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DJM 900 LED meters + Nexus USB Output level?

Hello there.

I was wondering about the LED meters on the DJM 900.

1) The numbers on the LED channel and master meters are dBU right?

If so, is there a reason why 0dBfs = +4 dBu instead of -18 dBu line level on the mixer? I did a test using a test oscillator and the signal came through as +4 on the LED's

2) How loud should the signal coming into the inputs be for the mixer to work at its optimum potential (i.e like line level on analog gear)

3) what is the DAC converter in the DJM 900 calibrated too?

Also, what exactly does the 'USB output level' feature on the DJM-900nexus Setup Utility do? I'm changing it through -5, -10, -15, -19 and nothings being attenuated on the mixer LED's. Am i missing something?

 

Thanks in advance for anyone who lends some advice on these issues!

Freddie

AlmostInstant

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You can aim for the +4dB mark for optimal SNR levels across channel and master.  It's not -18 because that's the overhead on the mixer.

The incoming signals should be line level (1.23V) for analog or whatever the digital level signal voltage is.

I don't know what the DACs are calibrated to and we're unlikely to get that data from the engineers.

The output setting level is for the digital output / USB output levels.

Pulse 0 votes
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Thanks for the fast reply Pulse.

Just to verify, the numbers on the LED channel and master meters are dBu right?

Okay great, i'll aim for +4db. What do you mean when you mention -18 as 'overhead on the mixer'?

I should have included that i was testing the 'USB output level' with my computer playing audio through the DJM interface and not through the line RCA inputs. I was switching the USB output level and nothing was happening to the audio going into the mixer from my computer. What exactly does the function do?

Thanks again for your time.

AlmostInstant 0 votes
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They're supposed to be reflecting dBu, yes.

The mixer has 19dB of headroom, allowing for that much volume jump before you really hit the clip level, which as you know in a digital world, is the worst thing you can do!

As noted above, the setting for the output level changes the master output level sent over the USB; you should see that change reflected in the output levels recorded in your software.

Pulse 0 votes
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Ok, thanks for the info

So just to verify, from the OVER on the channel LED meter there's an extra +19dBu until the signal digitally clips? Or the audio signal digitally clips on the DJM 900's channel meter at +29dBu.

What i'm trying to understand is why when i put a 0dBFS signal (from a testosc) through the djm900 Interface it shows up as +7dBu on the LED channel meter. A 0dbFS should be way above line level and -14 dBFS should be around +4dBu or +7dBu.

I see, sorry about the misunderstanding i was trying to see what the change was on the mixer.

AlmostInstant 0 votes
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The mixer has 19dB above the zero mark, not above the clip lights.

If you're putting a 0dB signal into one of the channels, adjusting the gain and master levels until you have the same output signal level is what you want to achieve.

Pulse 0 votes
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Hey DJ Kiki yeah you're right 0dbFS is digital zero and it should be around +19db on a typical dBu meter built into analog gear (normally it's a dBVU meter, which is just RMS and 0dVU = 4dBu) but on the DJM 900's meters the 0dBFS registers at +7dB, there's some attenuation going on but i'm not sure why it's there or where it's there. I have looked in the manual at the block diagrams of the DJM 900.

"0dB at mixer is -19dBFS, right? <--- I think you've got confused with where the line level should be at and 0dB. Line level at +4dBu registers around -15dBFS to -22dBFS on a digital system depending on calibration.

In terms of this mixer a 0dBFS signal is actually showing at +7dBu on the meters.

 

AlmostInstant 0 votes
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@KIKI > Yes, I know that -- just missed it during discussion above, but that doesn't affect the outcome of the conversation.

With line level registering at +4dB and for digital that's -15dBFS; that gives you the 19dB of headroom as indicated.  0dBFS shouldn't be at +7dBu; have you adjusted the master attenuator?  It has settings for -6dB, -3dB and 0dB. 

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The master attenuator is under the DJM 900 UTILITY menu right? The one accessed by holding down the Midi ON/OFF button.

If so, i looked under that menu and the option wasn't there.

I looked in the manual and saw that there is a 'user' and a 'club' version of the menu, is this correct? 

AlmostInstant 0 votes
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I've checked under my DJM UTILITY settings and i'm unable to access the master attenuator. It doesn't show up and give me an option to change it. The menu stops at TALK LVL. Is there something i'm missing?

AlmostInstant 0 votes
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@AlmostInstant > Yeah, you forgot to read the manual closely. :)

Here is what you must have missed:

"To display the [CLUB SETUP] mode setting screen, first turn this unit’s power off, then press the [POWER] button while pressing the [ON/OFF (UTILITY)] button."

 

 That should provide you with access. ;)

Foster 0 votes
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So it is, guess that's a lesson to read the manual more closely.

Thanks Foster.

AlmostInstant 0 votes
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The master attenuation of my mixer is set to 0db in the settings.

I think i have an idea as to why a 0dBFS signal is registering at +7dBu on the channel LED meters through the CD/Line input.

I'm not too experienced with digital -> analog gain leveling & metering so please excuse me.

In the manual on Page 26 it shows the CD/Line input level being at -12dBU.

You mention that the clip/headroom of the mixer is at +19dbU so a track coming through as 0dBFS should be up at +19dB or as hot as that. (Without Input attenuation)

So minus the 12dB from the headroom and you get +7 with the trim set at unity. Am i correct to think this?

AlmostInstant 0 votes
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A 0dBFS signal?  I'd recommend not worrying about what 0 on the meters corresponds to.  Just put the master where its meter is the same as the channel meter.  Zero on a meter like this is just meant to give a a somewhat arbitrary reasonable spot to have your average peak and troughs symmetrically bouncing around it while being comfortably far away from the hidden max clip point that you will neither reach nor clip with any musical content if you abide by that recommended area.  It's not the exact point a 0dBV reference signal should hit with every input source that is put in.  But yes, the Pioneers don't actually even go up to 0dBFS, rather like -4.4dB.  Not a big deal.  The input AD converters also won't clip until after "over" or "clip" is hit on the DJM900s, but you shouldn't be close to that high, even if you get some smidgen of extra S/N ratio pushing it near there.  Be wary that reduced EQs will give a false sense of the level going in, as the meters are post converters.  There's otherwise no optimal level converters are designed for.  Master out attenuation and USB out level don't affect the mixer's meters, either, just how hot it is coming out of the unit.  This setting is also bypassed if it's set for timecode.

Reticuli 0 votes
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@Reticuli > I appreciate that you've gone into your time machine to dig up this 5 year old thread to contribute an answer.

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