USB Audio vs. I2S

USB Audio is the easiest and most common method of connecting a server or computer to an outboard DAC. What about this "new" format, I2S?

[IKnewMickey]

Sometimes I watch these videos not knowing what Paul is talking about. This is one of those videos.

[BlankBrain]

I2S (Inter-IC Sound) is an inter-chip standard that has been co-opted to transport audio data between devices. In fact, LVDS (Low-voltage differential signaling) is commonly used to actually transport the signals. HDMI cables provide enough twisted pairs and shielding to pass the I2S signals. One of the really cool aspects of using I2S is that the master clock can be transmitted or received to synchronize everything.

[ThinkingBetter]

USB is a flexible TWO WAY data connection that can do everything data and allows a DAC to PULL data ASYNCHRONOUSLY with its clock in full control (no audible jitter and bit-perfect audio is possible). The computer can identify a device capabilities through USB. An I2S bus is very low level and is SYNCHRONOUS involving a defined clock master. One doesn't sound better than the other one if the audio specs are the same because you can assume that every 1 and 0 come through reliably. My usual concern with USB is any power or digital noise from a PC leaking through to an analog signal. But this is an issue of good design and not USB itself. Think of it like this, your DAC is happy if it gets every bit correctly, it can run the timing in full control (avoid jitter) and there is no EMI or power rail carried noise disturbing the analog output stage. USB is not a limiting factor.

[PebblesChan]

I2S is a bidirectional digital signalling interface between a microprocessor or equivalent like an FPGA to an audio CODEC integrated circuit. In its standard form it is for very short distances like the iPhone or Raspberry Pi to its analog headphone CODEC. PS Audio use it for inter audio component communications. However in many cases, the data is clocked to CODECs as numeric values like PCM. Data across I2S can be specified and interpreted anyway one wants. You can use the I2S interface can be used to send PDM (pulse code modulation) but to ensure accuracy the master clock must have low jitter.

USB is multi peripheral interface protocol and associated physical media that is like a small network. Data is encapsulated with metadata which has to be stripped off to read it.

[BlackFighter_]

USB = No Audio Quality influence of the USB source as the transmission is digital and block wise (e.g. every 1ms all data gets transmitted for the next 1ms).
I2S = Digital data Transmission every sample. The Clock Jitter of the I2S source has an effect on the audio quality. Think of a digital voltage, but the time is "analog". (Even at 192kHz, inter modulation products can be audible)
=> The more devices are in series, the worse a I2S signal gets. USB does not degrade the signal.

Both I2S and USB conduct digital or mains interference from the source to the receiver. A well designed receiver (rarely the case) does not suffer from such interference.
So far USB looks better, BUT as I2S is only used for audio and USB is mostly designed as cost efficient as possible, the interference over USB is often far worse.
Chances are high that the supply voltage of the I2S source is more stable than the supply voltage of the USB.
As a result: With a good receiver you can use both, but preferably USB. On a bad or average (non-HIFI) receiver, you should try I2S. NEVER feed I2S to a HIFI DAC if you can use USB.

[andydelle]

Paul, you fail to mention the major engineering pitfall of high speed parallel interfaces. Timing Skew. I2S is a parallel interface. You have four signals that all have to stay within a relative timing window. The fact that the data signal in I2S is serial does not relieve this requirement. The master clock is typically 24mhz and requires good rise and fall times to meet the timing skew window. Then you have the issue of switching. I2S needs four layers of crosspoints with a minimum 50mhz bandwidth to carry the master clock. That's expensive if say you want to offer three I2S Inputs on a DAC. There is no free lunch and I2S as an external interconnect interface is not the panacea many audio reviewers claim. Yes, you do reduce the jitter inherent in the SPDIF/AES Manchester encoding, but you now induce new and different problems which can have equally detrimental sonic effects. Telecommunication engineers understand this well.

[QoraxAudio]

The funny thing is, even cheap CD players use IsquaredS as interface between the transport and internal DAC.

[isaacsykes]

Hey Paul can you please provide a link to the CD cases...thank you!

[dandonna]

How many PS. audio engineers does it take to put a cd rack together?

[js]

After using I2S, I'll never use usb again! It's so much more detailed! This is from the inexpensive $56 Douk Audio converter that reclocks the USB signal to I2S and a standard HDMI cable. I'm totally sold; this is superior after hearing it. I'm hearing things I've never heard before.

[rightslot]

Hello Paul, This comment is really more related to yesterday's thoughts and explanations than anything. I really like how you are still enchanted about the MAGIC that audio music can bring. 'Cause that is what it really is all about. Sometimes we don't need to know every stinking tidbit. {sometimes...} I had some friends back in college----Engineering (Colorado-Boulder). Sometimes these guys got so wound in the technical and scientific side, they didn't enjoy just a good long night of listening. YOU seem to have not lost that. Great Channel!

[larsv]

What about that hyped USB implementation in the Holo Audio May and Spring KTE? Is that close to i2s?

[joseauger]

But what about DDC (digital to digital converters)? Many, like the Denafrips Gaia that converts USB signal to I2S and has internal oven controlled clocks. If you have a streamer and want to stream high quality digital, like 384k PCM or 512 dsd, you can’t use the SPDIF or AES/EBU output and must use the USB output. The DDC will convert the USB signal to I2S and has opto galvanic isolation. Doesn’t that solve the USB problem?

[mikelm]

Hola May DAC ( The best ever measured by Stereophile ) have both HDMI I2S & USB inputs - everyone agrees that USB sounds best - just saying :-)

[AngryChineseWoman]

You say I2S > USB, but have you taken into account audiophile USB cards, reclockers and galvanic isolators ? Cause they make USB sound so much better. It sure is more expensive, but I'm curious to know how cleaned USB sounds compared to I2S.

[wilcalint]

Paul needs to go back into his lab and do some new testing.

Released in 1986, 34 years ago, an I2S data stream can carry one or two channels of data with a typical bit clock rate between 512 kHz, for an 8 kHz sampling rate, and 12.288 MHz, for a 192 kHz sampling rate.

USB 3.1 Gen 1 (released in July 2013) is capable of data transfer speeds up to 5Gbps. You can't buy a computer these days without a USB 3.1 interface on it. Gen 2 will be capable of 10Gbps.

So that makes USB 3.1 Gen 1 at least 500x faster and 27 years newer then I2S. I think Paul, in this video is refering to USB 2.x or older.

There is no specific i2S connecton on a Raspberry Pi, but using software, and the pin header, you can create what is called a "HiFiBerry". Paul mentioning this makes me wonder if PS Audio has a project using the Raspberry Pi. I use a Pi running KODI for my Multimedia player including HiDef Audio. On my Fedora boxes I use VLC.

[jay]

I do have a question Paul, between I2s or Fiber optic using SFP Port or Dante is the best or lowest noise ?

[NeilDSouza]

I saw a Freddie Hubbard Poster in the Cupboard

[damianox]

I have a smartphone with dsp and dac with i2s interface. This phone sounds better than many expensive desk audio. I think the world is crazy choose USB.

[NeilDSouza]

Luigi : I2S = Spongebob Square Pants
USB = Squidward