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What is I2S data ??

Mike in MD

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In the General forum, a comment included a reference to I2S data, which was described as:


"I2S consists of three elements: data, word clock, and bit-rate clock."


Then it was asserted that:


"Although these three signals contain digital information, they are actually ANALOG signals and are subject to much of the same rules that apply to an audio signal passing through a circuit."


Chris has taken a "pass" on this subject. Any audio engineers care to expand on how digital information would act as an analog signal in a DAC information stream ???







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the reason why people would describe I2S as analog is due to the fact it has zero error correction, protocol, etc ( i.e. the bad bits of analog ). The bitclock, for instance is a high(ish) frequency signal that you're transmitting over a distance, and it carries vital timing information. The "analog" aspect comes from the fact that the clock is not quantised ( i.e. it can vary by an infinitely small amount between clocks in the "X" direction), and where the receiver decides the clock is will vary depending on the slew rate of the edges, etc. this is why impedance matching is so critical, as reflections etc. on the line will directly effect the timing in the DAC. Unfortunately, since it was designed as an internal interface, this impedance matching is not specified....


your friendly neighbourhood idiot


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I have read the post, and I am sure this was referred to like this because of the analogue character of the signal. Well, it just *IS* analogue because it is a SIGNAL.


So, if a clock line is to work with a square wave, the less it comes out as a square wave, the more harmonic distortion springs from it.


I could give it all a nice twirl by saying that SPDIF contains the clock as well, but there it is contained as DATA. So, I'd say that is more digital than the clock line of I2S is ...


And to make it confusing ... SPDIF is a pure digital "signal", because it carries data in a digital format. BUT, the way it is transported, is just analogue, because it is a SIGNAL.


Confused, right ?


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The sense that I am getting is that the "promise" that came with the original CDs of "perfect music forever" through digital data is false. Digital music is just as tweaky as analog. Audio engineers will always be developing better ways to decode and stabilize the "bit-perfect" music. There will never be a perfect solution to the DAC process. Sounds like fun to me. :)





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I'm an unashamed digital guy - although there are analog processes involved in playback ( and to a much lesser degree in storage ), the one thing digital gives you is a guarantee in the amplitude domain - you can say, without fear of contradiction that if you play the same piece 1000 times, the samples are the same, and don't get worse the more you play them - indeed, the playback may get better over time as playback technology improves,

NB I'm not saying that the existing material we have is perfect, by any means - the compromises taken in 1984 are still affecting playback today, but I hate the thought of playing stuff causing it to degrade,


Also note, that the "analog-ness" probably doesn't correlate that well in tweak terms to tweaks to say vinyl.......


your friendly neighbourhood idiot


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just makes it more interesting !


Let me throw out one potential tweak. The computer makers probably don't worry about the output impedance of a USB port. For a USB cable going to a DAC, the impedance might be important. Reflections and all. So we might have to develop "transformers" to do an impedance match at the USB port.






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