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Old 08-23-2007, 09:54 AM
thermionic thermionic is offline
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Join Date: Dec 1969
Posts: 637
Originally Posted by konbit
Does it really make any difference, sonically, if you are running your master at 5 and your channels at 9 versus your master at 9 and your channels at 5?

Yes. It makes all the difference.

Not trying to upset anyone, but it’s pretty scary that so many DJs do not have a grasp on what is the most elementary concept any DJ should know...

If you bring up the Master Amp, you bring up 6 channels' worth of noise…

If you bring up the Channel Attenuator, you bring up whatever noise is present solely on that channel…

Can anyone see what I’m getting at here?

As anyone who’s watched Spinal Tap will know, the numbers on any Level Attenuator / Gain Trim, Input or Output, are relative. That is to say that (if we talk about line-level operation as an example) ‘9’ has a totally different meaning if your input is from a -10dbV source as it would do if your input is a +4dBu source.

View the Input Attenuator pot as a ‘tap’ on a pipe that adjusts volume of water flow. If you have a hot source, say a professional D-A converter, you risk overloading the mixer’s input buffer if you run the control high. Likewise, with a pro-sumer D-A converter with a weedy output, you may need to run it really high as you don’t want to compensate with the Master for the above reasons.

If the post-Input pot Buffer is going to clip at say, +16dBu, it will clip at that level regardless of whether the Pot is at '3' or '10' - it's all down to how hot the incoming signal is.

As you can see, the number on any Input Attenuator is an arbitrary figure that is RELATIVE to what signal is going in – the numbers on their own have no meaning whatsoever.

In the case of the Master Output, regardless of what’s connected, you have a control with 6-channels’ worth of noise… Therefore, it’s worth getting as much undistorted level as you can, PRIOR to the mix-buss.

Another thing: ‘Red’ means nothing, as does ‘Green’ – you could have an LED with polka dots if you want. Again, everything is RELATIVE – according to how the unit is calibrated. Take the Rane MP24 for example; it has a meter calibration control. On an MP24, you could set the Red light to come on at 300mV RMS output – or – 1v RMS – it all depends on calibration.

One mixer could have high-voltage rails and put out +22dBm without clipping, whereas another mixer might have 2% distortion at that level… Where would ‘red’ be in this case?

Please understand that in the case of Gain Structure (any studio engineer will tell you their entire professional life is dedicated to respecting its principles), everything has to be evaluated on a case-by-case basis; there has never been and never will be one rule for all – it always horses-for-courses. Gain Structure is a totally academic concept which can be approached empirically (most DJs aren’t engineers) and optimised as such. However, it CANNOT be approached with crass generalisations about dial markings or LED colours – it’s all RELATIVE.

Note that the only exception is digital, where regardless of whether you have 16 or 24 bit, you cannot exceed 0dBfS. In the analogue world, you could have one mixer that distorts at +12dBu and another mixer that runs clean past +20dBu – it’s all down to design and headroom – something that’s specific to each mixer.

Links that follow this up:

(Last link is quite pertinent)


Last edited by thermionic : 12-04-2007 at 03:44 PM.
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