Is Pro Tools metering questionable?

[Doctor Swing]

Now here's something very scary.
It is a friend of mine who found out about the following, but I checked for myself and it is true...

Create a new session in 24 bits resolution, let's say 8 tracks if you have a 192 interface. My session was in WAV format, running at 48kHz.
Arm all eight tracks from inputs one to eight.
You need an external tone generator with plenty of gain (we both used our console's 1kHz generator with an outboard SSL XLogic channel to get enough clean gain in order to reach 0dB full scale. I also need you to monitor the ouput of your system.

Feed the 1kHz tone to one input at a time, crank up the gain, until you hear it distort. Check the session meters. Do this for every single input.
Strangely, you will find out that several inputs out of 8 will distort before turning red on the session tracks meters. The other ones will distort once you're in the red. If you switch the track i/o volume window to peak, you'll see that it distorts once you hit 0dBFs. (That's reassuring) but on the misbehaving tracks, it takes a whole lot of gain before you hit the red "led". On the other hand, if you look at your 192 interface meters, they all turn red when they should (once you hit full scale).

This is very annoying. Let's say you're tracking drums, with a whole bunch of tracks. Sometimes, you need to trust the meters, because distortion can be hidden in the tracking mix, or happen on one hit on the whole take, right? Well, you might be hitting full scale and beyond without the tracks turning red!!!! How can you trust your system then?
I'm wondering if someone else has witnessed the same thing out there. I did not checked other interfaces myself, yet. My friend says the 96s inputs are responding ok. I wonder about the 888s, Digi001 and 002,...
Is this a bug? It seems that there is a problem of communication between the software and the analog inputs of the 192 interfaces...
Amptec, one of the most serious Digidesign dealers in Belgium has been kind enough to swap interfaces, just to make sure we did not have faulty hardware. They also personally recalibrated the interfaces. It does not make any difference. One more detail : each 192 interface has a different set of track measuring wrong... hihihi...

Oh, and I forgot, I tried this at 16 bits and the system works fine...

Time to do a little research for yourself and share...

[crizdee]

Hi,

So both you and your friend have tested this independantly! and you have tried 2 192's. well i was going to suggest the input trimmer pots? but i guess you have checked this!? have you been able to try using just the digital inputs for testing?

Chris

[mampam]

I just tried it and found that the only "distortion" was on the front end of my console if I did not compensate for the increased output of the 192. Perhaps that is your problem?

[minister]

Amptec, one of the most serious Digidesign dealers in Belgium has been kind enough to swap interfaces, just to make sure we did not have faulty hardware. They also personally recalibrated the interfaces. It does not make any difference. One more detail : each 192 interface has a different set of track measuring wrong... hihihi...

sounds to me like YOU need to calibrate the 192 yourself. i would not trust a dealer to calibrate it. buy a Multi-Meter that has a high enough resolution that it can read 1.228v.

audio post in the states use -20dBFS = 0 VU (or +4 dBU, or 1.228V)
audio post in europe (and other places) use -18dBFS = 0 VU (or +4 dBU, or 1.228V)
the american recording engineers i know use -18dBFS = 0 VU (or +4 dBU, or 1.228V)

some radio production people use -14dBFS = yadda, yadda.

aligned with a 1K tone.

with the multi-meter, test the lines feeding the 192 to make sure they are dead on. then feed your 192 and calibrate the levels going into the 192 by adjusting the trim post on the front. then, feed a 1k tone out of the 192's and make sure that the each outgoing channel is dead on to 1.228.

THEN your 192's are calibrated. you might be surpised! my 192 was WAY out of whack when i got it. it was the first thing i did. and now i know.

[Doctor Swing]

Hi everybody!

Thanks for your reactions...

I think the problem is somewhere else. I can ensure you that this is completely independent of the 192 calibration (the fact is that it behave exactly the same way on every trim pot positions (audible saturation at fs BEFORE red led in the software) The ONLY variable is the the 192 input number!

The mystery is between the interface and the software...that's my opinion

[Doctor Swing]

and...don't forget that the system works fine in 16 bits!!!! héhéhé

X

[Jeff D.]

Make sure you don't have Soft Clip on in the hardware setup window. Soft Clip will cause clipping before 0db, just as you described.

Jeff D.

[Doctor Swing]

Checked: No soft clipping engaged!

Thanks

X

[c-tone]

Getting anywhere close to the red is VERY hot when sending a sine wave. You might even be disorting the output of your oscillator - it's not really made to send out levels that hot. Don't forget that the 192 is probably calibrated for 0 VU = -18 db, which I think means 0 db is probably +18 VU. It probably is the 192 ouput that is distorting, and possibly the front end of the console line ins. This is why I run my rig at -16, so that I get less level on the outputs. This is also why when I record tracks with very little transients, like bass, vocals, and distorted guitars, I keep the level pretty darn low to the Pro Tools inputs (like not even in the yellow on the 192 meters). Anyone who mixes out of Pro Tools on an SSL with VU meters will tell you how the meters slam on those kind of tracks when they are recorded hot, and you can get distortion.

Also, you are right that the 192 and Pro Tools metering is lousy, in that there are no real numbers anywhere on a meter that say what the levels are, like almost any console would have. The four segment led's on the 192 are almost useless, and the 888's were far superior in that regard. Hopefully, they will make the software meters better soon.

[c-tone]

sorry I just re-read your post. I see you needed to use an extra channel to get enough gain to even get the signal generator level that hot. That right there should tell you that this is not a normal level that is used to set up and test gear.