Mogami vs Canare & general questions.

  • Thread starter Thread starter Slackmaster2K
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Wow thanks RE! I do have one more question though...

You mentioned quad cable not being "technically" good over 12'. Does that apply to both mic and line runs? This quad stuff seems to be the "top of the line" cable, according to say Canare's website, but it would suck if I was limited to 12' cables! I definately need 25' cables at the least. Should I use two conductor mic cable for everything?

Thanks!

Slackmaster 2000
 
Good post- just one or two points to think about...

The high capacitance of the quad cables (especially the miniature console quads) is much less of an issue for balanced line-level use than those other folks claim: I think that that 12 foot rule is *far* too conservative a number. After all, with line driver impedances down in the tens of ohms, you'd need a pretty huge amount of cable at 50pF/ft to get a measurable rolloff in the audio band. You *might* see some measurable phase-shift issues up near 500 feet, but using it for 50-100 foot line-level balanced runs should not pose a problem, to my way of thinking. Shoot, even mic-level signals can run up to about 1000 feet in well installed shielded pair...

Don't get me wrong: of course, you want to keep all cable runs as short as possible, and there's probably some gear with disastrously bad line drivers that would prove to be exceptions. But using 12 feet as the limit for line level signals is overconstraining the problem. I've seldom seen a studio where the run from board to rack was less than 30 wire feet! Don't lose sleep over that.

I personally don't use quad for line level runs simply because of the expense. Quad's forte is in the super-low-level world of microphone interconnect, simply because it has measurably superior noise immunity: that's inherent in the quad design, and is not just marketing fluff. However, the bang for the buck isn't necessarily there in line level use: that 40-50dB difference in relative levels make the quad's additional noise immunity pretty well moot when used at line level. Noise that's -70dB relative to a mic-level signal would be at -120dB with respect to a line level signal (ignoring the source impedance for the moment). *Way* down in the noise... That's why I use foil shielded pair for permanent line-level install stuff. But your mileage may vary! Using quad at line level will not _hurt_ anything- it's just not the best cost/value tradeoff, in my opinion. Of course, I may well be eating crow in 5 years, when the state of the art improves further, and I have to rip out all my fixed interconnect to keep up. (;-)

What you really _don't_ want to do is to use the quad stuff for high-impedance use, like guitar cables. 50pF/ft is *far* too high a capacitance, and the loading will _kill_ the HF response of an instrument with even relatively short cables. A 25' guitar cable made with Mogami miniature quad would not be a good match for your Telecaster, unless you want it to sound more like a Gibson EBO with tape-wound strings. (;-)

I started out very skeptical about quad mic cable, because I started my career in the pre-quad days. But after doing my own testing, and being completely skeptical: I definitely can hear the difference between good quad and good two-conductor in microphone use, especially in high-EMI areas (like live recording on a stage with theatrical dimmers right in the wings!). The noise floor tells the tale. It is nontrivial, and it is very worthwhile for critical recording. And I agree fully that improving the noise floor at every step of the process is critical in getting the best results! I just can't hear the difference between different flavors of quad.

On your noise thing in number 3: if these are line-level TRS cables, consider making a quiet bay. Get a little sheet metal, drill 5 or 6 3/8" holes in it, install 5 or 6 Neutik TRS jacks (get the plastic ones that isolate the jack mounting nut from the sleeve to prevent any possible ground loop wierdies), and solder them up so that tip and ring are connected to sleeve with say 100ohm resistors. Viola': no more noise when cables are parked in it. If you're sure that you'll never accidentally plug a line _out_ into your quiet bay, just short them. But using the resistors will make it accident-proof...
 
RE, where did you get that 12' figure? That seems suspect to me. One usually doesn't have to worry about capacitance/high end roll off until you get in to the hundreds and hundreds of feet.
 
Well

On Mogami Cable's "fill in the numbers" chart, their quad is "technically" suppose to start loosing high-frequencies above 20kHz with a run of 25' and not too much of phase shift. With Canare's quad numbers plugged-in, it's "technically" suppose to be pretty down at about 17 or 18kHz and off phase pretty badly with a 25' run. It's been awhile since I've punched the numbers in, but that's roughly right I think, if I remember correctly.

Anyhow, as I said before, oddly enough, with the "technically" bad Canare quad on paper, for some reason, I find PLENTY of high-end even from 40-50 foot microphone runs (though only 25 feet is more typical for me)! And you're more than likely going to find phase problems elsewhere than from cable. Peasonally, I'm more worried about EMI and RFI than those "technical" problems that seem only to be a problem on paper (at least for me). And that's the reason for using quad! Plus, it makes me feel more "comfortable"; which is good enough for me, if nothing else!
 
That 12 Foot "Rule"

I've been hearing that "rule" all over the place for a few years now... But as I've been saying, I've NEVER had ANY problems with it, so I don't know what THAT'S all about... Besides Canare Quad looking "bad", technically on paper as compared to Mogami Quad; and especially Mogami 2-conductor...
 
That blows my mind. There's got to be some slipped decimal places in their tables, then, or they were done with 1Kohm source impedances, or something else that's way out in left field. I'll have to go do a search on that and see those tables... I'm with you, sir: I've been doing this for years, and I just flat don't believe that 12 foot limitation.

