Calibrating Input Level for Plugins

[MirrorProfiles]

Still getting the 5dBu value. If I set "Clean Sens" on the Kemper to around -7dB, then the SPDIF output gives +12dBu of headroom in the DAW.
With everything at 0, the converters easily clip from humbuckers and sound awful. I read something on Kemper's forum about it having a soft clipping circuit but I couldn't really find much information about it. The waveforms do look slightly less dynamic than the Avalon DI above, I'm not sure if thats because its a slightly lower impedance, or some kind of soft clipping, or something else. They sound similar in volume, the 5dBu one is noticeably louder (hard not to be distracted by the clipping).

The manual does note that this is an important parameter (as I quoted above), and it also mentions that you wouldn't notice the clipping on high gain sounds (true but how about just not clipping at all?). GUESSING that clean sens is somewhat like the pad's on fractal units, where it'll compensate the amount of padding back up internally.

Anyway, if anyone here is using a Kemper as a DI box for using other stuff, I'd recommend setting clean sens to AT LEAST -7dB (if you'd like 12dBu of headroom). and if its your reamp box via SPDIF, then be aware that at reamp sens=0, its set up for a 5dBu signal. Boost it to +7dB if you want your NAM models or reamps to be gain staged correctly for a 12dBu input

 

[James Freeman]

Kudos to Kemper who got it all figured out eons ago.
Same dBu at the input and reamp output, compensated Pad and output.

The man knew what the hell he was doing right from the start.
German ingenuity.

 

[DLC86]

Kudos to Kemper who got it all figured out eons ago.
Same dBu at the input and reamp output, compensated Pad and output.

The man knew what the hell he was doing right from the start.
German ingenuity.

I think Cliff figured that out even before, iirc even the axe fx standard had automatic input gain compensation and unity gain outputs. For sure the axe fx II, which came out a few months before the kemper, had these.

Anyway, kudos to both

 

[Deadpan]

Measured again, checking everything as I go and verifying against other devices.

With Kemper settings at 0 (clean sens, reamp sens), I’m measuring the headroom to be at 5dBu.

To get it set up for 12dBu, I had to set clean sens to -6.9dB and reamp sens to 7.1dB (sending a -15.9dB sine wave in via SPDIF)

5dBu seems really low to me - the fact I’m measuring it on input and output makes sense though - it means it works as intended and will preserve gain levels. Might be good if someone can verify this though.

For a short time Kemper lowered the spdif volume by 8db, we all had a fit and he put it back.

I do all my captures based on the Kemper Spdif volume.

 

[MirrorProfiles]

For a short time Kemper lowered the spdif volume by 8db, we all had a fit and he put it back.

I do all my captures based on the Kemper Spdif volume.

do you keep everything at 0? and do you use the kemper DI generally? or do you use different DI’s for different gear?

I can sort of see why Kemper would have increased the headroom, 5dBu is almost guaranteed to clip if you’re recording DI’s via SPDIF

 

[Deadpan]

do you keep everything at 0? and do you use the kemper DI generally? or do you use different DI’s for different gear?

I can sort of see why Kemper would have increased the headroom, 5dBu is almost guaranteed to clip if you’re recording DI’s via SPDIF

I keep all at 0. Clips only if I use my hottest guitar and strum harder than I ever would.

 

[Josetxu]

Kudos to Kemper who got it all figured out eons ago.
Same dBu at the input and reamp output, compensated Pad and output.

The man knew what the hell he was doing right from the start.
German ingenuity.

Although I'm a fractal user now, I always thought Kemper was very well though when I owned it.

 

[MirrorProfiles]

Absolutely LOLing at myself for how much I need to get a life, but I had a very pleasant chat with Softube today on their 15 minute zoom call service thing. The guy I spoke to asked their devs and got me a nice answer of 3V = 0dBFS, which he said is roughly 12dBu (which I believe is correct if its V RMS).

Took a while to get that information, but I have to say that some companies deal with their customers better than others, and when you use their products for years and have certain bugs or things come up you get an idea of what they're like. Softube really do have excellent customer services and are friendly, helpful and respectful and really go above and beyond more than I've seen from a lot of companies. Just thought its worth mentioning because we're so spoiled for choice, and in a crowded marketplace I think its worth highlighting the companies who are trying to do things the right way.

 

[Deadpan]

I hadn't thought much of this issue before as with TH-U the Kempers spdif hits perfectly with no adjustment.

Note: When Kemper's input "clips" I hear no audible nastyness.

I just tested a few different interfaces and this is more of an issue than I thought...

