very carefully constructed and controlled experiment to demonstrate that this "super-human" ability is real -- it's simply beyond any known scientific fact and requires belief and faith, instead.
Yes he did mention that too.

But you know he did mention he hear a different

So i will have to wait and see

Oh and i think i hear a different but I might not pass ABX test too haha
 

pkane

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Yes he did mention that too.

But you know he did mention he hear a different

So i will have to wait and see

Oh and i think i hear a different but I might not pass ABX test too haha
There are many other things to worry about that make a difference that's thousands of times bigger. Worrying about some random jitter component at that level is just silly. And no, at -140dB I guarantee you're not really hearing it.
 

Ashley Salmond

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This is an analysis of I²S interface to see if it is superior to S/PDIF or USB interconnects for audio DACs. From what I recall, it was PS Audio that popularized I²S for external DAC connections. Phillips (now NXP) had invented I²S years early as an internal protocol to route audio. It was not and has not been blessed for external use over cables. This use has been ad-hoc with no real attempt at any kind of standardization. As a result, schemes for external use vary, some use HDMI connectors, others RJ-45 (ethernet) and so on. Even with the same connector, the wiring may not be the same. You can see the HDMI variation of it here in the devices I tested for this review:


Note that despite use of HDMI connector, there is absolutely no compatibility with HDMI as used in video and home theater. All that is in common is use of the connector or cable, not the language spoken over it.

The motivation for I²S instead of S/PDIF serial bus was to separate the clock and with it, provide some kind of benefit. I let Paul McGowan of PS Audio explain it a bit more:


Toward the end he says I²S sounds "considerably better." Does it? It makes intuitive sense that sending out the clock and data separately would be better but we don't design electronics based on lay intuition. If something sounds a lot better, it better darn show up in measurements and hence this article.

Measurements
I wanted to do this study earlier but lose use of the only DAC I had with I²S input. I am fortunately enough to have the Gustard DAC-X26 with has that input and is one of our top performing DACs. As such, it should be good enough to show any benefit from I²S. I also have the Singxer SU-1 which converts USB to I²S. I just reviewed its functionality in generating S/PDIF. For this test, I will be showing how it performs using I²S.

I started by running my usual dashboard with balanced output of the Gustard DAC-X26 connected to my analyzer and input set to I²S and provided by Singxer SU-1. This is what I got:

View attachment 23901

Usually our oscilloscope waveform display on top left is ornamental and not revealing of much. But here, it immediately shows a problem: the two channels are not locked together! There is a phase shift/delay in one channel and hence the reason the Left and Right don't land on top of each other. I added the phase differential meter at the bottom which shows one channel has a delay of 8 degrees! This is not good. A digital to digital interface better be "lossless" in this regard. And what the heck is the benefit of separate clock in I²S is if it causes this kind of skew?

Maybe our DAC is broken. So let's also connect the S/PDIF cable between Singxer SU-1 and DAC-X26 and measure that:
View attachment 23902

Channels are in lock-step as they should be. We will investigate this further but for now, notice that there is no performance improvement with I²S. Differences are run to run variations.

EDIT: Setting mode switch 6 to on fixed the phase delay.

As it happens, I also have a Gustard U12 USB converter which also outputs I²S. So let's wire that up and see what it does:
View attachment 23903

Ah, channels in lock step as they should be. Performance is the same (again, ignore small changes). So while I²S connection doesn't break anything, it doesn't provide any measurable benefit either.

Since the U12 works better, let's use it to run a jitter test, comparing I²S to S/PDIF on the output the Gustard DAC-X26:

View attachment 23904

Again, we have tiny variations but nothing of not let alone a change that is audible.

Conclusions
It is remarkable how as non-technical audiophiles, we quickly play engineer and decide what is technically better. "Oh, the clock is separate in I²S so it must sound better." Do you even know what a clock is? How about clock skew? How about perils of taking a standard for moving an inch or two inside some gear and making it travel dozens of inches externally? You think that doesn't do anything bad?

If you want to use lay assumptions, think of how S/PDIF is decades old and by now, folks have figured out pretty well how to extract the clock out of it and deliver excellent performance. Such is the case here. S/PDIF has universal compatibility to boot which I²S does not have.

So Paul McGowan, please don't spread misinformation about I²S sounding better. Start by showing us measurements that demonstrate anything improving and if so, why PS Audio gear doesn't have good enough S/PDIF performance to need something better. And then, point the camera at yourself, connect both inputs to your DAC and have someone else switch inputs and see if you can tell the difference. Since levels don't change, it is dead simple to conduct a blind test.

Bottom line, please don't rely on fantasies like I²S improving audio performance. Insist on measurements being provided to demonstrate audible change in the output of the DAC -- the thing you hear. Don't accept hand gestures as evidence. And certainly not any appeal to a lay person's intuition as a replacement for proper data providing proof.

I will test I²S more in the future as I get other devices with it in there. For now, don't waste a penny even thinking about it, let alone using it.

------------
As always, questions, comments, recommendations, etc. are welcome.

Went to till the field to plant vegetables and realized my diesel tractor is almost out of fuel. I need money to buy some more. So please donate using:
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Amirm, thank you for the information. I do feel Paul does provide information but you always get the feeling he is coming from a position of self interest.
 
