23
1 = Ground/Screen
2
1
3
2 = Hot (+ ve)
3 = Cold (- ve)
3-pin XLR Male Plug
(
seen from soldering side)
Generally, you will have to trust your ears to detect digital distortion as the way input meters work on
different processors depends on the way they are calibrated.
If you detect distortion, but the Stereo Efx Return PFL is showing no more than 0 dB, the problem lies
with the Aux Send circuit or the Efx Processor. If you PFL the Aux Send and all is well, then lower the
input level control on the external Efx Processor Unit and increase the Efx Return slider (S 16) setting.
☞
Most distortion problems in the Aux Send - Efx - Efx Return loop can be attributed to the input gain
setting of the actual Effects Processor (too low). The same goes for high noise levels in this loop when
the Processor input gain setting is too low, creating an unfavourable signal -to -noise ratio.
Generally speaking, all input levels should be as high as possible without creating distortion.
Remember the noise from an effects unit is always about the same level, so the more signal you apply
to it, the better the signal -to -noise ratio will be.
☞
The performance of particularly noisy Efx units or synthesizers can be greatly improved by the use of
an external Noise Reduction Processor such as the ETEK OPTIMA Digital Rack Module in the Efx
loop.
☞
Always drive these analogue recorders pretty hard as well, because the dynamic range without noise
reduction is liable to be up to 30 dB lower than the other units in the recording set up.
When recording to analogue tape recorders, also always remember to record with as bright a sound
as possible; you can always correct this on mix back. It is much worse when you find you have to
brighten up a 'muddy sounding' tape recording and in doing so, increase the noise as well. This
problem does not normally exist when working with digital tapes or HD Recorders as the dynamic
range is much higher, but remember not to create distortion.
The levels of each channel should always be at about 0 dB when recording (or mixing), if they are
gradually moving up or down the channel LEVEL sliders ( S 3) should be adjusted accordingly.
10.3 (UN) BALANCED LINE CONNECTIONS
Why are balanced line connections used? Even though all audio signal
cables (except speaker cables) have earthed screening, the shielding is
never perfect. The balanced line system is an effective way to overcome
the deficiences in the screening. Instead of using one insulated audio
conductor, two are used. These are usually twisted together and inside a
single screen. One of these conductors, wired to pin 2 of an XLR type
connector according to international normatives carries a signal called
the 'hot' or '+' signal. Pin 3 is wired to the 'cold' or '-' conductor and the
screen is connected to pin 1.
What does all this this mean? Let's consider an unbalanced line. You have one 'hot' or 'positive'
conductor, and an earthed screen. The 'hot' wire's waveform, if looked at on an oscilloscope, shows the
Audio Signal waveform. If you looked closely at the trace, random noise will be seen along the X axis.
What you don't see is the appearance of any 50 or 100 Hz frequencies, corresponding to mains hum
interference, since these frequencies are hidden in the audio signal. An AC mains frequency and its
harmonics can be picked up by any wire, and some will always leak through a cable screen. When does it
become audible?
Well, all else being equal, the amount of mains hum picked up by a cable is independent of the signal
level. Speaker signals run at 50 volts or more, enough to reduce the effect of mains radiation to a
minimum even when unscreened. At these levels another factor becomes decisive: capacitive resistance.
You should not use screened cable to wire an amplifier to a speaker and however they should be as thick
and short as is practicable. Unbalanced line level signals can normally be used over short or moderate
distances (rack to mixer etc.), but not from the back of a theatre to the stage, always provided that there
are no earth loops.
