Bedienungsanleitung Allen-Heath ML 3000 (Seite 19 von 48) (Englisch)

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ML3000 User Guide 19

Gain Structure

How the levels between the different signal stages

are set up is referred to as the gain structure. For

best performance it is important that the connected

source signals are matched to the ‘normal operating

level’ of the console. Similarly the levels of the

connected amplifiers and destination equipment

should be correctly matched to the console outputs.

If set too high then the signal peaks will be clipped

resulting in distortion, and if set too low then the

signal-to-noise performance will be degraded

resulting in excessive background hiss and noise.

Using the Meters. The ML3000 provides metering

of inputs and outputs. For best results operate the

console with the LED bar meters averaging around

‘0’ allowing the loudest moments to reach ‘+6’.

Reduce the gain if the red peak LEDs start to flash.

Note that the peak leds light 5dB before actual

clipping to warn that you are nearing distortion and

should reduce gain. The LED bar meters have a

peak response with fast attack and slow release so

that fast musical transients are accurately

displayed. The VU meters have a slower attack so

that the average levels are better displayed. Both

types of metering are useful in live sound mixing.

Matching a Source to the Console. Start by

turning down the channel fader and send levels to

prevent unexpected loud volumes reaching the

main speakers and monitors. Adjust the GAIN

control for an average ‘0’ reading on the channel

meter. Press PFL to listen to the signal using

headphones, local or wedge monitor, and to view its

level on the main LED and VU meters. Once the

gain is correctly set you can raise the levels to bring

the channel into the mix. Note that you may need

to adjust the gain if you make significant changes to

the EQ. Make sure that any equipment inserted

into the channel is set to operate around 0dBu line

level. It is best to first set the gain with inserted

signal processors such as compressors switched to

bypass.

Matching the Console to Destination Equipment.

The console produces a standard XLR output level

of 0dBu for a meter reading of ‘0’. It can produce a

maximum of +23dBu and is therefore well suited to

driving equipment operating at nominal 0dBu or

+4dBu while providing plenty of headroom. If you

are connecting directly to a sensitive power

amplifier it is advisable to turn down its input trim

control if the normal console level is too high.

Simply turning down the console output faders

degrades the output stage noise performance and

reduces the resolution of the fader movement. The

output faders are best operated around ‘-10’ to ‘0’

for loudest average volume required. This allows

plenty of additional headroom if you need it.

Terminology. The normal operating level is the

optimum signal level for best console performance,

indicated by ‘0’ meter readings and resulting in the

0dBu output level. The channels operate at 0dBu

and the mix stages at –2dBu for extended

headroom. Headroom is the extra level available

above normal to allow for loud peaks before the

signal becomes clipped resulting in audible

distortion. The signal-to-noise ratio (SNR) is the

difference measured in dB between normal level

and residual noise floor (hiss) produced by the

console electronics. The dynamic range is the

sum of headroom and SNR representing the

maximum signal range possible from quietest to

loudest.

Using the VCA Groups. Assigning a channel to

one or more VCA groups lets those group faders

control the level of its VCA element. Each fader

provides up to +10dB boost. Note that the channel

VCA allows a maximum combined fader boost of

+10dB. Any more is simply ignored. It is best to

operate the VCA group faders around their nominal

‘0’ position. You can also use a VCA group to

reduce the overall level of a hot mix without having

to adjust all the channel faders.

Final word… A little care with setting gain

structure throughout the signal chain will give you

the very best performance and most manageable

control of the mix.

INPUT

GAIN

INSERT

FADER

VCA

CHANNEL

0dBu

+10

+20

+30

-10

-20

-30

-40

-50

-60

MIX

FADER

INSERT

DIR OUT

EQUALISER

-90

0dBu

+/-15dB+60/-10 dB

0dBu

PAN/BLEND

-3dB law

VCA GROUPS

OUTPUT

MIXCHANNEL

HEADROOM

signal-to-noise

+23dB

-90dB

+23dBu

0dBu

-90dBu

DYNAMIC RANGE

113dB

NOISE FLOOR

CLIPPING LEVEL

SNR-2dBu

MIX HEADROOM

+23dB

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