Mackie M1200/M1400 owner manual Next set the master output level fader, Dynamic Range

the component and the nominal signal level. It is important to maintain a reasonable amount of headroom so that the dynamic transient peaks of the musical program can be reproduced without clipping. 10 dB of head- room is usually adequate, but some program material may require up to 20 dB.

Next comes the output level of the channel, controlled by a fader or rotary gain control. Faders usually have an indication in the graph- ics that shows the normal or nominal setting for the fader. This setting is usually 10 or 12 dB below the maximum output level of the chan- nel. This provides the headroom needed to reproduce the transient peaks associated with music. If the channel has a meter, you can use

40dB

30dB

20dB

10dB

0dB

–10dB

HEADROOM

DYNAMIC

MAXIMUM OUTPUT LEVEL (M•1200 = 400W/4Ω )

NOMINAL LEVEL (25W/4Ω )

that to visually confirm that the nominal output level of the channel is around “0” on the meter.

Next set the master output level (fader)

control on the mixer to the nominal level indi- cation next to the control. Again, this should be

–20dB

–30dB

–40dB

–50dB

–60dB

–70dB

–80dB

SIGNAL TO NOISE

RATIO

RANGE

NOISE FLOOR

at least 10 dB below the maximum output level of the mixer. You can double check the actual output signal level if there is an output meter on the mixer. On most professional equipment, this nominal output level will be +4 dBm (1.23V rms into 600 ohms).

The output of the mixer may drive a power amplifier directly, or it may go through a signal processor first (i.e., equalizer, compressor lim-

Dynamic Range

The best way to accomplish this goal is to optimize the input and output levels for each component in the system. It is best to start at the beginning of the chain (the microphone) and work your way to the end (the speakers). The following procedure details how to opti- mize a sound system with 10 dB of headroom.

A microphone is connected to the mic input on the mixing console. The gain of the mic preamp circuit, sometimes called Mic Trim, should be adjusted so that the loudest micro- phone signal is just below the overload point of the preamp. Most mixing consoles provide a mic preamp clipping indicator or level meter- ing of some kind to optimize the mic preamp.

iter, crossover). Determine the maximum output capability of the signal processor. Hopefully, it can produce at least +14 dB to maintain the required 10 dB of headroom. Chances are it can produce considerably more than that (like +20 dB to +24 dB). If 10 dB of headroom is not available, you’ll have to intro- duce a resistive pad between the mixer and the signal processor to reduce the signal level from the mixer so it is at least 10 dB below the maxi- mum output of the processor.

If the processor has enough headroom, set the level controls to unity gain, so with a +4 dB input it produces a +4 dB output. Keep in mind that if this is an equalizer, and you’ve boosted several frequency bands, the nominal output level may be more than +4 dB because of the extra energy the processor is adding to those frequencies. It may be necessary, in that case, to reduce the level controls a few dB below unity.

The M•1200/M•1400 amps are designed to accept a nominal +4 dB input signal. Set the GAIN controls fully clockwise. This will pro- vide the best signal-to-noise ratio and available headroom for the amplifier.

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