Why does SPDIF basically suck?

[mansr]

4 minutes ago, Superdad said:

Between elimination of stages and the ability to slave an internal USB>I2S board to the DAC master clock, there would seem to be very few decent arguments in favor of using an external DDC.  The only valid argument I have ever heard was that the DAC designer's USB (or Ethernet) input did not have enough effort put into it.

A valid reason for an external converter would be if the DAC doesn't have USB at all.

 

S/PDIF also lets you do things like split the signal and feed multiple receivers at the same time. Admittedly not a typical thing to do, but if you do need to, it's possible. With USB it's pretty much impossible.

[mansr]

1 minute ago, Audiophile Neuroscience said:

So, no doubt naively, I am conceptualizing that if the buffer is large enough to hold *all* samples then controlling/synchronizing their flow becomes moot......

How many samples is that? A week's worth? A month? A year?

[mansr]

1 hour ago, Audiophile Neuroscience said:

Hi Mans. I am not challenging you (this time haha) just trying to learn. I gather a bigger buffer is required for a year vs a week. IF my thinking is correct then, I would say that I would be 'happy' if the buffer held enough samples on average to last a full song. Now that may mean a variable pause before each playback but that would be my preference IF it solved jitter (and SQ improved) when using spdif.

How would the DAC know how much to pre-buffer? Nothing in the S/PDIF signal indicates the duration, nor is there any kind of start/stop command.

[mansr]

17 minutes ago, Marcin_gps said:

All DDCs I've tried add coloration - it can be good or bad depending on the system and a DDC, but it's one more component in the chain plus an extra cable. It always alters the sound. 

If one has a clean USB output from a PC (or streamer) and a USB input board in a DAC is done right (a separate PSU, decent clock etc), I don't see a reason to use a DDC. In my system any DDC affects performance negatively. 

Really subtle marketing there.

[mansr]

28 minutes ago, adamdea said:

If you've got enough for 1.5 hour and its rebuffers whenever someone stops playback, see how many complaints you get. My guess would be the square root of bugger all.

 

Incidentally I would have guessed it would be possible in principle to detect whether track changes involved a silence between tracks or whether genuinely gapless plackback was necessary. Only a few live albums and some heavily tracked classical albums actually require this. Many (most?) classcial symphonies are still put on the cd one track per movement.

For most music most people play most of the time rebuffering between tracks would be fine and a relatively short buffer would do.

This all sounds theoretical and impractical but some dac manufacturers seem to have managed a scheme using a buffer to enable the use of a fixed frequency clock.  I seem to remember that naim used  (or claimed they used) a solution of having a variety of different fixed frequency clocks which they matched to the incoming stream. 

I can see that it wouldn't be a satisfying solution in the sense of being guaranteed to work all the time for anything that was thrown at it. But seriously, if I was worried about jitter I would happily sacrifice the ability to listen to 4 hours of absolutely continuous music. without a couple of seconds break.

You're looking at this as a user. I'm looking at it from an engineering point of view. If I were to build a DAC, it would work equally well no matter how it was used. If someone wants to play continuously for a month, that should be possible. Hmm, maybe I should build a DAC. How hard can it be?

[mansr]

9 minutes ago, adamdea said:

I get that. While we are at it,  why have any sort of isochronous transmission mechanism. Even asynch usb seems inelegant -why bother troubling the sending device all the time,

Over the course of the playback, the average transfer rate must equal the playback rate. A buffer at the receiver enables the data transfer to take place in bursts. With USB 2.0 audio class devices, a data burst every 125 μs transfers, at the fixed bus rate of 480 Mbps, all the sample data for that microframe interval. Generally speaking, the larger the receive buffer, the less frequently data bursts are required. Still, no matter how large a buffer is deployed, it will require periodic refilling, be it every 125 μs or once an hour, and if the sender is late, playback will stutter. Smaller, more frequent transfers also reduce latency, which is a good thing. Although music playback is less sensitive to latency than, say, gaming, it still matters in some situations. Suppose you use a software volume control. When you adjust the volume, you expect the change to take effect more or less immediately, not after a minute.

 

9 minutes ago, adamdea said:

and surely we want proper error correction and retransmission?

Define proper. Guaranteed error-free transmission implies unbounded latency, and we can't have that. Instead, we must decide how much latency is acceptable and do a best-effort transfer within that interval. Since low latency is generally desirable, we look at the typical error rate of the link layer and choose a retransmission scheme resulting in an acceptable level of packet loss. With USB, it turns out that errors are extremely rare to begin with, so there is no need for retransmissions. Bulk transfers, which have higher reliability demands, do have retransmission on error at the cost of unbounded latency.

[mansr]

15 minutes ago, adamdea said:

What do you regard as the idea transmission mechanism?

