Allen&Heath 21 Series - Manual (Page 13)

10
1)
2)
The audio amplifier system noise is allowed to be greater
than the ambient (background) noise of the original sound.
Details of the quieter sections of programme are lost.
The audio amplifier system maximum signal level for
faithful reproduction is exceeded by the original sound.
Details of the louder sections of the programme are lost
and the audio system adds masking distortions generated by
Make
overload of the amplifiers.
some simple tests:
Set up a mic and get someone to play the piano in the studio,
set the mic in close to the piano.
Select PFL on the appropriate mic input, you are hearing only
the input pre-amp and equaliser sections of the console.
Wind up the mic gain control till you get a PFL meter
indication of about 0 VU on loud notes. Set the monitor level
control to reproduce the tone level of the piano as it is in
the studio.
Can you hear any noise below the programme?
Can you hear any distortion of the notes?
Now back off the monitor level and advance the mic gain control
till the channel peak indicator flashes only on loud notes.
Can you hear more or less noise below the programme?
Can you hear more or less distortion of the notes?
What is the PFL meter now reading (do not worry it will not
burn out)?
It would be OK to run all signals this hot but for one thing.
Back off the monitor level some more and advance the mic gain
control till the channel peak indicator is on all the time.
Sounds bad doesn't it. The gritty distortion you hear added
to the programme is the sound solid state amplifiers make
when overloaded and is called clipping distortion.
The one thing referred to above is your friendly piano player
hitting the next phrase a little louder - pushing the signal
level in the pre-amp above amplifier overload point to produce
the horrible sound we just got - once the pre-amp has clipped
no amount of hard work later on will cancel it. Your mixer
system has a meter calibrated to guide you where to set the mic
gain control so that those extra loud phrases come out clean
too
?
The margin of loudness between the 0VU reading and the