Helix LT / Level difference between live track and reamped track

[rizzy]

Hello there,

 

I'm new here - nice to meet y'all. I'm a soon to be 50 years old/new guitarist from Germany.

 

I'm trying to make a really great first impression by reporting a possible bug....

 

Kidding aside, I stumbled across the following issue:

 

I tried out the reamp possibilities on my Helix LT. During that, I discovered that the DI Signal which is send to the DAW via USB channels 7 + 8 is lower in level than the signal that is running through the processor while playing. I recorded a DI track from USB channel 7 and tracked the input from USB channels 1 + 2 at the same time. After that I added a track on which I recorded the reamped DI signal, this was sent to USB Channel 3 to the Helix LT through the same preset and settings. The reamped track is about 2 to 2.6 dB lower in level and lacks a little bit of high frequency content, it's not as 'crisp' as the recording of the 'live performance'.

 

This difference in level is enough to change the behaviour of the amp + effect models in a way that they start to sound different from what I'm hearing while I'm recording. I'd tend to think that the DI signal should be an exact copy of the signal that runs through the virtual circuits so that the sound of the two tracks would be the same.

 

Anybody else experienced this ?

 

 

Thx!

 

[phil_m]

4 minutes ago, rizzy said:

After that I added a track on which I recorded the reamped DI signal, this was sent to USB Channel 3 to the Helix LT through the same preset and settings. The reamped track is about 2 to 2.6 dB lower in level and lacks a little bit of high frequency content, it's not as 'crisp' as the recording of the 'live performance'.

 

I think the output from your DAW should be set to USB3/4. If you're only sending USB3, you could be getting only half the signal, which would be about a 3dB drop.

[rizzy]

Hey phil,

 

thank you for your reply.

 

I did some extensive testing meanwhile. It turned out that my initial test setting was flawed. I figured that the mentioned 2 to 2.6 dB level difference between the reamped and the live recorded track does only happen within that preset I was using. It differs from preset to preset, using one of my own presets delivered a difference up to 5 dB.

 

I had to take the amps + effects out of the equation, so that there was only input and output left. I then recorded a DI track from incoming USB channel 7 simultaneously with a track that captured the USB 1 output of the Helix LT. After that I reamped the DI track, sending it to USB 3 in of the Helix and tracking the USB 1 output again.

 

The DI track and the simultaneously recorded track were equal in level and tone, they both cancelled out when doing a null test.

 

The reamped track was equal in level but didn't cancel out with neither the DI nor the simultaneously recorded track doing a null test. This could be due to some modeling algorithm, but since there was nothing in the signal chain except for input and output, I'm not sure if that would make sense. It would make sense if at least an amp was involved and the nonlinearities are taken into consideration.

 

Result so far: Recorded DI and live track are the same, reamped track is somewhat in the ballpark of the others.

 

Here comes the interesting part. This result changes completely as soon as I try it with a preset/full signal chain. Comparing the live recorded signal with the reamped signal always shows that the reamped signal is a few dB lower in level.

 

You suggested sending the DI track via USB 3 + 4 instead of 3 to the Helix. That results in a level rise of the reamped track that puts it near the level of the live recorded track, but it still sounds different regarding reaction of the effects and amps to the guitar (distortion at heavier picking for example).

 

I always interpreted the parts of the manual where it says "send it to USB 3/4" as "send it to USB 3 or 4". I've been watching some videos regarding that topic on YouTube lately and all the guys (including the Line6 guy) where sending it to one USB channel only so I suppose that's the way it's intended to work.

 

As it seems, something is happening/not happening to a signal that goes via USB to the Helix LT. As soon as processing is involved (and I can't say which parts of the signal chain are responsible for it), it gets altered in a way that the reamped sound is lower in level and doesn't sound the same as the live signal. From a gut feeling I'd say that the level settings on the components of a signal chain are not computed or not computed in the right way if an USB signal enters the processor. This happens to all incoming USB signals, I tested it with channels 3 - 8.

 

I would love to make sure that I'm not missing something in my setup that causes this. It would be cool if someone could do a test and tell me if she/he experiences the same thing.

 

Just record a track with the DI out (input channel 7 on your DAW) and another one with the output of the Helix (Input channel 1 and/or 2 depending on if you record in mono or stereo) at the same time. After that, create a reamped track (use the just recorded DI track for that - set the output channel on the DI track at your DAW to 3 and the input at the Helix to USB 3/4 and record that output onto a new track, input comes from channel 1 and/or 2 again). Please check if the level of the reamped track is lower and/or sounds different than the live track you've been recording simultaneously with the DI track.

 

 

Thx! 

 

[rizzy]

Hey,

 

so, upon further research I found out that the USB channels sent to the Helix for reamping get attenuated by 6 dB once they enter a signal chain. The RMS values of the reamped tracks hover in the area about 5.7 to 5.9 dB in reference to the live recorded track, but I think that offset to the mentioned 6 dB might be due to the modeling algorithms.

 

This does only happen while using USB for reamping. The old school method - sending the signal from an audio interface (+ 4 dBu) into the Helix (input set to instrument) - works as it should, no level attenuation happening.

 

The via USB reamped track is not sample accurately placed in reference to a live recorded / DI track from the Helix. At 48 kHz sample rate it shows a negative latency of 91 samples or about 1.9 ms. I assume that the latency the Helix ASIO driver is reporting to the host is somewhat off.

 

Until these issues get adressed in one of the future firmware updates, the workaround would be to raise the level of the USB channel which is sent to the Helix for reamping by 6 dB using the fader or gain setting in a DAW. Another option would be to add a gain block to the Helix preset in question and and to raise the level by 6 dB.

 

If the reamped track should show up sample accurate in the DAW in reference to a live recorded track / DI track from the Helix, it has to be pushed by +91 samples or +1.9 ms. These values are only valid at a sample rate of 48 kHz. For any other sample rate they need to be recalculated accordingly.

 

I'm gonna add this issue to the bugs thread and will open a support ticket.

 

 

 

[Gary68]

Hi, I just saw this. This issue is also happening with the Helix Native. If I record a take on a DI track and on two 'live' tracks simultaneously from the Helix Floor's USB outputs and want to reamp the DI with Helix Native, I have to raise the level of the DI track by 6 dB to get the same output level that the Helix Floor delivers.

 

Gary

[rizzy]

Hey Gary,

 

interesting. Thx for pointing that out.