I mean, think about it. The stuff has a nominal impedance of on the order of 40 ohms: where are they getting all that loss from? Let's do a (very!) rough approximation, just for grins. The -3dB point (Ft) is at 1/(2piRC). With a source impedance of 100 ohms (guessing pretty high for pro equipment, just for argument), and spec'ing a -3dB point of 75kHz (so we'd be less than 1/2dB down at 20kHz, just for argument, with a first order lowpass)- solving for C, that's 1/75000*100*2*pi, or 2.122e-8 Farad. At 50e-12 Farad/ft, that's 424 feet! A lot different than 12...

I don't get it. But if the manufacturers are saying it somewhere, I'll pay attention- at least until I know what their assumptions were. Got any URLs for those tables?

I'm not trying to argue with you- I just hate to see people overconstrain their designs, and 12 feet is _way_ overconstrained. Like you, I've used 50 foot runs for years, and have always done so based on knowing that I wasn't doing any harm...
 
I just found the Mogami cable calculator, over at http://www.mogami.com/e/cad/mic-cable.html

Now, using the 2799 miniature console quad I have (pretty lossy stuff), and a source impedance of 100ohms and a load of 600 ohms, I get dead flat response out to 50kHz and less than 5 degrees of phase shift at 50 _meters_, or approximately 170 feet.

To get my 1/2dB of loss at 20kHz, I has to crank the length up to 150 meters: pretty much right where my much simplified 1/(2piRC) model would put it. And even so, the phase shift at 20kHz is less than 10deg. All's right with the world...

I wonder if that "12 foot" rule came from someone who decided that the only acceptable performance was zero attenuation and zero phase shift, and interpreted meters as feet? Talk about overconstraining a design: I don't think that group-delay-created phase shifts are audible in the 15-20kHz range, until you get pretty big: maybe 30deg.

Whew: you guys had me worried for a while- I was scared that the audiophiles had all got together and revoked Ohm's Law, or something. (;-) Anyway, I still believe you can do line-level runs up to 100 feet in perfect health, with negligible losses, with either pair or quad. You can go further with pair, if you need to, but either will do inside your room!
 
Ok then!

One quick question: how delicate is the foil sheilded stuff? Should it just plain never be moved? What are the noticable effects of the foil wearing out or even breaking? (like interference obviously....but how will it become apparent...just curious)

Slackmaster 2000
 
It's not that delicate: it'll take a fair amount of moving around. If you use it on the back of your patchbays, it'll probably last for several *hundred* install/remove/reconfigure cycles. It's just not robust enough for mobile use, like running direct to mic stands. It's also much stiffer, and has more of a "memory" effect: it wants to stay coiled like it was from the factory, until you ty-rap it into bundles. It'd be a pain in the ass to deal with as individual runs- but it's great in big set-and-forget bundles.

The failure mode is a gradual increase in the noise floor, as the effective shielding percentage drops off (the busted-up foil becomes less effective, but the drain wire keeps shield continuity going). You'll also see a major increase in triboelectric noise (handling noise, or crunchies when the cable is flexed). The foil shielded stuff is pretty bad in the handling noise department even when brandy-new- but once again, in line-level applications, that's much less of an issue than with mic levels.

Have you ever used a really _old_ mic snake, working live? Say, on its 100th show? Snakes are almost all foil-shielded, just to make the resulting cable smaller and lighter. They do wear out: you get low-level crunchies when you move them, and the whip ends at the board will eventually go intermittent. But even so: snakes can last for hundreds of shows, if treated kindly...
 
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What He Said

Well I can't follow skippy with the math (actually I could with this, but it'd take me A LOT longer to figure-out than it's worth right now), but everything he's said seems correct! As I said, it's been quite a while since I've even looked for that chart (Maybe almost 2 years?), so I don't recall what the exact numbers were, but yeah, I wouldn't be surprised if it was some audiophiles hanging around the recording sites and it finally got passed as the "12 foot rule" for quad cable for a few years; as I have heard that for quite a few years!
 
Ok guys, thanks a lot!

I'm going to use Canare Star Quad for everything...both the mic & fixed install variations.

Also, I like skippy's idea for a quiet bay. Yes the cables in question will be 1/4" TRS. However, I might just eventually break down & buy a patch bay if I'm going to go through the effort.

Slackmaster 2000
 
Audiophiles say the funniest things, sometimes. Can't live with 'em, can't shoot 'em. But you already knew how I feel about those guys.... (;-)

Seriously, though: for an amusing exercise, get an Amber or the equivalent and look at the phase shifts/group delays through some of the most revered outboard gear and preamps, or through most of our boards. Compared to some of that, the 5-10deg shifts we get from one hundred feet of the _cable_ is pretty trivial. I remember that the phase shift with my old analog tape deck neared 60deg at 18kHz, record-to-repro, and I was real proud of that at the time.

But now we regard all that as part of the *vintage sound*, and desirable. Make my head spin! Good? Bad? Who knows? I just want to find the "suck" knob and turn it all the way down...

I still absolutely agree that keeping cables short is a win: everything should be as short as possible, but no shorter. (;-) Anyway, I think we can all sleep better at night...
 
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