clockwork247 @ Wed Jul 30, 2008 9:57 pm wrote:
MorganLeFey @ Sat Jul 19, 2008 2:04 am wrote:
It sounds very like a cable problem. the shures we bought 2nd hand came with xlr to jack cords that gave us the same problem. the home theatre system I was trying to plug in to practise with (we are talking long before I had my own pa system and was hiring one for the few gigs we got at the beginning)
A musician came one day and said it was due to the cord being either balanced or unbalanced...whichever way it went, (cant recall which it was now) he did a bit of rewiring and bingo we had a beautiful volume level.
balance and unbalance cable is real easy. most of the time you'll want balance, there's technical aspect about the differences that I won't get into (not qualify and frankly I don't understand most of it haha), but at any rate, balance cable will let you use longer cables without loosing signal quality, most microphone uses balance cable (TRS or XLR).
To bore you guys with technical details. The reason you want to use a balanced cable is that your signal degrades a lot slower with it then using a unbalanced cable. The balanced cable uses what I learned as a differential transmission. You notice that balanced has 3 connectors? Well, the third connector is the ground that shields the pair of wires used for transmission. One wire will transmit the signal as is, second wire will invert the polarity of the signal and send it down the line.
Why is this better? Simply put, better noise immunity. There are two methods of differential transmission. For digital signal, this method was used in computer interface like SCSI interfaced used on disk drives, one signal goes from 0V to 5V, other goes from 0V to -5V. So, instead of just 5V differences in signal, you get 10V difference. If you see it on a oscilloscope, you will see that the digital signal will degrade in voltage and in width as you go further due to built in resistance of the cable. So, if there is a noise that is few volts, it will not interfere with the actual digital signal or give false data because the voltage of the noise was high enough to trigger the receiver. Bottomline is less, errors and better data. This is a better method when the data is 0s and 1s that travels.
For the analog signals, like the ones that goes from mixer to powered speakers, they use the same method to transmit, inverted signal on one cable. However, the recovery is different. What they do is, when they receive the signal at the other end, they invert the signal again and match it with the original signal. If there are any differences, that is the noise and you just cancel that out from the original signal and you have a much cleaner signal. So, now you can run longer and have more interference but you can recover a cleaner original signal from the transmission.
Compare this to two wired, unbalanced signal for analog signal. One wire is grounded and ther other one sends the original signal. Since the ground is stable, whatever noise added to the original signal is still there and difficult to filter out. So, they are less likely to transmit cleaner signal over a long distance.
If you can, I would highly suggest you use a balanced cable if you can, specially if your wiring is going over a power line or near a cell phone. They will protect your signal much better from interference over any distance.
Login
Register
FAQ
Search
