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Component to Component distances and its effects on PRAT


cjf
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In the audio world, there is much talk about how the presence of a large amount of Jitter can effect SQ. Jitter of course being an issue related to timing drift from some clock reference point.

 

If you place any value on what those who measure Jitter say or what they consider is a large or unacceptable value for a Jitter measurement then I feel confident in using a value of 500ps (picoseconds) and up as being considered less then desirable. Or maybe even the starting point of being audible.

 

Anyway, with that out of the way one thing that I've been curious about lately is how my decision to place my PreAmp and Amp about 30ft apart is effecting my listening sessions. I have approx a 30ft run of XLR cable going from the back of PreAmp to my Amps. Taking into consideration the fact that there is no benefit of "buffering" involved in this analog connection I wonder how this distance is influencing what I hear coming out of my speakers in relation to the real event as it occurred at the time of the recording itself.

 

As an example, it is believed that the speed of light travels about 12" per ns (nanosecond). It is also said that the speed of propagation of an electrical current is at or near the speed of light. Without splitting hairs here, let's just go with it being as fast as the speed of light. This then would mean that a 1ft run of XLR cable would have signal delay of roughly 1ns which in turn is equivalent to 1000ps (picoseconds). Using the previous example of what some consider an undesirable/audible amount of Jitter this 1000ps number is double that value.

 

In my case, I am using a 30ft run of XLR cable which would mean that I'm dealing with a 30ns delay or in other words a 30,000ps delay in timing between the signal being sent out the XLR outputs of my PreAmp and it arriving at the Inputs of my Amplifiers.

 

So with all this in mind I begin to wonder how all these timing issues are influencing what I hear coming out of the speakers and much the PRAT of the original recording is being altered because of it.

 

As an experiment I have ordered a short run (6ft) pair of the same XLR Cables I am using today (Mogami 2549) between my PreAmp and Amps to see if I can notice any difference at all by using the shorter Cables. Unfortunately this experiment will require a days worth of work to relocate all my front end gear to the front of my listening room so it can be next to my amps while also maintaining the same power conditioning layout I use today.

 

Will see how it goes but I'll say up front that I am begggng/pleading that I don't hear a difference becuase I really don't want all that gear sitting between my speakers and the esthetics of the room will be greatly compromised as a result should it turn out to,sound better.

 

I would be interested in hearing others thoughts and experiences on this topic..Thanks

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"Jitter" is probably more of a concern in the digital domain. You are probably more concerned about "Skew" with longer cables. Using cables with low capacitance, matched length, and even better: balanced goes a long way toward mitigating cable length concerns.

 

Most importantly, a known time delay along a cable does not equate to that same amount of "jitter". Indeed Ethernet signals can go a long distance with known, measurably reasonable, but clearly measurable jitter. That's because they are differential/"balanced" and with controlled and constant and known impedance.

Custom room treatments for headphone users.

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There is no jitter issue in analog connections. I have no idea why you bring up jitter in the context of analog connections between preamp and amp. It makes no sense, just as the myth of PRAT does not. However, analog cable length can change the sound. But, I believe that is a frequency domain issue, not a timing thing as implied by PRAT.

 

I have done some experimenting with analog cable length over the years. I prefer short speaker cables, as many amp manufacturers recommend. This means longer interconnects. So, here are some snapshots of some interconnect comparisons I did.

 

Many years ago, I hoped I could move my turntable/phono preamp about 30 ft. away from my preamp. I fabricated a 30 ft. single ended interconnect from some highly regarded Belden bulk cable. I listened and it sounded terrible, about the biggest difference cause by wire I had ever heard. The highs were completely gone compared to a 6 ft. length of the same wire, which sounded quite good. I surmised that the main culprit was cable capacitance acting as a filter in the top of the audio band at that length. I avoided long interconnects for a long time as a result.

 

Years later, I was upgrading my stereo to 7.1. I wanted to use separate amps for the surround and back speakers instead of long speaker cables. In a stereo configuration, I tested some 30 ft. lengths of a few XLR interconnect cables and something seemed slightly off with the sound compared to my reference.

 

I did some more research, and I discovered a moderate cost, very low capacitance interconnect from http://www.bettercables.com: under $300 for a 30 ft. pair. Subjectively, that at 30 ft. sounded slightly but noticeably better to me than 6 ft. of the top line Cardas cable I had been using in the same preamp/amp connection. I replaced all my interconnects with it and I have not looked back in over 9 years now. I do not worry about it, because I have heard the magnitude of the difference with my own ears. And, with wires, differences are seldom of the day/night magnitude in my experience.

 

Incidentally, I have heard no evidence and no one has ever convinced me that there is an audible breakin issue with wires.

 

Good luck.

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Thanks for your replies..

 

I kind of suspected that by using "Jitter" as an example it would bring about confusion to what I am talking about. Using Jitter in my original explanation was to put some context around how very small timing differences can be blamed for making one DAC sound great and another sound not as great. In that context, if people claim to hear these picosecond differences between two DAC's then what does that mean when considering the many times larger timing/delay's involved when sending an Analog signal down a fairly long (for home use) run of balanced cable from PreAmp to Amp.

 

In regards to DAC's were talking about picoseconds but in regards to an Analog signal traveling 30ft down a cable before its amplified and doesn't have the benefit of buffering like in a DAC to make up for timing differences then it would seem somewhat reasonable to think this massive difference in time between the two examples could also be heard.

 

But with that said, I am aware that Jitter in and of itself doesn't apply to an Analog connection. As it stands now I am pretty happy with the sound of my system despite this long connection between the two components but I am also very curious to know how things would sound with a significantly shorter cable run thrown into the mix. I have no expectation that it will be night and day from what it is now but if by some small miracle it turns out to be fairly noticeable sounding then I have some decisions to make. Those being, live without the difference and maintain the more esthetically pleasing look of not having a bunch of gear sitting between my speakers or bite the bullet and move the equipment to take full advantage of the investment I made so I can hear everything it is capable of.

 

Hopefully this explanation makes more sense...Thanks

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