 

[James Freeman]

I just tested a few different interfaces and this is more of an issue than I thought...

Yep.
The interfaces are all over the place, the plugins are all over the place.
Plugin manufacturers claiming superior accuracy while completely disregarding the customer end where randomness and chaos rule supreme.

 

[Deadpan]

Yep.
The interfaces are all over the place, the plugins are all over the place.
Plugin manufacturers claiming superior accuracy while completely disregarding the customer end where randomness and chaos rule supreme.

Question for you, when you calibrate for 12dbu does the amp have the same gain in the room from your interface as plugged straight into the amp?

 

[MirrorProfiles]

Question for you, when you calibrate for 12dbu does the amp have the same gain in the room from your interface as plugged straight into the amp?

I’m not James but I can answer…. Having that same amount of gain as plugging directly into the amp is exactly the point of calibrating the DI and reamp box correctly. It can be to any value (not just 12dBu) depending on how much headroom you like on your converters. If you know what the destination (i.e reamp box+real amp, or plugin emulation) are set up for, then you can adjust your input level accordingly.

 

[James Freeman]

Question for you, when you calibrate for 12dbu does the amp have the same gain in the room from your interface as plugged straight into the amp?

My interface is +8 dBu, it's an older Focusrite Saffire (firewire).
For +12dBu captures and plugins I have to attenuate my input by 4dB.

If the audio interface has +12dBu instrument inputs (at minimum gain), you want to send a capturing test signal from an Output that is calibrated to +12dBu, that way the capture itself is automatically ready for +12dBu inputs.
THEN yes, it will be exactly like plugging into the amp.

 

[Deadpan]

My interface is +8 dBu, it's an older Focusrite Saffire (firewire).
For +12dBu captures and plugins I have to attenuate my input by 4dB.

If the audio interface has +12dBu instrument inputs (at minimum gain), you want to send a capturing test signal from an Output that is calibrated to +12dBu, that way the capture itself is automatically ready for +12dBu inputs.
THEN yes, it will be exactly like plugging into the amp.

Perfect. That works as expected. Thanks.

 

[DLC86]

Finally my new DMM was delivered so I measured my FM9 input. Feeding it a 1kHz sine wave at 1V rms I read -15.3 dBFS on the DI usb input, so that's what Fractal use as a reference voltage for their models, 6 dB lower than helix.

 

[pipelineaudio]

Finally my new DMM was delivered

which did you get?

 

[DieSchmalle]

I measured my HX Stomp input today and got -15.1dB using the AxeFX's synth block for signal generation (which puts out a 0.775V aka 0dBu signal at default levels btw) and double checked with two multimeters.

 

[James Freeman]

I measured my HX Stomp input today and got -15.1dB using the AxeFX's synth block for signal generation (which puts out a 0.775V aka 0dBu signal at default levels btw) and double checked with two multimeters.

Interesting.

I checked again just now.

Helix Floor (Pad Off, Guitar In-Z 1Meg):
-15.2dBFS with 0.500v input signal.
-12.2dBFS with 0.707v input signal.
-11.4dBFS with 0.775v input signal.

This time I'm running SPDIF output from the Helix into my DAW and seeing the dBFS values instead of using the Hard Gate, same results.
If you use the Stomp as a USB audio interface you can do the same.

I think @MirrorProfiles got the same results as me with his HX Stomp?

 

[MirrorProfiles]

Interesting.

I checked again just now.

Helix Floor (Pad Off, Guitar In-Z 1Meg):
-15.2dBFS with 0.500v input signal.
-12.2dBFS with 0.707v input signal.
-11.4dBFS with 0.775v input signal.

This time I'm running SPDIF output from the Helix into my DAW and seeing the dBFS values instead of using the Hard Gate, same results.
If you use the Stomp as a USB audio interface you can do the same.

I think @MirrorProfiles got the same results as me with his HX Stomp?

Yeah done it several times and it always matches your values

 

[DieSchmalle]

Interesting.

I checked again just now.

Helix Floor (Pad Off, Guitar In-Z 1Meg):
-15.2dBFS with 0.500v input signal.
-12.2dBFS with 0.707v input signal.
-11.4dBFS with 0.775v input signal.

This time I'm running SPDIF output from the Helix into my DAW and seeing the dBFS values instead of using the Hard Gate, same results.
If you use the Stomp as a USB audio interface you can do the same.

I think @MirrorProfiles got the same results as me with his HX Stomp?

Same via USB.
Hmm... I'm considering to sell it as a "rare extra hot HX Super Stomp" and get rich.