SPDIF Cable, longer is better! (Interesting articel)

[manisandher]

From a purely theoretical point of view, I would have thought that DAP-in-XX + 4xOS-in-DAC would have given you the best sound (8x oversampling in total). As Peter said, just DAP-in-XX with filter-off-in-DAC will give lots of HD near the real signal.

With filter-off-in-DAC, I would have thought that the oversampling switches (1x to 8x) would make no difference whatsoever. I mean, the filter is off, after all. And this is what you seem to be finding.

In any event, hopefully DAP + 4xOS is giving you good sound. And count yourself lucky that you have a true multi-bit DAC (i.e. no massive 64x or 128x oversampling) with which to try these things.

If the Ref7 could accept 176.4/192 signals through its BNC input, I think it would make it a very attractive proposition. I bet it'd work really nicely with a BNC-hiFace, XX set to QAP and the filter switched off in the DAC.

Mani.

[Flecko]

I am back to 8xOs. There are "more" highs with 4xOs and it sounds more dynamic (agressiv?) but it is also fartiguing. There is something wrong, something that bothers my ears. 8xOs sounds finer and renders/seperates each instrument more. As always, it needs a little time to judge.

[Flecko]

To be honest, at last, I kicked out ArcPred again. Don't know what was yesterday Maby to sick to hear. ArcPred has something but, there is still the awkwardness... However, now all is back to normal except that I kept the doubling.

[Flecko]

That I don't use ArcPred doesn't make it a bad thing. It is not ment to work that way, it is for NOS-DACs. Justed in case "someone" misunderstands this.

[PeterSt]

Not me !

The more you seriously report on this, the more I will learn from it !

Thanks,
Peter

[Flecko]

Not me ! Happy Happy

The more you seriously report on this, the more I will learn from it !

I actually ment the million $ man

[jkeny]

I just saw this thread now & would like to add my bit to the discussion.

Firstly, long SPDIF cables work by delaying the signal reflections so that they no longer arrive back at the DAC at a critical moment. They do NOT work by reducing the signal or the reflections by any significant amount. The correct length of SPDIF cable has to be calculated - it is no simply a case of all cables over a certain length will work!

Secondly, Rf attenuators work by reducing the SPDIF signal AND by reducing the signal reflections by TWICE (because the reflection has to pass through the attenuator twice on the way to he DAC).

Yes, it is better to have a true 75 ohm impedance all along the SPIF signal path - this includes transmitter, output stage, connectors, cable, receiver input stage. If any of these are not truly 75ohm impedance you will have a signal reflection. So even if you have a well designed impedance controlled DAC, you can't control the reflections arising outside of the DAC.

I believe the RF attenuators are a useful way of reducing these reflections & hence the jitter resulting.

Yes, the Hiface has a high output SPDIF signal which could be considered a flaw but it also allows us to use a higher attenuation & thus a higher reduction of jitter.

BTW, the smoother, more analogue sound reported with using the Rf attenuators is, to my mind, a better, more realistic reproduction of what's on the recording. We often think more pronounced dynamics are better BUT I believe this is one of the mis-conceptions that listening to digital audio has given rise to. We think this is the detail of digital sound but in fact, I believe, it is the distortion of jitter that we are hearing & interpreting as "better dynamics"
 

[Flecko]

The correct length of SPDIF cable has to be calculated - it is no simply a case of all cables over a certain length will work!

That is true. But I think there is also another effect that comes with longer cables and that is very important. The reflected signal is not correlated to the signal if it arrives after a certain time. And that effect, you have simply after a certain length.

So even if you have a well designed impedance controlled DAC, you can't control the reflections arising outside of the DAC.

You can, by using good cables, connectors and a well designed source. You surely not get rid of reflections completely.

I believe the RF attenuators are a useful way of reducing these reflections & hence the jitter resulting. Yes, the Hiface has a high output SPDIF signal which could be considered a flaw but it also allows us to use a higher attenuation & thus a higher reduction of jitter.

Yes, they can have a positiv influence but a well designed dac and source will be better. If you use 12db attenuator (and the dac still locks), the reflections are reduced about 12db. If you have a propper source, you can reduce it about 40db. That is a difference in signal strength of about factor 1000. That means the reflection is 1000 times higher with the attenuator compared to a propper source. It helps, but it is more like using crutches indstead of having healthy legs.

