Allen & Heath AP5195 用户手册

PA User Guide 

17 

 

   Adjusts the stereo position of the channel 

signal  in  the  main  LR  mix.    At  the  centre  position 
equal signal is sent to the L and R outputs.  Fully 
anticlockwise all the signal routes to L and none to 
R, and fully clockwise the reverse is true.  The 
control has a 3dB attenuation at its centre position.  
This ensures equal power as the sound is panned 
from one side through the centre to the other side.  It 
also has a mechanical detent to help you find its 
default centre position quickly. 

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  Using PAN   If you are working with a stereo PA 

system use PAN to set the position of each signal in 
the  mix.    In  live  sound  mixing  it  is  best  to  set  pan 
centre or close to centre for most signals so that all 
listeners hear a similar balance regardless of their 
position  in  the  room.    Sounds  such  as  kick  drum, 
bass and lead vocal would usually be set centre.  
Ambient or backing sources may be panned slightly 
to spread the image.  Stereo sources such as 
backing tracks, keyboards and sound effects may 
be panned fully or use the stereo channels instead.  
If you are working with a mono PA system simply set 
all pan controls centre. 

 

   Press this switch to turn the channel 

signal off.  The large red LED lights to warn that the 
channel is muted.  Mute affects the channel pre and 
post-fade sends.  This ensures that the feeds to the 
foldback monitors, effects, aux and house mix are 
turned off when the channel is muted.  It does not 
affect PFL.  You can still use PFL to check the signal 
while the channel is muted. 

 To avoid loud clicks or unexpected noises 

 

      Press  this  switch  to  listen  to  the  channel 

signal in the headphones and display its level on the 
main meters.  This lets you check each channel 
signal independently without affecting the outputs.  
PFL is sourced pre-fader, pre-mute.  Pressing PFL 
automatically overrides LR or 2TRK in the 
headphones.  The channel PFL switch LED and the 
big PFL/AFL indicator below the main meters light to 
warn that PFL has been selected. 

PFL  stands for Pre-Fade Listen.  It sends the 

signal taken just before the channel mute switch and 
fader to the engineers personal headphones monitor 
and console meters.  This means that you can check 
the signal while the channel is muted or its fader 
down.  Note that AFL, as found on the FB1 and FB2 
masters stands for after-fade listen. 

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    Using PFL      Use  PFL  to  check  sound  quality 

and the channel gain setting when plugging in 
different sources or when you suspect a change or 
problem with a particular signal.  During sound 
check start with the channel muted.  This lets you 
set up the signal before you introduce it into the 
monitors and house mix.  Press PFL.  You should 
hear the signal in your headphones and see its level 
displayed on the console meters.  Adjust the gain 
control so that the meters read an average ‘0’ with 
loudest peaks no more than ‘+6’. 

   The PFL switch LED also provides a channel 

signal peak indication.  The indicator lights brightly 
when the pre-fade signal reaches +16dBu.  This 
means that it lights 5dB before clipping to give you 
the chance to reduce the signal before you hear any 
distortion.  If the PK! Indicator flashes turn back the 
channel gain control until it stops. 

 

      A  100mm  smooth  travel  fader  adjusts 

the signal level feeding the main LR mix, AUX and 
FX sends.  It provides up to +10dB boost above its 
normal unity gain ‘0’ position, and shuts off fully 
when pulled back to its bottom position. 

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  Using the faders   These are your main mixing 

controls.  Use the channel faders to adjust the level 
of each signal in the mix.  Normal operating position 
for dominant sounds is around the ‘0’ mark, with the 
quieter backing sounds typically in the range ‘0’ to ‘-
20’.  The +10dB boost is there to give you a bit extra 
when you need it.  If you find your normal setting is 
near maximum fader position or well below ‘0’ then 
use PFL to check that the gain is correctly set. 

The fader scale  is graduated in dB (decibel) 

markings.  The dB is a measurement of gain.  It 
relates the fader output level to its input level.  If the 
output is the same as the input then the gain is 0dB.  
That is why the fader is marked ‘0’ at its normal 
operating position, the point at which all the channel 
signal is fed to the mix.  If the fader is moved above 
‘0’ it produces more output and therefore has gain 
boosting the signal level up to a maximum of 
+10dB.  As the fader moves below ‘0’ it produces 
less output than its input and therefore has 
attenuation.  The -5, -10, -20 and -30dB attenuation 
positions are marked.  The infinity mark at the 
bottom position represents maximum attenuation, in 
other words the signal is turned off. 

The dB explained  Because of the way the 

human ear responds to sound, the decibel uses a 
logarithmic rather than linear scale.  Regarding 
audio voltages,   dB = 20log(Vout/Vin) where Vout is 
the output level expressed as a voltage, Vin the input 
level.  You can see that 0dB is the result when the 
Vout is the same as Vin.  This is also referred to as 
‘unity gain’, or gain of 1x.  For rule of thumb, gain is: 

+10dB   =   3x   at fader top 
+6dB     = 

 2x 

0dB        =   1x  (unity) 
-6dB       =   0.5x 
-10dB     =   0.3x 
-20dB     = 

 0.1x 

-30dB     =   0.03x 
-90dB     =   0.00003x   at fader bottom 

The above shows how wide the fader control range 
is.  At maximum position the signal is amplified three 
times.  At minimum position it is just 1/30000 of the 
original, effectively off. 

   Use the white block for 

labelling the channel using chinagraph marker, felt 
pen, adhesive label or tape, or magnetic label strips.  
Avoid leaving sticky residue.  Do not use chemicals 
or solvents to clean the blocks.