USB audio cracked... finally!

[PeterSt]

Not addressing anyone specifically, but part of the crux :

 

USB was made to USB (as in the verb) and not to play audio over. This means that all contenders in the chain, behave to USB spec, driven by "electrical data". Electrically this also means that one element can quite far depict the behavior of the whole chain. Let's have an example :

 

If we like to control a loudspeaker driver, we must have sufficient current to ...

Now think. I will come up with a small clue in a few minutes. If you have an answer, don't hesitate.

[PeterSt]

9 minutes ago, manisandher said:

... create enough force to move the cone (in the way we want)?

 

No points for you Mani, and what I bolded is too intelligent (you added that later) and does not help you. Haha.

 

14 minutes ago, semente said:

Counter-EMF? 

 

Ricardo, I think you changed something too, or I have "Back EMF" too much in my mind as the phenomenon.

Anyway, 10 out of 10, and 11 out of 10 if you removed the "back" from it.

 

So yes. But now why ?

I am going to grab some coffee.

[PeterSt]

6 minutes ago, semente said:

Apparently it's more than just your average "handshake"...

 

If I look at this longer, it could add additional points.

But if really so and as intended, it is beyond my IQ.

 

But I did not see an answer to my question yet ...

[PeterSt]

Just now, manisandher said:

The problem is that the speaker has mass, so the acceleration is finite... and often too slow to follow the music.

 

Ah Mani, you can do better. Anyway, worth 2 points I'd say.

I am considering deducting a few from Ricardo because maybe he was guessing too much. 

 

All in the "kidding" environment of course. Now let's see :

 

Yes, the cone has mass. And from that perspective there's already current required not to let it overshoot. Thus, voltage is going down again already, but cone has mass and wants to continue. Now put a lot of counter-current and it will be stopped from overshooting.

But with EMF as the keyword, this is not much related ...

 

On a side note, and Mani knows it, my speakers are open baffle, and I seriously walk to the speaker more than once each and every day because I hear a "nature" in the bass and feel how the woofers behave (each to reach at the back of the speaker). This is how I learned how all the Operating Systems behave totally different in the bass region; the one OS lets the woofer move as you perceive the sound in the room, the next OS makes no sense, the other OS shows a deep bass but the woofer does not show a frequency while you know it is there in the other OS ... and so on.

 

So let me emphasize that I am more than quite crazy. But I think it helps audio.

[PeterSt]

So, electromotive force (EMF) ...

 

It is not 100% the thing in order. Think how each motor can also act as an alternator (there's one in your car unless you have a Tesla and it charges the battery).

 

The cone excurts (I think this verb does not exist ?), and likes to come back out of itself (this is a mechanical activity). This in itself creates electricity like the alternator.

 

This electricity / the current of it goes back to the amplifier and now influences the behavior of the amplifier itself.

I think we can generally call this the impedance reactance, to the sence that it is not wrong to think in these terms.

We also know that the impedance of the speaker changes per frequency. So per other frequency, the amplifier is behaving differently because it receives back current from the speaker and the amplifier must fight against it.

The more current, the better it can fight the "back current" (I made up that term). The more current, the more stable the behavior of the whole chain.

The less current, the more a mess the whole chain becomes, because the speaker itself is going to determine more what the amplifier sends "the next round" (the speaker could imply more current back than the amplifier ever sent, which is all related to build up of the wave (when slow the amp can do it) and how sudden it stops (when fast, the driver bursts a lot of current to the amp).

 

 

 

[PeterSt]

When no mechanical activity is in order, there is still a reactance from the other side. All electrical connections have. Thus, the other side reacts, it reacts differently per different frequency and the poor sender has to cope with it all consistently. And oh, what I did not tell yet, is the more current is used, the more reactance is implied from the other side. Just think about the speaker driver's excursion again, and how it coming back from 1" implies more current than it coming back from 1/2".

It starts to be rather complex now.

 

It is clear that with our USB interface we can not reach the transmitter (or transceiver if you like, anyway at the PC's end). It does what it does.

The same counts for the receiver (in the DAC).

Right ?

