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I2S on usb?

post #1 of 15
Thread Starter 
Please give to me in novice language. If this information is available as native data, why can't it be transferred to a dac via usb?
post #2 of 15
I2S interface is not designed to carry signal over long lengths of cable.
Also it's very different from typical USB and SPDIF interface, where you have 2 wires (one carrying the data signal and the second carrying the ground).
I2S carries multiple streams of data - bit clock, word clock, master clock (if employed) and one or several multiplexed data lines.
This is pretty much IC (integrated circuit) language, not an Universal Serial Bus.
post #3 of 15
MY understanding is that they are different protocols. The data is the same, but transmitted in different manners.
post #4 of 15
Thread Starter 
So a software solution?
post #5 of 15
As audiofil said, there are difference in the hardware layer too. What I should have said is that the digital audio would be the same, but timing information is incorporated in I2S, which doesn't appear to be the case for usb.
post #6 of 15
I thought the isabellina dac takes the i2s data directly from the usb and uses it. That is suppose to be why the usb input sounds so good. Here is a quote from his website.
USB (optional) that converts directly to I2S to feed the internal DAC chip (no intermediate s/pdif conversion). This input offers optimal sound quality and requires the use of a computer (music server) with a USB port. The power bus from the computer is not used. We instead provide our own clean, on-board +5V line.
post #7 of 15
Originally Posted by KingStyles View Post
I thought the isabellina dac takes the i2s data directly from the usb and uses it. That is suppose to be why the usb input sounds so good. Here is a quote from his website.
In that case the USB chip is right next to the DAC chip, so no long cable length. Higher quality USB input DAC's use opti-isolators to break the connection to the computers ground.
post #8 of 15
the usb i2s module used in my opus DAC
USB in, I2S,spdif or Analog out

The i2s goes to dual WM7841 DACs for fully balanced analog output.

i have since encased this project after experimenting and finding that i like what i heard. it now feeds my beta22
post #9 of 15
Thread Starter 
Is the data on the usb?
post #10 of 15
a google definition

I2S, also known as Inter-IC Sound, Integrated Interchip Sound, or IIS, is an electrical serial bus interface standard used for connecting digital audio devices together. It is most commonly used to carry PCM information between the CD transport and the DAC in a CD player. The I2S bus separates clock and data signals, resulting in a very low jitter connection. Jitter can cause distortion in a digital-to-analog converter. The bus consists of at least three lines:

1. Bit clock line
2. Word clock line (also called word select line or left right clock)
3. And at least one multiplexed data line

You may also find the following lines:

1. Master clock (typical 256 x bitclk)
2. A multiplexed data line for upload
I²S consists, as stated above, of a bit clock, a word select and the data line. The bit clock pulses once for each discrete bit of data on the data lines. The bit clock will operate at a frequency which is a multiple of the sample rate. The bit clock frequency multiplier depends on number of bits per channel, times the number of channels. So, for example, CD Audio with a sample frequency of 44.1kHz, with 32 bits of precision per (2) stereo channels will have a bit clock frequency of 2.8224MHz. The word select clock lets the device know whether channel 1 or channel 2 is currently being sent, since I²S allows two channels to be sent on the same data line. Transitions on the word select clock also serve as a start-of-word indicator. The Word clock line pulses once per Sample, so while the Bit clock runs at some multiple of the sample frequency, the word clock will always match the sample frequency. For a 2 channel (stereo) system, the word clock will be a square wave, with an equal number of Bit clock pulses clocking the data to each channel. In a Mono system, the word clock will pulse one bit clock length to signal the start of the next word, but will no longer be square, rather all Bit clocking transitions will occur with the word clock either high or low.

Standard I²S data is sent from MSB to LSB, starting at the left edge of the word select clock, with one bit clock delay. Transmitting MSB first allows both the Transmitting and Receiving devices to not care what the audio precision of the remote device is. If the Transmitter is sending 32 bits per channel to a device with only 24 bits of internal precision, the Receiver may simply ignore the extra bits of precision by not storing the bits past the 24th bit. Likewise, if the Transmitter is sending 16 bits per channel to a Receiving device with 24 bits of precision, the receiver will simply Zero-fill the missing bits. This feature makes it possible to mix and match components of varying precision without reconfiguration.

There are left justified I²S streams, where there is no bit clock delay and the data starts right on the edge of the word select clock, and there are also right justified I²S streams, where the data lines up with the right edge of the word select clock. These configurations however are not considered standard I²S.

I²S signals can easily be transferred via Ethernet-spec connection hardware (8P8C plugs and jacks, and Cat-5e and above cabling).
post #11 of 15
I think you failed to understand an important point regarding the relation between I2S and USB.

I'll give you a concrete example:
You have an USB DAC (doesn't matter which).
The computer sends PCM data via USB. The DAC takes this PCM data into its' built in receiver chip (let's say it's PCM2702). You cannot have I2S straight from USB, you need to convert it first.
Now that's he exact job our chip has - to convert the PCM data coming from the computer(via USB) into I2S format data - the only format that the rest of the circuit can work with.
I've already explained in my previous post what I2S format consists in (bit clock, word clock, data stream, etc).

Following the I2S stream inside our USB DAC we may see it split: the clock data going to a master clock for re-clocking (to eliminate jitter) and/or to an upsampling chip/circuit for reprocessing.
Having passed this stage the data (still in I2S format) goes into the DAC chip for conversion.

As you can see USB interface is massively different from I2S and they complement each other in order to make PC audio to work.

If you like analogies, here's one (maybe not the best I can think of):
You're kind of asking solutions for playing computer games (e.g the music data) in BIOS (the low level stuff that makes hardware work, e.g. I2S interface)
Or a music player (like Foobar) running in Assembly language.

PS: This is not rocket science and it's rather easy and logical to understand.
A quick homework on your part would have cleared most of the misconceptions or misunderstanding.
post #12 of 15
Thread Starter 
I understand the info you are offering. If I understand this, the optical reader gathers the data from a cd. That data is in I2S format. It is converted to PCM data for use on the usb. The PCM data is fed to a usb receiver in an external dac, through another conversion back to I2S and fed to the dac chip.

So to get I2S service from a USB connection, the conversion has to be built into the external dac.
post #13 of 15
Yes, it is right.
Except for the cd part. CDs have a different language (from I2S and anything else), specified in the Red Book.

Basically you have the PCM data inside a package:

The Red Book specifies the physical parameters and properties of the CD, the optical "stylus" parameters, deviations and error rate, modulation system (eight-to-fourteen modulation, EFM) and error correction (cross-interleaved Reed-Solomon coding, CIRC), and subcode channels and graphics.
(... credits to Wikipedia, it's imposible to reproduce from memory without making grave errors)

Now this CDDA format needs to be translated (by a specialized chip inside a cd-player) into a more readable format which can be anything like:
- UDMA if the optical device is ROM based (cd-rom/dvd-rom)
- SPDIF, if serves as transport only
- I2S (if followed by a DAC stage)

As you can see I2S re-claims it's name - Integrated Interchip Sound, and has to do exclusively with D/A conversion circuits.
post #14 of 15
Thread Starter 
I know the cd is in a different format. I meant that the cd reader sends it's information via I2S to the dac.
post #15 of 15
usb to spdif converters also (often) have an i2s output option.

the AMB y1/y2 series uses a burr brown chip that does output i2s, that is intended to go directly to the dac section but COULD just go to some rj45 or something.
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