Calibrating Input Level for Plugins

[James Freeman]

Oh, I wanted to know what the dBu and noise floor of the "Secret Sauce IV" Instrument Input, of course the other inputs are noisier and not ideal gain-wise for the models.

 

[MirrorProfiles]

Oh, I wanted to know what the dBu and noise floor of the "Secret Sauce IV" Instrument Input, of course the other inputs are noisier.

Should have these from what I posted above?

I can check the noise with a guitar cable and volume down too, I did have it first with the Lehle connected (but nothing else) which I'd presume is similar to volume down.

 

[James Freeman]

So if I want to record a DI via Input 1 and SPDIF, I have to route the input to Output 1 or 2. If I route Input 1 directly to Output 2 like this:

Then my 0.514V RMS signal comes in my DAW fluctuating between -3.4 and -3.1dBFS. If I go into input 2, directly outputting to Out 2 and then via SPDIF, it comes in at -3.2dBFS without fluctuating at all. -0.36dBu (presumably there is some signal boosting going on between input and output).

Is there no way to directly tap the "Secret Sauce IV" Input 1 to SPDIF?

Look like routing Input 1 to Ouput 1/2 has some level adjustment.
0.514v hitting -3.2dBFS will distort like hell if it actually what's going into the digital amp model.

 

[MirrorProfiles]

I checked again, Secret Sauce Input =17.7dBu (give or take because it fluctuates slightly).

Guitar Volume all the way down:

 

[MirrorProfiles]

Is there no way to directly tap the "Secret Sauce IV" Input 1 to SPDIF?

Look like routing Input 1 to Ouput 1/2 has some level adjustment.
0.514v hitting -3.2dBFS will distort like hell if it actually what's going into the digital amp model.

AFAIK the only options are Input 2 directly to SPDIF, or OUTPUT 1 or 2. I could well be missing something here but its not immediately obvious why I can't route Input 1 to SPDIF.

It would be very useful to record the DI digitally and then the analog outputs for the processed sound. Having to use Input 2 as a DI source for the digital signal just limits things in a number of ways. I also don't understand why the USB and SPDIF values are different for the same source. I have no urge to use the FM-3 as an interface, it would be a massive ballache to reroute my monitoring chain and everything else just to use an interface that only supports one sample rate (and a ton of other limitations).

 

[James Freeman]

There is no way to tap the Input to SPDIF on the Helix either, I can only set the Output 'routing ends' to Digital/SPDIF.
We already confirmed with the Hard Gate that there is no funny stuff going on when nothing is in the routing chain and USB DI is equal to SPDIF output at the end of the chain.

 

[Orvillain]

AFAIK, the only way to route input 1 to SPDIF is to setup a preset that does this:

So output 2 is assigned explicitly to the Digital I/O, and the source is set to SPDIF, not AES or USB.

Then in the preset you've got in 1 routed straight to out 2. You can see out 2 is also set to +4dBu on my unit here. That is switchable to -10dBu.

Then you've got the input levels tab which comes into play too:

I believe the input 1/instrument A/D sensitive knob is used to ensure that the converter doesn't clip, and there is make-up gain applied in the digital realm after conversion to maintain unity gain.

 

[James Freeman]

The grand question is how do I get the cleanest 12dBu signal with the lowest noise floor into my DAW to be used with plugins from the Axe/FM?

If you lower the A/D Sensitivity parameter the noise floor gets higher right?
Any time you boost a digital signal you boost the ADC noise floor.

 

[Orvillain]

If you lower the A/D Sensitivity parameter the noise floor gets higher right?

Doesn't seem to, no.

 

[MirrorProfiles]

shame the FM-3 doesn't have those A/D sensitivity options.

 

[James Freeman]

Doesn't seem to, no.

shame the FM-3 doesn't have those A/D sensitivity options.

That makes me wonder if the ADC stages are the same for Axe3/FM9/FM3 and whether the amp models receive the same amount of gain?

 

[MirrorProfiles]

That makes me wonder if the ADC stages are the same for Axe3/FM9/FM3 and whether the amp models receive the same amount of gain?

You'd hope the processing is accounted for appropriately. Guessing the FM-3 may have lower spec converters and their reference point is fixed, vs what the Axe has where it can be adjusted. The fact that it can't be adjusted suggests its probably optimised already?

 

[James Freeman]

The fact that it can't be adjusted suggests its probably optimised already?

We will never know until someone puts a sine tone through the Axe3 and give us a dBFS reading in DAW via USB.

 

[Orvillain]

Do you just want the sine tone test from the OP doing with the Axe III?

 

[James Freeman]

Do you just want the sine tone test from the OP doing with the Axe III?

Yes please, put a 0.500v RMS sine tone into Instrument Input with the "Secret Sauce IV", and give us -dBFS reading in DAW directly from that input.
Preferably with default A/D Sensitivity setting, if there is such thing.

Also, does changing the A/D Sensitivity changes the dBFS reading?
(it shouldn't?)

 

[Orvillain]

Yes please, put a 0.500v RMS sine tone into Instrument Input with the "Secret Sauce IV", and give us -dBFS reading in DAW directly from that input.
Preferably with default A/D Sensitivity setting, if there is such thing.

Also, does changing the A/D Sensitivity changes the dBFS reading?
(it shouldn't?)

At the default 50% A/D sensitivity, a 0.5v RMS sine (generated by an external synth) measures at -16.5dBFS in the DAW, reading directly from Input 1/Inst (front panel) input.

When I adjust A/D sensitivity down to the 6% figure required for my guitar pickups, it is the same measurement.

 

[James Freeman]

@Orvillain
One last thing, what is the RMS noise floor with the guitar volume at zero?

 

[Orvillain]

@Orvillain
One last thing, what is the RMS noise floor with the guitar volume at zero?

-110dBFS at 50% A/D sensitivity.
-105dBFS at 10% A/D sensitivity.
-102dBFS at 6% A/D sensitivity.

 

[James Freeman]

As expected, noise floor rises as it's compensated digitally.
Thank you again.

 

[Orvillain]

It's not something I can perceive without measuring it. Quieter than a lot of interfaces I've used!