GuitarMasterClass Blog

A pretty dull subject this, but also quite important - this is where we discuss cables and what we do with them. I initially expected this to be more complex than it was, but owing to the relocation of the vocal booth it has turned out to be pretty simple.

Lets start with a word on Audio cables. With the vocal booth sited on the opposite side of the room as was originally intended, I had the problem of sending Audio data both ways; from the microphone to the interface input, and from the monitor output to headphones for the vocalist. This is a very common problem to solve both in studios, and in a slightly different form on stage as well, and the well established and not too surprising solution is to use a stage box or snake. This is a pretty simple concept - you make a box with all your ins and outs on it, say 4 Mic Inputs and maybe a couple of Headphone sockets, wire them up and feed one thick cable out of it. The thick cable runs the distance required, and terminates in a bunch of plugs appropriate for plugging in to your interface inputs and outputs. Simple but elegant - you only have to run one cable the distance, and at the business end you have a neat mounting for all the sockets.

Snakes can be expensive of course, but I found a fairly modestly priced one made by Hosa, containing 6 XLR sockets and 2 TRS sockets (more abut XLR and TRS soon). The TRS are useful because they can be used to either run headphone outputs to the vocalist, or route stereo signals back to the mixer if that is ever necessary.

The version I got had a 50′ cable and cost just over $100. The plan was to route this up the back wall and above the suspended ceiling and down inside the vocal booth, and indeed I did that - it worked really well until I decided to move the booth! Now I have less of need for this with the new vocal booth location, but it is still a nice way of routing the cables and avoiding cable runs across the floor - I will route it along the side wall and behind the desk when it is built to keep the cabling nice and tidy.

A Digression : XLR, TRS, Balanced, Unbalanced - if the previous phrase sounds incomprehensible to you then you need to read this section before you wire a studio up! Knowing the difference between balanced and unbalanced cables can be important.

Regular, unbalanced cables are more common in lower end gear, and consist of 2 conductors, a signal and a screen. For instance, guitar cables are regular unbalanced cables. Balanced cables on the other hand consist of 3 conductors - hot, cold and screen. I don’t want to go into details here, but suffice it to say that balanced cables have much better noise and hum rejection characteristics and can run for much greater distances without degradation in quality for this reason. Higher end gear often uses exclusively balanced cabling; semi pro and project gear will often have the option of both.

In general, you should always try and use balanced connections wherever possible.

TRS and XLR are two different types of connectors used for audio connections. XLRs are most often used for Microphone connections and are always balanced. They are also used for higher end audio connections between gear when signals are low power (e.g. before amplification) and where noise is a concern - as it pretty much always is before amplification. An XLR plug looks like this:

You can clearly see the three connections there.

By contrast, a TRS connector, whilst it still has three connections looks a lot more like a regular guitar jack. TRS actually stands for Tip Ring Sleeve - the three connections you can see here:

Now, with TRS things start to get a little complicated so bear with me. TRS plugs are often used as balanced connectors in studios, but not always. They are also used as effect send and receive cables. When used in this way, they are carrying two separate signals, the pre-effect signal and the post-effect signal - the ground remains common to both signals. This allows effect inserts to be wired up with a single cable rather than two and is popular for this reason as it reduces clutter in mixing desks. A third use for TRS cables is to route stereo signals such as headphones, so be careful not to confuse the various different uses.

An additional complication with TRS plugs is that the plugs themselves are pretty similar to regular jack plugs, and the sockets are actually indistinguishable from the outside which leads to endless confusion. This is what they look like side by side:

As you can see, they look similar, both sharing the 1 (Sleeve) and 3 (Tip) conductors. The TRS though has an additional sleeve (2) and the insulating rings (4) differ between the two.

In practice, this means that confusion often reigns in amateur studios. One problem is that you can’t tell the difference between a balanced and unbalanced input socket (the plugs, yes, but not the sockets), you need to know, or it has to be marked, wheras with XLR it is very clear cut. This means that in practice, inexperienced technicians (that’s you and me!) often plug an unbalanced cable into a balanced input. This will actually work ok, since it is designed this way, but you are losing out this way on some noise rejection, especially if you hook 2 pieces of equipment together with an unbalanced cable when the equipment actually has balanced inputs and outputs. So, know your equipment and understand the difference between balanced and unbalanced.

Another common mistake is in trying to connect a microphone to a jack input. There are a couple of problems here. The first instinct is to run out an buy a an XLR to jack cable and indeed these are easily available but this is bad on 2 counts:

1. You should be hooking any microphone up to a microphone amplifier, not a line level input. Mic amps pretty much always have XLR inputs - if you don’t have an XLR input you probably don’t have a microphone amp and the results will not be good.
2. Those XLR to Jack cables usually terminate in a regular unbalanced jack - you have just lost the benefit of the balanced output of your microphone.

So think this through before you run out and buy that XLR to Jack cable - if you think you need that cable, it’s more likely that you actually need a microphone amp for best results.

Back to the subject at hand - my setup has grown organically over the last few years, and at least at the beginning I didn’t fully understand the importance of balanced cables and the subtleties of TRS. I decided to put this right and went through my setup. I was pleased to see that all my gear had balanced ins and outs so I bought the appropriate cables to make sure all the cable runs were balanced - notably from my soundcard to my mixer, and from the mixer to my new Adam monitors.

Next up is Power Cabling. Ok, not too much to say here except that I try to keep computer and audio power separate if possible, and wire things up in a star configuration as far as possible. That means pulling all power from a single point and coming out to distribution strips as far as possible - this is a good way to avoid Earth Loops. Earth loops are bad news in studio construction and can cause bad hum problems that are very difficult to trace. Sourcing all the power form a single point where practical helps to avoid this. I have had some thoughts about adding a power conditioner at least to the audio power side - this would help to filter the power and remove any spikes. I don’t have a problem here that I am aware of but I will probably add one in the future.

And finally, a word on data cabling. Again, not too much to say here - I have the usual monitor cable, the rest is pretty much USB. I have a single USB hub and will make stringent efforts to separate the USB and audio cabling as much as possible. With a built in interface as I have, unfortunately the audio cables are forced to come in and out of the back of the computer, although they are balanced. If I had a firewire or USB interface, I could move them further away, and this is one of my longer term plans. At the moment I do get some residual electronic fuzz through the monitors occasionally, and my USB disc drive is particularly bad. When the studio goes in I will be making efforts to troubleshoot this and get things as quiet as possible!

This entry was posted on Tuesday, June 3rd, 2008 at 1:08 pm and is filed under A Studio is Born. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.