BTW, the smoother, more analogue sound reported with using the Rf attenuators is, to my mind, a better, more realistic reproduction of what's on the recording. We often think more pronounced dynamics are better BUT I believe this is one of the mis-conceptions that listening to digital audio has given rise to. We think this is the detail of digital sound but in fact, I believe, it is the distortion of jitter that we are hearing & interpreting as "better dynamics"

Jep

[jkeny]

That is true. But I think there is also another effect that comes with longer cables and that is very important. The reflected signal is not correlated to the signal if it arrives after a certain time. And that effect, you have simply after a certain length.

You mean it is no longer data correlated jitter?

You can, by using good cables, connectors and a well designed source. You surely not get rid of reflections completely.

Yes, exactly, you cannot get rid of all reflections completely & when you use a device with a faster rise time SPDIF signal (which will be more accurate) you will give rise to even more reflections. So why not use a simple & cheap way to deal with them - attenuators @ $12

Yes, they can have a positiv influence but a well designed dac and source will be better. If you use 12db attenuator (and the dac still locks), the reflections are reduced about 12db. If you have a propper source, you can reduce it about 40db. That is a difference in signal strength of about factor 1000. That means the reflection is 1000 times higher with the attenuator compared to a propper source. It helps, but it is more like using crutches indstead of having healthy legs.

The attenuator reduces the reflections by 24dB in the above example i.e a factor of about 1/16 whereas the signal is reduced by 1/8!
How many well designed transmission lines are there? From the article linked to:

The transmission-line components (excluding the driver, receiver and terminations) include:

The traces on the Transport circuit board that connect to the driver chip
The wiring to the output connector
The output connector jack and plug (BNC or RCA)
The digital cable
The input connector jack and plug at the DAC input (BNC or RCA)
The wiring to the circuit board
The traces on the DAC circuit board that connect to the receiver chip

Any of these individual components may cause a reflection on the transmission line if they are not 75 ohms characteristic impedance. This is why it is insufficient to replace the RCA connectors with BNC’s without addressing the wiring and circuit-board traces that are not 75 ohms characteristic impedance. I have never seen impedance control on any Transport or DAC circuit board. Occasionally, the wiring from the circuit board to the connector is impedance-controlled, but this is the exception, not the rule.

Also lots of people use RCA connectors - attenuators are the only answer to this impedance dilemma, I believe. 

[Flecko]

You mean it is no longer data correlated jitter?

It has still the same footprint but as it arrives some periods later it is not that correlatet to the data anymore as if the reflection comes in the same period of the signal from that it was reflected from. It has a more random character.

The attenuator reduces the reflections by 24dB in the above example i.e ten fold more than the amount that the signal is reduced by! How many well designed DACS are there? Also lots of people use RCA connectors - attenuators are the only answer to this dilemma, I believe. 

You are right but then it is still factor 100. I do not want to say that attenuators are not a good way to reduce reflections for a given system. It just should be done right from the beginning. Instead of using RCA one can install bnc very simple by replacing the in/output jack. But why doing all this if you can get propper designs? It will never become that good.

[jkeny]

It has still the same footprint but as it arrives some periods later it is not that correlatet to the data anymore as if the reflection comes in the same period of the signal from that it was reflected from. It has a more random character.

Yes, good point as data correlated jitter is the most offensive sonically but I don't know if this would be considered random jitter & sonically benign? BTW, a very short cable also answers this way of avoiding reflections arriving during the decision window!

You are right but then it is still factor 100. I do not want to say that attenuators are not a good way to reduce reflections for a given system. It just should be done right from the beginning. Instead of using RCA one can install bnc very simple by replacing the in/output jack. But why doing all this if you can get propper designs? It will never become that good.

Yes but in the case of the Hiface we can go upto about 20dB of attenuation so we have reached your best 1,000 times (40dB) reduction of reflections . That's why I consider the design flaw of the Hiface to be an advantage when using RF attenuators - all for $12, not bad, considering what well designed impedance guaranteed (1%) cable in the lengths suggested would cost (& this is only the cable end of things - a well designed transport & DAC is going to cost you of another wad of money. I'm all for doing it "right" but what is the expense of this?

[Flecko]

Any of these individual components may cause a reflection on the transmission line if they are not 75 ohms characteristic impedance. This is why it is insufficient to replace the RCA connectors with BNC’s without addressing the wiring and circuit-board traces that are not 75 ohms characteristic impedance. I have never seen impedance control on any Transport or DAC circuit board. Occasionally, the wiring from the circuit board to the connector is impedance-controlled, but this is the exception, not the rule.

