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  #1  
Old 10-01-2007, 01:47 PM
toneski toneski is offline
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Default Should I Kick myself over cables. Please help!!!

Hi Everybody,
I don’t know whether I should be drowning my sorrows in a barrel of whisky right now but your advice is needed. I recently purchased a sound booth and I needed to rig up a wiring loom for microphones, instruments, headphones, etc from it to pre-amps within a rack and a mixing desk. I decided to utilise Mogami Starquad cable at great expense as the cables would need to be running past a number of power cords, VDU cables, etc to avoid any possibility of electrical interference, hum, etc. It does have slightly higher capacitance than ordinary Mogami Microphone cable and now I hear on the forum that this might reduce the quality of the signal by attenuating high frequencies. Should I rip out all the Mogami Starquad and utilise ordinary Mogami microphone cable. The length of the cables to the preamp I am using, from the Sound booth is 10metres approx, (32 feet approx) and from the sound booth to the mixing desk 12metres approx, (40 feet approx). On the Mogami website capacitance figures are:

Starquad Microphone cable W2534 97pf/metre or 29.6pf/ft – conductor to conductor.

Ordinary Mogami Microphone cable W2549 76pf/metre or 23pf/ft, conductor to conductor.

The preamp I am using at the moment is a Focusrite Red 7, the microphone generally for vocals is a SE Gemini MKII at the moment. All lines are balanced. Going on the Canare website their starquad cable has a capacitance of 150pf/metre(46pf/ft) and they have a chart showing that a 100m starquad cable starts attenuating frequencies above 20khz and then there is a slow drop off to 200khz. So are my starquad cable runs choking high frequencies and effecting my high end and should I replace them again at more expense with ordinary Mogami microphone cabe, (and at the same time give myself a good kick up the backside).

Many thanks for all your help and advice,
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  #2  
Old 10-01-2007, 02:01 PM
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JFreak JFreak is online now
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Default Re: Should I Kick myself over cables. Please help!!!

Are you seriously running over 100m cable runs? If not, do not make this too big an issue.
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Old 10-01-2007, 02:35 PM
Ragged Edge Ragged Edge is offline
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Default Re: Should I Kick myself over cables. Please help!!!

Quote:
Going on the Canare website their starquad cable has a capacitance of 150pf/metre(46pf/ft) and they have a chart showing that a 100m starquad cable starts attenuating frequencies above 20khz and then there is a slow drop off to 200khz.
I don't think there is cause for concern, your microphone will be attenuating above 20khz a hell of alot more than any loss associated with your cabling.

cheers,

ragged.
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Old 10-01-2007, 03:08 PM
toneski toneski is offline
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Default Re: Should I Kick myself over cables. Please help!!!

Maybe I'm just a born worrier JFreak and Ragged, many thanks for the replies, any other opinions?
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  #5  
Old 10-01-2007, 04:48 PM
Richard Barrie Richard Barrie is offline
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Default Re: Should I Kick myself over cables. Please help!!!

I suspect it was my post on another thread that has alarmed you.

I would never use anything other than StarQuad cabling for mic level signals especially in a potentially electrically noisy environment. In fact the longer the run the more neccessary it is to have the best possible noise rejection and it is not unknown to have several hundred meters of StarQuad mic cable (in exceptional cicumstances). A small EQ correction, if desired, is much easier than trying to hide a low level buzz.

If you want the the least noise and the best frequency response you really want your mic pre-amp as close to the mic as possible and various manufactures have excellent remote controllable mic pres but watch out for mechanically noisy transformers in power supplies.
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Old 10-01-2007, 05:25 PM
toneski toneski is offline
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Default Re: Should I Kick myself over cables. Please help!!!

Hi Richard,
Yes it was your post that got me worrying and your reply is somewhat reassuring. I was going to make up cables to go between my preamp and into my patchbay only a meter away, patchbay leads with the required trs neutrik connectors and the leads to my Coleman monitor controller and leads to my active monitors out of the Mogami Starquad cable that I have as well, is this a bad idea? Should I use something else instead. I could try your idea of moving the preamp nearer the mike which would be difficult in the sound booth as it is relatively small, (roughly 6ft by 4ft), and it has LCD monitor and computer keyboard, add to that the mike stand, etc and space begins to become tight, however it is not impossible. The balanced signal from the preamp if I did move it to the sound booth would still need to travel through the 10m approx of starquad cable to reach the 192 I/O, would that be detrimental? Or am I just being anal. If I did decide to go for preamp with a remote option as my next preamp it would really reduce choice in what I could get on a tight budget. I don't know maybe I just need some Prozac!!! Any opinions, help and advice would be appreciated with the cabling and the Prozac!!! Many thanks,
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  #7  
Old 10-01-2007, 09:56 PM
tvent tvent is offline
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Default Re: Should I Kick myself over cables. Please help!!!

I'm just chiming in here, and admittedly it has been several years since I have taken ANY serious math or electronics classes (and the seriousness of those is debatable), but doesn't capacitance effect LOW frequencies much more than high frequencies?
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Old 10-01-2007, 10:28 PM
propower propower is offline
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Default Re: Should I Kick myself over cables. Please help!!!

Hey there,

It all depends on the bandwidth you need............

1) The capacitance of the wire works into the parallel impedance of the output impedance of your microphone and the input of your mic pre. The worst case is a high output impedance microphone and high input impedance preamp. For rough figures let's use 300 ohms for the mic and 1Kohm for the preamp. Total dc resistance here would be ~230 ohms.

2) The equation for the -3dB point of a simple RC circuit is freq_3dB=1/(2*pi*R*C).

3) In your case you have 72 ft of wire at 46pf/ft ~ 3500pF.

4) The -3dB point is ~198kHz. Not too bad... If you record at 44.1 .....Not the best for 192kHz though..... AND..............

5) That is only the amplitude attenuation. The bigger problem is phase shift. The Phase shift from a simple RC pole begins a decade (power of 10) earlier. So at 20kHz in this example you are starting to get a minuscule amount of phase shift from this pole. This is still very small until you get much closer to the pole. For the simple pole the phase shift hits -45degrees at the -3dB point. The increase in phase shift is pretty gentle at first (I know I should go look up the formula but..........).

6) The graph on the Canare site tells you attenuation but doesn't explicitly say the output impeadnce of the mic and pre being used. Working backwards I see that they assume more like 180ohms. Not a bad assumption really. Most of the mics I have are more like 150ohms. Using the exercise above that would give a -3dB point of more like 350kHz.

-Lee
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  #9  
Old 10-02-2007, 01:03 AM
25ghosts 25ghosts is offline
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Default Re: Should I Kick myself over cables. Please help!!!

I have yet to hear a difference from a regular type mic cable to a top priced one. I've tried - I've tested but I can't hear the difference. If you have any insecurities then I suggest you try a short mic cable of "high quality" and compare it to the cabling you have now. Record the same source of course. What I have found to be important is to have split power circuits. i.e. one power line for light etc. and one power line for audio equipment.

However, IMO - this cabling thing is a question of philosophy. I guess the only thing that can reassure you is to do the test/comparison yourself.
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  #10  
Old 10-02-2007, 02:44 AM
Richard Barrie Richard Barrie is offline
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Default Re: Should I Kick myself over cables. Please help!!!

Toneski, I think that last couple of answers should reassure you. My personal opinion is that the biggest (theoretical) influence on the signal path is caused by having connectors of different metal types. I am a strong believer that gold should mate with gold, silver should mate with silver etc. Non similar metals in contact will form a junction where electron migration will take place.
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