 

Well, maybe we can after all. See the loudspeaker story. If I change the driver (say to a more efficient one), I will influence the transmitter (amplifier). So hey, I can influence the transmitter !

But wait, if I can influence the transmitter, and it would be for the better, I will influence the receiver just the same.

Or ?

Yes. If the transmitter requires less current to control the receiver, then the receiver itself behaves better.

(watch for the chicken and eggs)

If the receiver behaves better because it wasn't fed so much current in the first place, its reactance variance becomes less.

 

And now notice that here all analogy with the loudspeaker stops, because this is digital and we don't need high or low volume (voltage = current). It only needs to work (pass some thresholds to turn a 0 into a 1 and 1 to 0).

So, we can make the voltage and current implications as low (or as high) as we like, as long as the protocol keeps on working, which means that no bits are allowed to "flip" (be different in the receiver compared to how they were sent by the transmitter). And yes, the lower the voltage the more jitter because of noise (SNR becomes worse), but coincidentally I don't care a hoot in this cable.

 

Well, that was it.

And although I imply a very low voltage, I am not saying that it is working (out) like this.

Not a all. You just don't know. So I only tried to explain how the behavior of the lot can easily change, with the objective of influencing the receiver and beyond, because it is *there* where the sound will change for again various reasons (one of them being jitter and I say it again - in that domain; and how that turns into jitter (or not) requires a book).

 

For the mere unbelievers, please keep in mind that I already do this with software alone. So wouldn't it be more easy for me to do similar with a USB cable ?

Fact is, 3 months ago I did not even think of it.

And tomorrow another day.

[PeterSt]

18 minutes ago, manisandher said:

But isn't that exactly what R meant by 'back-' or 'counter-' EMF?

 

 

What you will have read by now, yes. But the difference is in the quotes. So both are phenomena which exist - they are the same : https://en.wikipedia.org/wiki/Counter-electromotive_force - but if you read into that fairly small page, you see it is about something different really (in my younger days it was a means to control model railroad trains in a better fashion - read that Wiki page and you will see it). But :

 

You now have 8 additional points because it is about countering it. So the quotes make the difference, also for the back, which in my book is about the backfiring of it.

This is all not rocket science for those working with it, but we must recognize that he effects of it are everywhere, as long as we think in terms of reactance which is just disturbance.

 

Maybe I am still full with having piles of speakers in the car when I was 20 and beyond (pick your direction) and that all was heavily distorted when set to loud and I was sure that the speakers were too small. But the salesman in the shop managed to sell me an even larger amplifier (like 1000W instead of 200W) and the problem was solved indeed. Maybe that day I learned the most for my future audio, knowing that I just left electronics highschool because computers just emerged and I went that direction.

It is totally crucial in everything and that's why the example.

[PeterSt]

29 minutes ago, manisandher said:

Thinking about USB...

 

So is it generally about 'compliance'? The Clarixa is low compliance and the Lush high compliance?

 

If you add "for Audio" to it, yes. Because that is what I explicitly did. And I can tell you that this implies some environmental challenges ...

Clairixa should be highly compliant to USB2. But who needs that ? 

[PeterSt]

10 minutes ago, manisandher said:

A bit like... if I wanted a smooth ride over a bumpy road, I'd prefer a car with highly compliant suspension - the ride height would have less variance.

 

Ah, OK. No, that is now how I operate(d). I could say Yes because it will come across nicely, but No.

It reminds me about this though, which was foremost in my head when I started the posting sequence :

 

*Because* all what's USB2 spec should have been made to that spec really (with no guarantee, but still), all behaves in a certain electrical fashion and it is as is. This also counts for your USB interface in the DAC and it also counts for my USB interface in the DAC. Again, nobody anywhere made that for audio, and its behavior will be, say, too noisy because of it. "Too" means : unnecessary. This can all be counter attacked with some more careful thinking, and I don't mean : throw femto clocks at it (which btw I do too but for very different reasons).

 

Guys, it is all so easy if you only stick out your electrical sensors and have a slight degree of ignorance;

With a wink to Alex C. ...what was it all about this Silanna chip you say ? Well, the g-d f* chip never was made for audio (btw, Intona the same). It plainly does not work !!!

