Cable differences are real

[mansr]

8 minutes ago, d_elm said:

Could it be for 10MHz square waves for clock signals ?

Such signals should use properly impedance matched connections.

[Jud]

42 minutes ago, mansr said:

Because that's where the differences are.

 

Yeah, wondering about any possible effects of those differences.  Is the dip in the AQ response, for example (1) completely insignificant for audio, (2) at a frequency range where there are common sources of interference and thus possibly beneficial, or (3) the result of an intentional design decision in shielding, dielectric, material, etc., thought to be otherwise beneficial or neutral in the audio range?

[Arpiben]

As a reminder:

* 16/44.1 kHz -> 1.4 Mbps/1.4MHz

* 24/768  kHz -> 37 Mbps/37MHz

* 30 years ago RG58 cables were already carrying 140Mbps data (HDB3) over lengths up to 100 meters or more.Obviously when needed root square frequency correction was applied.

[mansr]

1 minute ago, Jud said:

Yeah, wondering about any possible effects of those differences.  Is the dip in the AQ response, for example (1) completely insignificant for audio, (2) at a frequency range where there are common sources of interference and thus possibly beneficial, or (3) the result of an intentional design decision in shielding, dielectric, material, etc., thought to be otherwise beneficial or neutral in the audio range?

1. It's at approximately 48 MHz, so entirely irrelevant for audio.

2. I have never heard of any particular problems near 48 MHz. Besides, the location of the dip (probably) depends on the length of the cable.

3. It is obviously somehow a result of the cable construction. Why they thought plain coax wasn't good enough is anyone's guess.

[Arpiben]

18 minutes ago, Jud said:

 

Yeah, wondering about any possible effects of those differences.  Is the dip in the AQ response, for example (1) completely insignificant for audio, (2) at a frequency range where there are common sources of interference and thus possibly beneficial, or (3) the result of an intentional design decision in shielding, dielectric, material, etc., thought to be otherwise beneficial or neutral in the audio range?

 

The dip was around 47MHz -> Insignificant at audio/digital audio rates.

 

[Hugo9000]

Leaving aside relevance of a known phenomenon to audio frequencies:

 

For those audiophile cable companies that claim skin effect is an important consideration, do their products actually provide anything useful at the frequencies where skin effect is relevant, versus a conventional professionally engineered cable for such applications?

 

For those audiophile cable companies that claim triboelectric effect is important, is there anything in their product that is useful versus a conventional professionally engineered cable for applications where triboelectric effect is actually relevant?

 

And so on for the various scientific or pseudoscientific reasons why the audiophile cable companies say we should choose their products over another.  Do they address the scientific phenomenon at all in the geometry/materials/techniques?  Or is it simply "double bullshit" (not relevant to audio AND not even addressed effectively or at all).

 

[Allan F]

On 1/7/2019 at 1:39 PM, mansr said:

The best part about that zip cord is that I ordered 10 m. After using some of it, there's still 13 m left.

 

Is this your way of saying that less is more?

[mevdinc]

See what @mansr and others make of  the article below.

http://audiofi.net/2019/01/audio-engineer-claims-his-null-tester-settles-the-debate-on-wires/
 

[Jud]

2 hours ago, mansr said:

1. It's at approximately 48 MHz, so entirely irrelevant for audio.

2. I have never heard of any particular problems near 48 MHz. Besides, the location of the dip (probably) depends on the length of the cable.

3. It is obviously somehow a result of the cable construction. Why they thought plain coax wasn't good enough is anyone's guess.

 

Thanks.  Any way to hook up these cables in the same spot in your system and measure whether there is any difference in signal/noise at the speaker terminals?

[Jud]

2 hours ago, Arpiben said:

As a reminder:

* 16/44.1 kHz -> 1.4 Mbps/1.4MHz

* 24/768  kHz -> 37 Mbps/37MHz

* 30 years ago RG58 cables were already carrying 140Mbps data (HDB3) over lengths up to 100 meters or more.Obviously when needed root square frequency correction was applied.

 

Yes, I was thinking more of their use as analog cables, but for digital the frequencies would be much higher.

[mansr]

59 minutes ago, mevdinc said:

See what @mansr and others make of  the article below.

http://audiofi.net/2019/01/audio-engineer-claims-his-null-tester-settles-the-debate-on-wires/

I agree with Ethan Winer.

[mansr]

Let's look a bit more closely at reflections. One way to observe them is by sending pulses into one end of a cable, leaving the other end unconnected, and measuring what comes back. To this end, I have configured the AFG to generate 6 ns pulses. The AFG output is connected via a short RG-58 cable and a T coupling to the scope input (1 MΩ) and the cable under test. We start with a 2-metre RG-58.

 

The first pulse seen here is the feed from the AFG. The second is the reflection from the open end of the cable. Since the round-trip distance is 4 m and the signal takes about 5 ns/m, the delay is 20 ns.

 

If the far end of the cable is shorted instead, the reflected pulse switches polarity:

 

Terminating the cable with a matched 50 Ω load, the reflection pretty much vanishes:

 

A 75 Ω termination causes a small positive reflection:

 

In general, the reflection is positive if the terminating impedance is larger than the characteristic impedance of the cable, negative if it is smaller.