Normaly the signal gets terminated by a serial resistor. Not the best way, as far as I know , but it is usually done like this. Of course you have to stay with 75ohm for the whole signal chain. I managed to go from the board of my dac to the hiface with 75ohm. The improvement sounded a little like having the attenuator in the signal chain.  It also  should lead to the same characteristics as it improves the same thing.

Yes but in the case of the Hiface we can go upto about 20dB of attenuation so we have reached your best your 1,000 times reduction. That's why I consider the design flaw of the Hiface to be an advantage when using RF attenuators.

Ok, good point and good to know that it works. I had an 6db attenuator in my system. 20db should be even better. But still the hifacde has 45ps jitter figure according to Philip Gruebele. Do you use also better clocks in the hiface mod and can this jitter be reduced due to this?

[jkeny]

Normaly the signal gets terminated by a serial resistor. Not the best way, as far as I know , but it is usually done like this. Of course you have to stay with 75ohm for the whole signal chain. I managed to go from the board of my dac to the hiface with 75ohm. The improvement sounded a little like having the attenuator in the signal chain.  It also  should lead to the same characteristics as it improves the same thing.

Yes, not the best way, so you are immediately settling for less than he ideal - maybe a band-aid is needed ! I doubt you got the same improvement from it as you would with 20dB of attenuation. Have you measured the characteristic impedance of the transmission line?

Yes but in the case of the Hiface we can go upto about 20dB of attenuation so we have reached your best your 1,000 times reduction. That's why I consider the design flaw of the Hiface to be an advantage when using RF attenuators.

Ok, good point and good to know that it works. I had an 6db attenuator in my system. 20db should be even better. But still the hifacde has 45ps jitter figure according to Philip Gruebele. Do you use also better clocks in the hiface mod and can this jitter be reduced due to this?

45pS of jitter on the output of the stock Hiface is damn good - what are you comparing to? I deal with the data correlated jitter in my mods to the Hiface by addressing the PS to the clocks among other things. I haven't had the jitter at the output tested but sonically I can hear a big improvement.

[Flecko]

Yes, not the best way, so you are immediately settling for less than he ideal! I doubt you got the same improvement from it as you would with 20dB of attenuation. Have you measured the characteristic impedance of the transmission line?

No, wish I could But I done it as good as possible. Before it was done really badly. I am sure the attenuator will improve the signal further.

45pS of jitter on the output of the stock Hiface is damn good - what are you comparing to? I deal with the data correlated jitter in my mods to the Hiface by addressing the PS to the clocks among other things. I haven't had the jitter at the output tested but sonically I can hear a big improvement.

It is not bad. Philip Gruebele (audiopilleo) claims for his device 8ps of jitter and Pat from Art even 4ps. And of course Peter with ultra low jitter of 0.5ps. But this are also just numberes and there is more stuff about that jitter problem like clockphase noise that is important. But here I must trust the experts and that they really know what they do. It needs a lot of experience and knowledge to make these things right.

[jkeny]

No, wish I could But I done it as good as possible. Before it was done really badly. I am sure the attenuator will improve the signal further.

That's my point - how do we know if the characteristic impedance of the device is correct? I's not simply a case of putting in a 75ohm R, as you know. You might just have substituted one set of reflections for another

45pS of jitter on the output of the stock Hiface is damn good - what are you comparing to? I deal with the data correlated jitter in my mods to the Hiface by addressing the PS to the clocks among other things. I haven't had the jitter at the output tested but sonically I can hear a big improvement.

It is not bad. Philip Gruebele (audiopilleo) claims for his device 8ps of jitter and Pat from Art even 4ps. And of course Peter with ultra low jitter of 0.5ps. But this are also just numberes and there is more stuff about that jitter problem like clockphase noise that is important. But here I must trust the experts and that they really know what they do. It needs a lot of experience and knowledge to make these things right.

Yes, these are just numbers & as a number of people say it's the type & spectrum of the jitter that is important. So 0.5pS may not be better than 8ps, who knows? Steve Nugent certainly claims that a 2ps clock sounds better than his 0.5ps one. I believe that most of the issues with clocks start with the clock PS - most don't seem to get this right.