DL Meters

[WK154]

It's been a while back on the old Mackie forum that I checked the validity of their centerpiece on the iPad. I was hoping that they quietly fixed the problem but alas no luck. Before understanding the impact of this I suggest reading this for those not familiar with the various metering methods.
http://www.soundonsound.com/sos/jun00/articles/metring.htm
Meters play much more of a role in studio work and mastering than in live application. That said it is still unimaginable that the centerpiece of Mackie's mixer that gets 50% screen real-estate usage  is so inaccurate. The test involved a precision signal generator for input and a quality RMS meter for measuring input and output levels. I used two meters for speed. For the range of the signal generator max at 19 dBu to a low of -52 dBu a 71 dBu range the meters showed a range of 49 dBu. So what happened to 22 dBu? Well at the high end the meters were 10 dBu low and at the low end 12 dBu high. The only place they're even correct is at -6 dB on their scale. At 10 dB in either direction they are already significantly incorrect. So you say so what? Since the mixer doesn't operate in a vacuum and must play with other gear that typically understands dBu it matters. I have seen some really bad gain structures in my day so nothing surprises me anymore. Here's my take on this. Either fix them to be correct or relegate them to a 1" high graphic that shows all of them and use the freed up screen space for more useful information or control. Mackie is well aware of this but obviously considers it irrelevant, so much for quality. The mixer also looses 2.94 avg. dBu from input to output. This is with unity gain and input and output faders at 0. The clip indicator triggers at -5 dBFS not at -3 dBFS as stated in their manual. I call this just sloppy work.

[RoadRanger]

Last time I looked in the manual (page 39 in the latest) it was quite clear that the meters have no scale - the scale you see near them is for the fader.
"Red [clipping] = –3 dBFS
Green to yellow = –18 dBFS
Green [bottom] = –90 dBFS"

[WK154]

If you read the text it can't be any plainer " The input meters (next to each channel fader) displays the signal input level to the channel......" I just checked the transition from green to yellow and find it at -13.7 dBFS so much for their info.

[RoadRanger]

How did you measure FS ?

Oh, and I agree it's rather silly to have the faders calibrated with a "nominal 0 dB", the meters in dBFS, and have them aligned physically like that but not with the same scale or at least an offset scale with the same "dB per mm" at a given position .

[WK154]

How did you measure FS ?

I made the assumption that something is correct in their specs and that 0 dBFS = 21 dBu measured at 7.38 dBu (1.84V RMS) makes the -13.68 dBFS. I also checked this a while back and actually got 23 dBu out of the DL (no speaker on) .
Update: Actually there is a dead zone which covers = -13.68 to -14.45 dBFS for an avg. of -14.01. -18 dBFS my foot.

[RoadRanger]

How did you measure FS ?

I made the assumption that something is correct in their specs and that 0 dBFS = 21 dBu measured at 7.38 dBu (1.84V RMS) makes the -13.68 dBFS. I also checked this a while back and actually got 23 dBu out of the DL (no speaker on) .

Probably a bad assumption - on digital crap FS on the inputs is usually when the A/D converter clips so you should measure against that. Actually I was fooling around a bit last week trying to see if the preamps clip before the A/D converters and I wasn't sure - the clipping sounded a bit "rounded" to me but I didn't have a scope hooked up. Maybe as long as you're in the mood you could take a look for us?

[WK154]

How did you measure FS ?

I made the assumption that something is correct in their specs and that 0 dBFS = 21 dBu measured at 7.38 dBu (1.84V RMS) makes the -13.68 dBFS. I also checked this a while back and actually got 23 dBu out of the DL (no speaker on) .

Probably a bad assumption - on digital crap FS on the inputs is usually when the A/D converter clips so you should measure against that. Actually I was fooling around a bit last week trying to see if the preamps clip before the A/D converters and I wasn't sure - the clipping sounded a bit "rounded" to me but I didn't have a scope hooked up. Maybe as long as you're in the mood you could take a look for us?

Actually it's the only assumption you can make since we are looking at a black box and the only thing measurable is input and output signals. Unless of course you want to take it apart and measure A/D levels. Where did you get this preamps clipping thing? They will become nonlinear near their rail voltage and max out. A/D will clip once input level is exceeded. In any case none of this is available to measure. The 21 dBu max is 24.5V PP and the rails are at either 30 or 32V. Plenty of margin for the preamps.
Actually record could come in handy since it is looking at the A/D only.    Hmm got to see what that means but right now it's still under test for sync problems. It'll have to wait.
Keep in mind that my generator only goes to 19 dBu and the only other thing I have that would do the job is in mothballs a HP3330 85lbs monster I'm not willing to drag out for the DL.
P.S. I'm also a little preoccupied by an X32 and that honey-do list.

update: Behringer to the rescue I have a UB1202 that goes to 22dBu just enough, now to find the cables.

[Wynnd]

Personally, I've always considered meters to be reference points and not absolutes.  (Exception is my DB meters.  Those need to be moderately accurate.)  As long as they are off about the same across all inputs, they will be functional for my needs.  I'm still not hearing any clipping or distortion at the levels I'm running.  That strikes me as the preamps are pretty forgiving. 

[WK154]

Wynnd as I stated before accurate meters are far more important to mastering or studio work, were one would spend $1200 for a Durrough meter (more than a DL), than live sound. But would you be happy if your gas gauge shows that you have gas and you run out of it? As to the preamps their claim is 109 dB of dynamic range for the mixer that's from +21dBu down to -88 dBu (A weight) more than sufficient for live sound. I would expect the A/D and D/A converters to be the limit not preamps. The 109 dB comes from the weakest link in the chain the A/D converter.

[Wynnd]

Love the gas gauge comparison.  I own my second Pacific Coast and the fuel gauge reads empty with about a gallon left to burn.  It's only a 4.2 gallon gas tank so that last gallon is very useful when riding cross country.  (There is no reserve valve.  When the tank is empty, it really is empty.)  Both motorcycles fuel gauges read just about the same.  When the fuel gauge needle is pointing to the fuel pump's hose, you had better find gas quickly. I'm sure there are many people who need much higher accuracy then I do.  They probably aren't looking at this mixer and are much more likely to look at mixers costing $5K or much more.   Thanks for the info anyway.  Might be important to me at some point.  (When was the last time a live band utilized more than 30 db of dynamics?)

[WK154]

Wynnd you'd be surprised at how many hit CD's were produced on CR1604 Mackies and if you're on a budget it would have to do. My point in all this is that Mackie could just as well have made it consistent instead of what they did which is mix analog data (input and output, absolute) with digital data representation (relative). Once you finalize a design all relationships between analog and digital are fixed (A/D and D/A) and could have easily been kept in the analog world instead of this mishmash. To make matters worse they don't follow the dB definition (it's non linear). As to the live band it's like your Honda with a speedometer that goes to 130mph but you never exceed the speed limit! 
P.S. I thought you'd like that.

[Wynnd]

The Pacific Coast's speedometer does indeed go to 130 mph.  The bike is supposed to be able to go 115 mph and I've never been above 95 mph.  (Things happen way too fast over three digits and it takes forever to stop.)

[RoadRanger]

Damn, I've got to get my PC800 back on the road one of these days ...

[Wynnd]

Mine is headed to Washington State this summer for a ride with my Brother.  (He has a Triumph America.)