 

With a 4 m RG-59 cable, we get multiple reflections:

 

The reason for this is that the cable from the AFG has a characteristic impedance of 50 Ω while the RG-59 is 75 Ω. This causes the first reflection (the second pulse in the scope image) to be reflected down the cable with flipped polarity, then once more at the open end (preserving polarity) before we see it 80 ns after the initial pulse. This repeats to produce a small positive pulse at 120 ns, and so on, each time attenuated a bit more. The closer the two impedances, the smaller the reflection will be. At the extremes of open or short circuit, all energy is reflected.

[Ralf11]

anyone surprised that the true audio cable is one of the worst??

[semente]

20 minutes ago, Ralf11 said:

anyone surprised that the true audio cable is one of the worst??

 

Worse can be euphonic?

[mansr]

Just now, semente said:

Worse can be euphonic?

Only if it makes an audible difference.

[semente]

11 minutes ago, mansr said:

Only if it makes an audible difference.

 

Noise-shaping and a wide-bandwidth amplifier?

[Arpiben]

Just by curiosity did you measure both directions of AQ  'pseudo' directional  RCA cable ? 

Not defending AQ,but analogue RCA cables are not supposed to work at Mega Hertz frequencies or have same bandwidth as coaxial ones.

[mansr]

Time for another demo. This time we're using the 4 m RG-59 between the noise generator and the spectrum analyser. Remember, the impedance of both of these is 50 Ω. With the 75 Ω cable we will thus get a small reverse-polarity reflection in either end of the cable. If cable round-trip is an odd number of half wavelengths long (0.5λ, 1.5λ, etc), the reflections will be 180° out of phase with main signal and partially cancel it out. The cable is 4 m long, so the round trip is 8 m which is half a wavelength at 12.5 MHz with a signal speed of 5 ns/m.

 

 

As expected, there is a dip in the spectrum at 12.5 MHz and every 25 MHz above.

[mansr]

1 minute ago, Arpiben said:

Just by curiosity did you measure both directions of AQ  'pseudo' directional  RCA cable ?

We'll get there in a bit.

 

1 minute ago, Arpiben said:

Not defending AQ,but analogue RCA cables are not supposed to work at Mega Hertz frequencies or have same bandwidth has coaxial.

They don't need to work at high frequencies, yet most of them do.

[mansr]

Now that we've familiarised ourselves with the cable impedances and signal reflections, we are ready to take on the AudioQuest cable. We begin by sending pulses into the cable with far end open, observing "correct" orientation according to the arrows.

 

 

What the hell? That's not how it's supposed to look. The first reflection is strongly attenuated, and then the second one is stronger again. Clearly, this is no normal cable. Turning it around, feeding it in the "reverse" direction yields this result:

 

Well, that's more like what we expected, a strong first reflection after about 10 ns followed by some minor wiggle. Apparently there is something asymmetrical about this cable. The only way to find out more is to crack open the connectors. Doing so reveals two insulated conductors connected to the pin and sleeve of each plug. Additionally, a shield is connected to the sleeve at the "output" end of the cable only. My guess is that the dangling shield causes additional signal reflections not seen with a properly constructed cable. In the reverse configuration, the shield and the main conductors are open in the same end, giving it a more normal behaviour.

 

Configuring a second scope channel to 50 Ω termination (same as the spectrum analyser) and connect the other end of the cable there, we obtain this image:

 

We note that the propagation delay of the pulse is 6 ns. The signal speed is apparently a bit slower in this cable than is usual. Furthermore, the received pulse amplitude is much lower than that at the source end, the "missing" energy having been reflected back. Indeed, 6 ns later, a negative pulse shows up at the input, and then a positive pulse at the output after another 6 ns.

 

For comparison, the same measurement of a 2 m RG-59:

 

Apart from the longer delays due to the extra cable length, the reflections are much smaller than with the AQ cable. From this we can conclude that the characteristic impedance of the latter is higher than 75 Ω.

 

A longer cable would have been preferable for this test as that would have provided better separation between the various pulses. However, this is what I had (didn't pay for it), and I'm not curious enough to buy another one.

[d_elm]

@mansr, it would be interesting if you could measure some popular configurations of the Lush^2 USB cable.

[mansr]

16 minutes ago, d_elm said:

@mansr, it would be interesting if you could measure some popular configurations of the Lush^2 USB cable.

That would be even more pointless than this exercise.

[pkane2001]

26 minutes ago, d_elm said:

@mansr, it would be interesting if you could measure some popular configurations of the Lush^2 USB cable.

 

Stand by. Going to do some of this in the near future, but without the fancy measuring equipment that Mans uses 

 

[d_elm]

42 minutes ago, mansr said:

That would be even more pointless than this exercise.

What do you mean ?  

[mansr]

9 hours ago, d_elm said:

What do you mean ?  

Measuring analogue audio cables in the 100 MHz range is already rather ridiculous. A USB cable either works or it doesn't, no matter what characteristics it possesses.