(yes, I am getting shouty because of it)

So of course the chip maker does his best, but he failed because the USB2 spec is not an audio spec. And he forgot to look at the errors which can not be corrected in audio.

 

We audiophools abuse USB in-depth. And in aftermath we try to correct it for audio.

Have a nice day.  

 

[PeterSt]

Just now, semente said:

I suspect that you are applying dynamic compression to the signal, @PeterSt

 

With me and my tunnel vision ?

 

Oh boy, writing this, I suddenly see another means of electrical tweak.

But I already had another one, so this is for 2020. 

[PeterSt]

2 hours ago, rickca said:

Peter, you said you can do the same thing as the Lush cable in XXHighEnd.  What software control produces the same effect (or does this give away too much)?

 

Hi Rick - I don't think I said that I can do the same thing by means of software; I said (or tried to say) that the influence the D/A process undergoes can also be done by software. Remember, it can only be the D/A process which is influenced one way or the other, unless we assume flipping bits which we thus NOT assume.

Doing it by software is a very very indirect way with a lot of guessing which causes what; noise as such seems the logical subject to think about, but it is always (spiky) current draw which causes noise (this was dealt with more in the beginning of the thread but now for the receiver's end).

Working on the interface itself, which is part of the transfer of the "noise" (but we really should not think about noise as such) would be the best, but useless because it is not what is common to each system for physical aspects. The cable we use is though ...

And to keep in mind (also said in this thread somewhere) : the ideas for this sprung from me working on the finalization of the outboard Phisolator in "re-gen" fahsion, which Uptone already came up with first, as a sheer alternative (I announced this literally on the Phasure forum). And a month or so later it worked.

 

We can say that the little current spikes from a CPU always performing different tasks won't be able to influence much, but then I'd have to remind people about the ~120W a PC comsumes in normal circumstances vs the 30W the very same (20 core hyperthreaded) PC consumes with the for audio "minimized" Operating System. 90 Watts ??? (of difference).

It must be one big mess of bouncing ground planes in there. Call it noise, but ... we were talking about poor little tiny transmitter chips with fragile wave form.

 

Not sure yet whether I am going to sell software or Phasure Stealth PCs today. But probably nothing because I am busy. 

[PeterSt]

Just now, semente said:

I don't use a USB connection but am still interested in the topic.

What should I do

 

Get yourself the cheapest DAC with USB interface available and proceed from there ?

 

(not sure how serious you are with your question )

[PeterSt]

Just now, semente said:

 

 

I have been waiting for my bespoke PCM NOS DAC for ages but it seems that the builder has other things in hand...

 

Ehm ... Which one would that be ? (somehow I am getting anxious)

[PeterSt]

@semente

[PeterSt]

20 minutes ago, Narcissus said:

BG's considered the holy grail of caps, you might find some if you're lucky and know where to look for em.

 

A funny thing is that we could not find real proof of that - only the opposite. People often upgrade their NOS1 with them (in all sorts of places I might add) and as often those DACs measure considerably worse. So mind you, this is thus even measurable, while most is not at all. So it must make a real difference, somewhere. And then to think that we originally use :

 

22 minutes ago, Narcissus said:

Elna Silmic II might be the cheaper alternative.

 

[PeterSt]

26 minutes ago, mmerrill99 said:

Self-noise generated within shift regs, FPGAs, etc do NOT "generate a constant level of noise at the ground plane" - the noise mirrors the processing & if this is a routine regular signal being processed then the noise will have this characteristic i.e noise will be deterministic.

 

I think that many people may have a hard time grasping what "noise" actually is and what its source is. Now let me try to explain it like this (it is a large detour beyond the real subject but it may help) :

 

USB is packeted. The contents of a packet is not known in advance; It is determined by the operating system, even on ad-hoc basis.

The receipt / reception of the packet(s) in the in-DAC USB receiver, requires the current needed to receive one burst of bits, implied by the packet size. This means :

a. that the current required is always changing and that a not really random pattern implies an SQ flavor;

b. it even depends on the music data itself, because the sequence of 1's vs 0's imply different current spikes.