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There are many other things to worry about that make a difference that's thousands of times bigger. Worrying about some random jitter component at that level is just silly. And no, at -140dB I guarantee you're not really hearing it.
Noted
 

BDWoody

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There are many other things to worry about that make a difference that's thousands of times bigger. Worrying about some random jitter component at that level is just silly. And no, at -140dB I guarantee you're not really hearing it.
At a ratio of about an inch to 150 miles (if I got my zeroes right), that's clearly Chuck Norris territory.
 

Zog

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But what if PCIe is worse than USB, and having a USB link in between actually acts to clean it up? When you start believing things like this, where do you stop?
But what if PCIe is better than USB? Also how does having a USB link clean it (whatever 'it' is) up? When you start with mild put-downs where do you stop?
 

Gradius

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But what if PCIe is better than USB? Also how does having a USB link clean it (whatever 'it' is) up? When you start with mild put-downs where do you stop?
USB was never made to be "for audio" (USB audio). Is just a DATA transmitter & receiver. Even today, USB still isn't for audio, and it will probably never be.

PCIe by other hand cannot be external, is way too fast, frequency gets out-of-sync, lossy, etc, very fast with lengh.

USB was used because is very versatile and cheap.
 

Harmonie

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USB was never made to be "for audio" (USB audio). Is just a DATA transmitter & receiver. Even today, USB still isn't for audio, and it will probably never be.

PCIe by other hand cannot be external, is way too fast, frequency gets out-of-sync, lossy, etc, very fast with lengh.

USB was used because is very versatile and cheap.
What is "audio" in terms of data transmission?
 

Gradius

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What is "audio" in terms of data transmission?
Digital audio is much more than simple data transmission.

Audio lies on real-time needs (you ever heared of real-time OS before?), it is also the source of clock/jitter problems, interrupt processes, etc. It is also a protocol.

A very short and simple explanation here:
https://www.soundguys.com/usb-audio-explained-18563/

They did addresses some of USB problem with so called "USB Audio Device Class" definition after 2000, but trust me, it wasn't born (nor made) for audio, that came later.

USB was born just as a replacement for serial port (RS232, RS422, etc), parallel port (printers in general), game port (joysticks), PS/2 port (mouse & keyboard), FireWire (aka i.Link), and a few more.

They needed it to adopt due to high pressure from many audio device makers.

Last specification here:
https://www.usb.org/document-library/usb-audio-devices-rev-30-and-adopters-agreement
 

mansr

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USB was never made to be "for audio" (USB audio). Is just a DATA transmitter & receiver. Even today, USB still isn't for audio, and it will probably never be.
USB is a general-purpose digital interface. It can be used for anything that fits within the available bandwidth, including audio.

PCIe by other hand cannot be external,
Thunderbolt begs to differ.

They did addresses some of USB problem with so called "USB Audio Device Class" definition after 2000, but trust me, it wasn't born (nor made) for audio, that came later.
The audio class was introduced between USB 1.0 and 1.1. Here's a page from the document defining it. Note that none of the contributors listed are Gordon Rankin.
1622889933034.png


Short, simple, and mostly wrong.
 

Gradius

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That one was made for "mundane" use of simple audio, like the mic present on a webcam.

In 1997 many (me included) used a very slow Pentium MMX. I recall perfectly well (before 1997 of course) my old 80486 @ 100MHz (overclocked to 120) could barely play a mp3 @ 128kbit/s, anything better the audio would click, lag, pause, dropout, by a whole A LOT.

It was never meant to be used as hi-fi / high-end quality, specially now with the use of DSD and 96kHz @ 24-bit (called Class 2), for example.

I can see you never programmed a protocol before (I did back in 1987)... USB audio uses Isochronous mode, it causes to drops CRC check every 125µs (USB 2), in other words, the source of jitter, noise, quality loss, etc, etc (and you simply omitted all that on my previous post).

Even asynchronous USB audio is far from perfection.

This just proof USB was NEVER meant for audio. Like it or not.

PS: The worst thing about USB (specially for audio) its his use of shared bandwidth, and shared signal between isochronous, asynchronous and bulk/burst mode transfers almost all at the same time.
 

sq225917

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There's no need for real time audio unless you're video syncing, you can happily buffer audio with zero consequences with a suitably design circuit. It's just data,send it, buffer it, isolate the circuit.

I'm using a 30 year old cd transport via aes I to my dac, no difference between that and usb from a stripped out pc. All you need is competent design.
 

maverickronin

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Whether of not USB was specifically "designed" for audio seems pretty irrelevant when it ends up doing it so well.

When Amir tests a DAC's other inputs it's usually a surprise if they do as well as the USB. More often the jitter is worse on the purpose built for audio coax and optical S/PDIF inputs.
 

Harmonie

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There's no need for real time audio unless you're video syncing, you can happily buffer audio with zero consequences with a suitably design circuit. It's just data,send it, buffer it, isolate the circuit.

I'm using a 30 year old cd transport via aes I to my dac, no difference between that and usb from a stripped out pc. All you need is competent design.
My CD transport is almost same age and I do not have the AES output unfortunately. Would be glad if I could add one though.

1622956735292.png
 
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