Pro Tools signal generator sine wave creates harmonics / overtones?

[atticmike]

Hello there,

Is it normal that Pro Tools' sine wave generator creates harmonics / overtones?

Or is it the Pro Tools engine creating the overtones?

[joachim]

Is it happening with less than 0,0 dBfs, too ?

[atticmike]

Originally Posted by joachim

Is it happening with less than 0,0 dBfs, too ?

Well it happens at -3.1 rms sine upwards, not in peak mode obviously, not enough level.

But when I put it to 3.1 where the overtones don't happen and add a trim plugin, compensating for the missing 3.1, no overtones whatsoever.

Is that a built in feature? Or a bug?

[joachim]

From wikipedia :
"RMS: For the case in which the RMS value of a full-scale square wave is designated 0 dBFS, all possible dBFS measurements are negative numbers. A sine wave cannot exist at a larger RMS value than −3 dBFS without clipping by this convention."

The clipping produces those overtones, so I would not call it a bug but physics/mathemetics.

[Rich Breen]

Sine wave generator in PT does not generate significant harmonics. I see nothing but red lights in your screen shot, so yes, everything's clipping.

[atticmike]

Originally Posted by joachim

From wikipedia :
"RMS: For the case in which the RMS value of a full-scale square wave is designated 0 dBFS, all possible dBFS measurements are negative numbers. A sine wave cannot exist at a larger RMS value than −3 dBFS without clipping by this convention."

The clipping produces those overtones, so I would not call it a bug but physics/mathemetics.

Well how do you explain that I was able to raise the level with a trim plugin while harmonics didn't occur? Pro Tools 12's engine runs at floating point so there shouldn't be any level restriction, which explains why if I stop at -3.1 and add more gain with the trim plugin, it will not create any harmonics whatsoever and I can stack this signal as much as I like.

Don't throw in physics and mathematics if you can't recite fourier formulas...

Originally Posted by Rich Breen

Sine wave generator in PT does not generate significant harmonics. I see nothing but red lights in your screen shot, so yes, everything's clipping.

And as for you, Mr. Burbank, if you looked a little closer, you'd see that I've merely monitored the signal, which does not pertain to any harmonics displayed. But what did I expect, to ask Pro Tools users for theoretical, system oriented and non-production based questions... How do you explain then that on the right side, I can go past that level by not going beyond -3.0 and using a trim plugin to compensate? Surely trim should clip now, BECAUSE IT IS ALL RED oO Sometimes, I feel like people still mix like it's 2004.

Anyways, solved it, it is the signal generator which generates some kind of harmonics past -3.0 rms.

[musicman691]

Originally Posted by atticmike

Well it happens at -3.1 rms sine upwards, not in peak mode obviously, not enough level.

But when I put it to 3.1 where the overtones don't happen and add a trim plugin, compensating for the missing 3.1, no overtones whatsoever.

Is that a built in feature? Or a bug?

How about showing us your 'evidence' in a signal analysis plugin and NOT some EQ or channel strip plugin? Then we'll talk. I've done enough signal analysis that I should be able to separate the bs from the chaff.

[atticmike]

Originally Posted by musicman691

How about showing us your 'evidence' in a signal analysis plugin and NOT some EQ or channel strip plugin? Then we'll talk. I've done enough signal analysis that I should be able to separate the bs from the chaff.

Right above, you can see the bluecat analysis tool. which has nothing to do with channel strips if the metric halo plot irritates you.

[musicman691]

Originally Posted by atticmike

Right above, you can see the bluecat analysis tool. which has nothing to do with channel strips if the metric halo plot irritates you.

Where in the chain is the BC plugin - before or after the MH plugin? To make your point that the signal generator is creating harmonics you really need to have the BC plugin before the MH strip and not after. Because if it's after you're not really able to prove your point about the generator plugin right?

[Rich Breen]

The screenshots are a bit too fuzzy for me to tell what's going on, and I'm not gonna dig into this deeply, but it is worth saying that the PT sig generator has never been the cleanest thing out there - sufficient for checking gain structure, setting interface levels, etc, but I certainly wouldn't rely on it for any kind of real "analysis". If I need pure tones for distortion tests, linearity sweeps, aliasing tests, etc, I generally use the programmable generator in Spectrafoo which works quite well and can do just about anything I need. That said, those screenshots sure look like something else is going on - distortion products 10dB down - seems like clipping somewhere in the chain to me...