 

Ad b. : I could show you the data correlated jitter of this, when no galvanic isolation would be in i2s. So this part is solved by that isolation ? maybe because my gear can not measure better than 3ps(p-p). Thus maybe not. 

 

If this is understood (and accepted) you could be ready for me showing you the capture by microphone of music sounding through i2s alone. So mind you, that too is noise. But it is highly correlated to what comes from it after the D/A conversion (analogue signal). So we have all kind of 010010000100010100100001 digital data, and it really produces music. One thing : it must be attenuated by 136dBFS to sound the loudest and the best to music because then all bits will be zero except for the least significant bit. Call it the complement of super dither.

And of course it is a D/A converter without D/A conversion.

This is thus noise which is caused just by the changing one one bit and you will be able to hear the real music of it through the speaker. You can of course figure that in reality this implies distortion. Plus, when all of the bits play (no digital attenuation) it will be quite messy.

[PeterSt]

20 minutes ago, pkane2001 said:

I thought that's exactly what I've been talking about -- noise generated by incoming jitter. I suggest you go back and read what I actually said.

 

I only read this after my previous post, and now I am sorry I included a text about jitter in it. So of you skip that part and only read the "i2s music" part you are where I and Merrill want you to be.

Also keep in mind, that in my first posts in this thread I have been repeatedly (kind of) claiming that I regard jitter in USB about completely irrelevant. But still a little about that in a next post.

[PeterSt]

Just now, PeterSt said:

Also keep in mind, that in my first posts in this thread I have been repeatedly (kind of) claiming that I regard jitter in USB about completely irrelevant. But still a little about that in a next post.

 

"about irrelevant" because you now should be able to reflect with the noise coming from the packets, as I just explained. So, you now know that bursts of packets imply current draw, at irregular interval and therefore the noise of it becoming deterministic (expensive word for making the frequencies of it visible). OK ...

 

Now let's think the exact other way around, and the stream of current spikes needed would be nicely even and although there could be a frequency of it visible, it is one frequency only, plus it is of low level because no "bursting" is in order and the current requirement is spread over all the bits (and lets assume it is all 1-0-1-0-1-0-1-0-1-0 etc.).

Next up is jitter in that digital data ...

 

The 0's and 1's are still nicely interpreted and no bits flip. However :

The trigger point on the slopes of that signal is now higher and lower *because* it is jitter doing that (this may require some choking thinking, so think about it). Meanwhile, because the trigger is at the e.g. higher point of the slope, the current force required to get the slope where it is, has already been accomplished. This is how what's triggered itself, starts to prevail on the current draw.

So what I say here is that to get the slope all the way up right from the base might require 5mA and at the normal trigger point is still requires 1mA to proceed to its peak. With jitter, and the slope being a bit higher already, it requires 0.9mA only (so if we see it as a constant draw, it is 0.9mA at that point).

Now comes our trigger, and whatever it is what is triggered, it requires 0.2mA ...

 

It should be obvious in this example that when the constant current draw is 1mA that 0.2mA is 20% of that;

when the constant draw is 0.9mA the 0.2mA is 22.2%.

 

So in this example the impact on the current of what is triggered, varies 4.4% because of jitter.

And now we have the deterministic noise again.

And the rest.

 

I hope you can see that nobody in the world will be able to really work with this, because it is a complex which is, well, too complex. With the last example I assumed 1-0-1-0-1-0-1-0 etc., which already is not so and it largely will debunk my example because of it. Still my story will be true and it all depends on oscillating patterns.

And patterns are the things we hear as flavors.

 

[PeterSt]

11 minutes ago, mansr said:

Is this supposed overshoot real?

 

Wouldn't it be so that any wire (or other bottleneck) which is too bandwidth limited for what the signal wants to accomplish (like infinite rise time or something - haha) ... will exhibit overshoot (and ring) ?

[PeterSt]

20 minutes ago, pkane2001 said:

Thanks, Peter. I appreciate you trying to provide an explanation. But, isn't trigger point driven by the voltage level? Wouldn't it trigger at the same level, regardless of slope? The only difference due to jitter is the timing of this trigger, not the amount of current drawn.

