MEASUREMENTS: Analogue RCA Interconnects.

Now that I've measured the main digital cables used for audiophile listening these days (USB, coaxial, TosLink), I figure it's time to demonstrate what happens when we bring the testing methodology with analogue cables. [I'm hoping in time HDMI will make some headway into the audiophile DAC world since I look forward to multichannel playback one day through my computer server.]

Remember why we got digital in the first place: robust data storage free from transmission and generational losses - in other words, resistance from corruption.  By transforming data into 1's and 0's, we quantize the data into binary form and complexity is thus encoded in larger quantities and combinations of this quantized binary data which can be saved in a form which makes detection and correction of error possible.

As a result, when digital 'works', it likewise tends to be 'all or nothing'. What we saw with the digital cables is an example of this. Despite some really poor quality cables tested (the Dr. Frankenstein models!), the measurements were essentially identical in each case (they all worked). Parameters like impedance and capacitance of the cable do not affect the transfer of data unless of course they are outside of tolerance for the interface. It's of course possible that the occasional 'bit' of error occurred with poor cables, but obviously it was not large enough to encroach on the measurement results (nor affect the subjective audibility when I was listening). Beyond "bits are bits", in the timing domain, there have been reports of very long cable lengths potentially worsening timing of the digital signal (ie. jitter), what I have seen suggest lengths of 20-30m AES/EBU adding maybe 20ps - totally irrelevant to audio performance and at lengths we generally do not use in the consumer setting.

Let's see now how good ol' analogue interconnects of various lengths fare.

Here are the models being tested:

Cable A:
3' freebie RCA cable that came with an old cheap DVD that has since broken. Connectors not gold plated.

Cable B:
3' Radio Shack shielded RCA cable. Gold plated connectors.

Cable C:
6' Radio Shack shielded RCA cable. Gold plated connectors.

Cable D:
10' poorly shielded composite cable (with stereo audio). Gold plated connectors.

Cable E:
3' pure 4N silver, 4-core braided interconnect. Connectors are gold plated Neutriks. Soldered with Cardas Quad eutectic silver solder. Got this cable about 2 years back and used for my SACD player from here.

Cable F:
With apologies to Keaton & Minoeall-san, I used the 'Super Connectors' from the "Best-Coaxial-Digital" cable along with the two lengths of 10' composite cable and 6' stereo RCA and created an un-audiophile-approved 16 foot RCA "double cable" interconnect.

Setup:
Win8 laptop --> shielded USB --> CM6631A async USB to SPDIF --> 3' coaxial --> AUNE X1 DAC --> *test analogue interconnect* --> E-MU 0404USB --> shielded USB --> Win8 laptop

Summary RightMark 6.2.5 results (24/96):

Frequency Response:

Noise Level:

THD:

Stereo Crosstalk:

Summary:
1. Analogue ain't digital! Although in most ways the measurements are very similar (these are short lengths of interconnects after all), mild differences can be found.

2. Frequency response unchanged among the cables. Interesting. Some people talk about analogue cables as "tone control". I don't see it using these interconnects even with longer length (there is a hint of high frequency roll-off with the 16' cable but really this is trivial) or different conductor material. Using silver interconnects, there are no changes in the frequency response to suggest these cables sound "brighter" as some contend :-).

3. Interesting Stereo Crosstalk performance. Stereo crosstalk looks to be sensitive to cable length. The silver cable had the least crosstalk up to 5kHz and then increased from there - this is possibly a function of the fact that it's constructed as 2 separate cables as pictured above rather than the zip-cord arrangement of the other cables.

4. Measures like THD should not (and in fact does not) show a difference. After all, cables are passive "components" so should not introduce harmonics into the equation. As for noise floor, I suspect if I were to test under conditions with strong RF noise the poorly shielded cables would perform worse (may try this later), but in the home environment where I tested, obviously this was not a problem even in reasonably close proximity to the laptop, DAC, and E-MU ADC.

There you go. Analogue interconnects do make a slight difference and this is quite measurable particularly in terms of stereo crosstalk performance. Remember that these interconnects are of relatively short lengths so minor differences are really not surprising. The obvious question is - would humans be able to differentiate these interconnect cables based on listening tests? I honestly doubt it. Subjective listening using my test setup did not reveal any noticeable change with the long cable vs. the short silver cable. Realize that even with the long 16' cable, stereo crosstalk was still below -75dB which should be inaudible - for comparison, high-end LP cartridges are only capable of 30-40dB crosstalk performance.

Musical selection tonight was Rachel Podger & Brecon Baroque's renditions of Bach's Violin Concertos on Channel Classics (SACD converted to 24/88). Sounds great with the 16' Frankenstein cable with my Sennheiser HD800 headphones off the E-MU 0404USB.