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Why digital seems to be affected by power and cables

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rollo, enjoy your Mad Scientist SPDIF even though it is not 75ohm impedance :)

Edited by Ping

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Correct me if I'm wrong that the mad scientist reflections rather than 75 Ohms matters more. Got me. We used a CEC01 transport and a Weiss Medea DAC. No rubbish there.

     It appears for reasons I just do not know the MS cable just was better sound all around. The rest of the system are Pipedream speakers, Arion class "D" hybrid with Duelund output caps, a Loesch & weisner preamp, Kuzma TT, Triode Wire Labs cabling except digital, Lector CDP and a BSG QOL.

 

 

charles

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Well, I have just read 8 pages of mostly O/T dribble here.  Disappointing.

 

 

I was really hoping to learn something significant and "usable" on this subject and it was only in post  #192 that I found something remotely close.

 

There must be more to it than that though, as Craig clearly demonstrated in his 75 ohm connector comparison pics.

Sure, we don't listen to sine waves, (I am in the andyr camp there) but those results cannot be ignored!  They are real and we will hear the result with our ears.

 

But Craig - if SPDIF and I2S are both flawed, what is a better direction to head in?

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But Craig - if SPDIF I2S, {USB, AES/EBU, and etc} are flawed, what is a better direction to head in?

Post #1 and #192 and a couple of others but this is a forum ... so, all good :)

Edited by Ping

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Have you been reading anything I have been saying on this?

 

Definitely signing out

Thanks for your efforts Craig. I have learned a lot from your informed posts.

Kevin

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Yes, I agree Kevin.  I hope Craig comes back, many thanks for sharing your knowledge.

 

I didn't get the opportunity of a uni degree, but Craig explained things clearly so that even I could get a good grasp on what he was saying.

 

Certainly not an intellectual snob either,  unlike some that also have unquestionable qualifications and many letters behind their names, yet display a will to be argumentative and brow beat us diyers that wish to learn more and do a few things for ourselves.

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OK - I'm giving it a second try.

 

i2s was originally only intended for communication over very short distance, between IC's inside a common chassis.  That might just be signals on a circuit board, or a very short cable connection between circuit boards.  That was Philip's intent when they specified the standard - a common inter-chip protocol for audio use.  It is unbalanced, and does not have a defined connector or impedance - which is fine and dandy provided the connection length is a few cm.  To drive a decent length of cable needs all the usual precautions - balanced differential with enough current drive to handle cable capacitance for both of data and clock lines, a defined cable impedance, and *true* resistive impedance matching to prevent reflections.  This http://www.ti.com/lit/an/slyt441/slyt441.pdf is a good primer on how to do it right.  I don't think that most companies do that though.  Personally I would follow TI's recipe, but galvanically isolate each end too.  Done properly i2s as an audio link should work OK, and has the benefit of clock signal separate from the data, so no PLL's for clock recovery.

 

I'm much more ambilvalent about USB.  It was never really intended for audio use - it was designed as a method of reducing the vast array of connectors on a computer back panel, and hence has generic application.  So it is for connecting a mouse, stick, external drive, plus audio (since it is just a datastream, right?).  It can deliver data at a truly scary rate (have a look at what USB3 can handle).  And although the signalling is differential, the clock is embedded in a similar way to SPDIF, with the additional difficulty that you have to use specialist data handling chips usually with a microcontroller strapped on them (embedded on many chips).  And you are limited to fairly short cables - 3 metres is a practical maximum.

 

AES/EBU (Audio Engineering Society/European Broadcast Union) is a differential version of SPDIF, and was designed as the standard for professional audio.  It is 110 ohms (rather than 75 for SPDIF), and uses an XLR connector.  Of course an XLR, from whatever source, is nothing like 110 ohms, so the standard is fundamentally flawed in that sense.  Personally I don't think that it has anything additional to offer as compared with *properly* implemented SPDIF.

 

So for a robust link that should work fine, either **properly** implemented SPDIF or i2s should be the preferred methods.  At least for me.  Of course, because everyone wants every method of doing a digital link on gear there is usually Firewire (and whatever the current Apple standard is, I forget the name), AES/EBU, SPDIF, optical TOS (ugh), and USB, more often than not all imperfectly implemented.

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CraigS, re the 37ohm spdif, what Transmission Line issues do you expect to occur...

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And although the signalling is differential, the clock is embedded in a similar way to SPDIF

 

... sure, but you don't have to USE that clock   (additional complexity, of course)

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AES/EBU (Audio Engineering Society/European Broadcast Union) is a differential version of SPDIF, and was designed as the standard for professional audio.  It is 110 ohms (rather than 75 for SPDIF), and uses an XLR connector.  Of course an XLR, from whatever source, is nothing like 110 ohms, so the standard is fundamentally flawed in that sense.  Personally I don't think that it has anything additional to offer as compared with *properly* implemented SPDIF.

 

Pretty sure there is allowance for rj45 in place of the xlr connectors on aes/ebu cables in the standards somewhere, just most don't use it.

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Pretty sure there is allowance for rj45 in place of the xlr connectors on aes/ebu cables in the standards somewhere, just most don't use it.

 

From the Standard "The standard connector for both outputs and inputs shall be the circular latching three-pin connector described in IEC 60268-12 (this type of connector is normally called "XLR")." https://tech.ebu.ch/docs/tech/tech3250.pdf , which is the most recent version of the AES/EBU standard.

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... sure, but you don't have to USE that clock   (additional complexity, of course)

 

Pardon me?  How are you going to extract the data without a clock?

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Pardon me?  How are you going to extract the data without a clock?

You can use the clock for extraction of the DATA but not use that clock for the Digital-to-Analogue conversion.