Depends on the requirements. If a single interface was always the best, we wouldn't have so many different ones.

[mansr]

15 minutes ago, adamdea said:

How about for connecting a computer to a dac?

That doesn't really narrow it down.

 

15 minutes ago, adamdea said:

(and btw I'm pretty sure we would have a good few different ones whether one was better or not -cf BNC and rca connectors for s/pdif)

RCA is cheaper. Sometimes that matters more than the slightly better connection provided by BNC.

[mansr]

18 minutes ago, Marcin_gps said:

Replacing a component with sth better always leads to better sound.

Overgeneralisation of the day.

[mansr]

27 minutes ago, Audiophile Neuroscience said:

I gather you don't like JPlay Mans?

I dislike them no more than anyone else selling overpriced miracle components with zero evidence that they make a difference.

 

27 minutes ago, Audiophile Neuroscience said:

If so, we share something in common. I wondered whether you have some association with JRiver (I do not apart from using their software). In fact, who are you? care to share?

I have no association with JRiver or any other company in the audio sector. Recently, I have officially taken on the role as maintainer of Sox. This is mentioned on my profile here. If you want to know more, Google me. I'm not hard to find.

[mansr]

1 minute ago, Audiophile Neuroscience said:

As much as I am not a fan of JPlay or the man in question, I think you guys are reading a tad too much into his statement.

There are a few regulars here, our JPlay friend one of them, whose posts almost invariably have an undertone of "you should all buy my stuff." While I understand the desire to promote one's business, it really has no place in a thread such as this one.

[mansr]

22 minutes ago, adamdea said:

...and I feel like a dumb monoglot

I have to admit to being slightly disappointed (and impressed as hell) that Måns' English does not have the heavy Swedish (?) accent I had imagined in my head when I read his posts.

Did you find a video of me or what?

[mansr]

34 minutes ago, adamdea said:

Is that you optimising for linux on arm at youtube.?

I've done a couple of talks on the topic.

[mansr]

21 minutes ago, Ralf11 said:

S/PDIF solves the galv. isolation problem of USB noise transmittal

Only if it is transformer coupled or optical. Many implementations are not.

[mansr]

8 minutes ago, Audiophile Neuroscience said:

Yeh, in my mind's eye, @mansr was a German middle aged ( or older) man. All I can say now is this very bright young man needs to learn to agree with me more often purely out of respect to his elders .

Young? I don't even get carded in the States any more.

[mansr]

4 minutes ago, Audiophile Neuroscience said:

Haha, I saw (what I thought was) you in a 2012 video about optimizing Linux on ARM.

Such a video does exist.

[mansr]

1 minute ago, Summit said:

What do you mean? All good DDCs have some form of transformer coupling to isolate from the (often noisy) USB source.

Maybe all the good ones do. I was also talking about S/PDIF sources in general, not just USB interfaces.

[mansr]

14 minutes ago, Summit said:

To use the S/PDIF or any other digital interface direct out of a standard computer is never good for SQ and IMO no good example when we are discussing pros and cons of different types of digital interface, on a site named Computer Audiophile.

What about the iFi Nano?

[mansr]

7 minutes ago, Summit said:

It’s not easy to implant GI in a portable battery-powered device. It’s one of the limitations of battery-power and is well known.

Whatever your excuses, it's an "audiophile" USB to S/PDIF bridge without a transformer.

[mansr]

52 minutes ago, Summit said:

Is it?

iFi certainly positions themselves as an audiophile company, and their S/PDIF outputs certainly don't have transformers. Those are indisputable facts.

 

52 minutes ago, Summit said:

Okay use it then I don’t care. It probably go well with the rest of your "hifi" gear.

Oh, we've reached the personal insults stage already.

[mansr]

8 minutes ago, miguelito said:

Actually the statement above is completely neutral. What I am saying is that there's design and there's implementation, and sometimes people make generalized statements about design based on one implementation they have analyzed/listened to. I think my statement is pretty clear.

I think our friend Summit is just looking for a fight.

[mansr]

7 minutes ago, Summit said:

To get upset when someone claim things about other designs; like class D sucks or consumer grade sucks, is okay I guess, but claiming all kind of inaccurate stuff about how S/PDIF or DDCs works is okay?

I said S/PDIF doesn't always have a transformer. That is an accurate statement.

[mansr]

3 minutes ago, Summit said:

And I replied. What do you mean? "All good DDCs have some form of transformer coupling to isolate from the (often noisy) USB source. The $179 Schiit EITR for example has it, so it’s not only implemented in very expansive DDCs. The GI is and has always been one of the pros of a DDC or external renderers."

I see we're playing the no true Scotsman game now.