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Mixer direct out reference level
Old 4th March 2014
  #1
Lives for gear
 
🎧 10 years
Mixer direct out reference level

My Allen & Heath board has +4dbu L/R outputs but the direct outputs for each channel is at +0dbu.

Why is this and does this mean that there's actually 4 decibels of extra gain on the direct outs compared to the L/R outputs?
Old 5th March 2014
  #2
Lives for gear
 
🎧 10 years
There's a 4 decibel difference between the two. Is that the only difference? If so I'm wondering why they decided on making the direct outs 0dbu.
Old 6th March 2014
  #3
Lives for gear
 
🎧 10 years
Anyone?
Old 6th March 2014
  #4
Lives for gear
 
🎧 15 years
Just a general reply as I've got no experience with A&H boards. You can list your specific A&H model along with your test methods and may find more help in the Geekslutz subforum here. Not knowing what/how you tested but +4 can be measured as a specific voltage with a multimeter at both input / output points. Additionally many mixer modules will have trimable resistors for calibration.
Old 6th March 2014
  #5
Lives for gear
 
1 Review written
🎧 15 years
Pretty much every analog console reduces the level within the channel strip. This is how you get 'gobs of headroom.' They know you'll be putting too much level into it, so everything is attenuated inside!
Old 6th March 2014
  #6
Lives for gear
 
🎧 5 years
Quote:
Originally Posted by HSLand ➑️
My Allen & Heath board has +4dbu L/R outputs but the direct outputs for each channel is at +0dbu.

Why is this and does this mean that there's actually 4 decibels of extra gain on the direct outs compared to the L/R outputs?
Most professional audio equipment is calibrated to produce a nominal signal level of +4dBu from the outputs. That means, when you're running the board at an output level that hovers around "0" on the main meter, the voltage produced at the outputs is about .774VAC RMS. As I said, this is a common standard for pro audio; consumer-grade equipment tends to use a standard of -10dBV (different reference voltage; +4dBu ~= 1.8dBV, so -10dBV is about 12dB weaker than +4dBu), because consumer-grade equipment is expected to have lower attenuation from travelling through long cable runs (XLR snakes can exceed 300 feet, about 30 times the longest realistic expectation for a home theater cable run).

Now, not all inputs or outputs of the system run at +4dBu; the line-in of the GL2400 (for which the numbers you've given line up) operates at 0dBu nominal voltage. The direct outs output a post-EQ version of the signal, and as such they also operate at 0dB. When sending the direct out of a channel to another channel (on the same mixer, another mixer, or an ADC), the channel receiving the direct out can simply be set to unity line-level gain to give the second channel the same level as the channel sending the direct out.

The insert of the channel outputs at -2dBu. The most logical reason for this is that the most common use is to plug the channel into an outboard effects unit, and that unit, if it works by adding a new waveform to the existing one (as it the case for most "synth"-type effects like chorus, reverb, delay, phasing/flanging, etc) and it's running at unity gain relative to the input, will increase the nominal signal level of the output by 2-3dB. The reduction in send signal level compensates for this.

The mixer, in turn, will combine varying levels of several channels, and combining two in-phase signals of equal strength will produce a nominal 3dB increase in signal level. That means the downstream buses - the groups, auxes and masters - need more headroom than the channels themselves, hence the +4dBu output bus nominal level.
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