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From the Standard "The standard connector for both outputs and inputs shall be the circular latching three-pin connector described in IEC 60268-12 (this type of connector is normally called "XLR")." https://tech.ebu.ch/docs/tech/tech3250.pdf , which is the most recent version of the AES/EBU standard.

I picked it up from this Rane application note  I think - http://www.rane.com/note149.html - looking at it now Cat 5 is down as 'connector' when really it is the cable type and rj45 is the connector. Regardless there seems to be some people at least thinking about doing aes/ebu with connectors that allow much closer to 110ohm connection.

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Please excuse my ignorance here, but why is "75 ohms" the magic figure?

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The last reference is intended to sell AMR's product, and figure 1 shows a truly dreadful SPDIF signal.  However their basic approach is valid - to isolate the digital input circuit (which can generate kick-back) using an wide bandwidth amplifier - their so-called HDâ€Valve Digital Input.  I've been thinking along the same lines, and bought a number of different high bandwidth video amplifiers some time ago.  One of the multiply lined up projects!

 

Pretty sure there is allowance for rj45 in place of the xlr connectors on aes/ebu cables in the standards somewhere, just most don't use it.

 

Colour me surprised - you're right.  Although EBU's latest documents do not specify anything other than XLR, the AES seem to.  Now it is impossible to download AES documents unless you are a member of the AES (I'm not), but there is some abstracted information here http://www.digitalpreservation.gov/formats/fdd/fdd000142.shtml .  And this says:

 

"The main body of AES3 specifies signal transmission via a single shielded twisted wire pair. Annex D, however, discusses the carriage of AES3 signals on structured wiring, e.g., the "category 5" cables associated with computer network installations, a topic that receives extended treatment in AES47, which specifies the method of carrying multiple channels of audio in linear PCM or AES3 format across an asynchronous transfer mode (ATM) network. Elaborations on audio signal transfer are the topics of AES10-2003, AES Recommended Practice for Digital Audio Engineering 8221; Serial Multichannel Audio Digital Interface (MADI) (Revision of AES10-1991), and AES50-2005: AES standard for digital audio engineering 8221; High-resolution multi-channel audio interconnection."

 

Which does allow for CAT5.

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Please excuse my ignorance here, but why is "75 ohms" the magic figure?

 

It is just the SPDIF standard.  Sony/Philips could have picked any practical impedance, like 50 ohms or something else.  But they chose 75 ohms, presumably after a whole bunch of meetings.

 

Cable impedances that are easily available are 50 and 75.

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Please excuse my ignorance here, but why is "75 ohms" the magic figure?

It is the chosen spdif  transmission line impedance and It is important for [digital] signal integrity!

 

The following is a simple read of Source/Receiver Impedance Matching/Mismatch and Signal Integrity... https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwi1qqut94_KAhVD2qYKHWqZAGwQFggbMAA&url=https%3A%2F%2Fwww.altera.com%2Fcontent%2Fdam%2Faltera-www%2Fglobal%2Fen_US%2Fpdfs%2Fliterature%2Fwp%2Fwp_sgnlntgry.pdf&usg=AFQjCNHuRbQVCB4N-D6hQISqt-5U9vGcpw&bvm=bv.110151844,d.dGY  :)

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Thanks lads, I have a little reading to get through.

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I took some measurements of an optimised SPDIF link.  

 

The first picture shows the set up.  This is from an old, but still excellent Meridian 200 transport with modified (by moi) output to a Metrum Octave DAC, again modified.  The small silver box is a Minicircuits 75 ohm power splitter so that the real time signal passing through can be picked off for display.

 

The second picture shows the picked off SPDIF signal.  This is displayed on a Tektronix 7854 scope with 7A29 plugin, and a 75 to 50 ohm impedance convertor.  I have measured the bandwidth of that combination using a tunnel diode pulser with 30ps rise time, at 740MHz  That is way overkill and shows small ripples on the waveform that are invisible at lower bandwidths.  The measured rise and fall time are equal at 1.3ns.  The signal amplitude is 60mV and is lower than the required 400mV as a result of insertion losses in the power splitter and impedance convertor.

 

post-153047-0-69148700-1451906479_thumb.

post-153047-0-29452900-1451907014_thumb.

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Can anybody point me to a single, verified blind test that proved in real terms that exotic speaker cables sounded better than standard quality speaker cables please let me know.

 

I have spent about 15 years looking. I did however come across about a hundred or so, anecdotal and verified blind tests, that disproved that listeners could tell between exotic/expensive high-end cables and bog standard ones.

 

In a few cases it is on record that on system "B" coat hanger wire was used as cables unknown to the listeners, and the listeners could not tell the difference.

 

So google "speaker blind test coat hanger wire" and see what you get. 

 

Cheers

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Can anybody point me to a single, verified blind test that proved in real terms that exotic speaker cables sounded better than standard quality speaker cables please let me know.

 

I have spent about 15 years looking. I did however come across about a hundred or so, anecdotal and verified blind tests, that disproved that listeners could tell between exotic/expensive high-end cables and bog standard ones.

 

In a few cases it is on record that on system "B" coat hanger wire was used as cables unknown to the listeners, and the listeners could not tell the difference.

 

So google "speaker blind test coat hanger wire" and see what you get. 

 

Cheers

 

Are you one of these people that need "verified" (by who?) tests before you can make a decision, Steve?

 

Why not do experiments off your own bat - based on recommendations from others - and decide as a result of them?

 

That's what I have done. ;)

 

Andy

 

 

 

Andy

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Guest Doppler Effect

Why not do experiments off your own bat

 

No.  This thread is about power cables (as well as interconnects such as those used for SPDIF).  Please do not attempt blind tests with power cables in which one is a coat hanger.  It is very silly and more than a bit dangerous.

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