 

You are 100% correct. I got myself mixed up with a slightly different story about the rise time, but  tried to avoid that.

Not sure how to correct this so all doesn't get confusing even more. So wait a bit ...

[PeterSt]

3 minutes ago, marce said:

Without actually taking a look at the waveforms of the system in question it is just guessing though at whether there is ringing... Then you have to determine how much extra noise a bit of ringing (easily tamed) is causing.

 

Marce, can you tell me what you would see when you try to squeeze a square wave (which is supposed to have a close infinite frequency for a close to infinitely short rise time) through a too low bandwidth cable ?

There is no hidden question here and *you* are the HF designer.

"Chaos" would count as an answer, but maybe there is more between black and white.

[PeterSt]

1 hour ago, pkane2001 said:

Thanks, Peter. I appreciate you trying to provide an explanation. But, isn't trigger point driven by the voltage level? Wouldn't it trigger at the same level, regardless of slope? The only difference due to jitter is the timing of this trigger, not the amount of current drawn.

 

So with apologies and ...

 

36 minutes ago, PeterSt said:

You are 100% correct. I got myself mixed up with a slightly different story about the rise time, but  tried to avoid that.

Not sure how to correct this so all doesn't get confusing even more. So wait a bit ...

 

I hope to be able to undo the damage ...

 

When the rise time is steep, there is a certain relation between the current still needed to let rise the wave to its maximum level. Of course it is so that the trigger point (could be 0.8V on a total of 2V)  has this relation to the result of the trigger itself (implying 0.2A in my earlier example). Nothing wrong there yet.

 

But since the subject is the rise time and what it can imply, it can nicely try to avoid this, but of course this doesn't work out because indeed we can not see that the trigger point will be higher for an unknown reason. It isn't (and my example went in the wrong direction there).

So, incorporating the rise time after all :

 

When the rise time now is higher than before (to talk in the realm of the earlier example), there will be more voltage needed to get it at its highest point (still no change in the story), BUT the trigger will be earlier for th rising edge and later for the falling edge. Btw, no jitter again - it is not (additionally or less) there and it is not related.

From here the story is the same, as it is more about the relation to the "continuous" current draw is changed again.

To have it more clear, now compare with the sine; the trigger point is still at the same (voltage level) but later on the rising edge and earlier on the falling edge (eye must stay sufficiently open of course) but the current draw is way less; now the trigger and what it implies has huge impact (relatively).

 

[PeterSt]

1 minute ago, mmerrill99 said:

Overshoot or ringing will not result in an eye pattern that breaches a USB 2.0 eye mask which is one of the main tests for USB conformance.

 

I don't think it is of any real relevance, but if there is high ringing, it will narrow the eye vertically and if you now also have a narrow width, then you have a problem.

So a narrow width may not be too narrow, while additional ringing may shut down the connection (so to speak).

So ringing itself should be OK just the same. Maybe there's a "just in case" in order, but I don't think Marce will agree with that. It just has to bee "good".

 

Now see how Chinese USB2 cables are twisted, sometimes. 

And thus also see that a "just in case" is in order at least somewhere, because the whole chain is not controlled by one instance. PC should be fine, USB receiver at the other end should be fine, but our cables are not under anyone's control (well, virtually).

 

And so, as usual, everything matters.

[PeterSt]

41 minutes ago, mmerrill99 said:

The ringing after an overshoot usually doesn't encroach on the eye mask

 

I had a relatively graduate slope in mind. But this is exactly where ringing (overshoot) does *not* occur.

Thanks.

[PeterSt]

19 minutes ago, jabbr said:

@PeterSt is being understandably coy about discussing what the cable actually does and I suspect his "explanations" are not designed to be precise such that the IP could be copied. As such we are playing a mind reading guessing game.

 

This is not entirely true as I am not of the misleading kind.

What is important though is that matters are being discussed which may be relevant or not (and this is what I can see but don't tell quickly, unless things get out of hand).

 

I am learning here just the same from about anyone who posts. And if someone thinks I know it all, he has it wrong.

But the cable was made very explicitly like it is ...