ALLEN & HEATH ML5000 User's Guide download pdf (Page 19)

ML5000 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 ML5000 provides metering

at all important stages through the signal chain. 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 PAFL (in PFL mode) 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’ and +22dBu

maximum to allow plenty of headroom for driving

equipment hotter. 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. If you are connecting to crossovers

or speaker managers then set these for normal

0dBu operating level and use their level trimmers to

correctly match to the amplifiers.

Terminology. The normal operating level is the

optimum signal level for best console performance,

indicated by ‘0’ meter readings. 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

headroom + 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

VUMIX

OUTPUT

MIXCHANNEL

HEADROOM

signal-to-noise

+22dB

-90dB

+22dBu

0dBu

-90dBu

DYNAMIC RANGE

112dB

NOISE FLOOR

CLIPPING LEVEL

SNR

-2dBu

MIX HEADROOM

+23dB

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ALLEN & HEATH ML5000 User's Guide Page 19

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