Line Out contains what ? Then into IR?

Mcentee2

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Bear with me if have misunderstood anything here!


I wanted to take my amp line out into a Mooer Radar (this is my own line out, not the built in SV20 SI that has cab sim on already), and it just got me thinking.

Following my testing on the attenuator thread it got me thinking about how Line Out and Impulse Responses work for recording etc

From what I understand, with a standard setup of a tube amp into a speaker, they both react to each other to varying degrees with frequency and levels.

At a simple level, the amp can change its freq/output at behaviour based on the rising impedance of the speaker. Thus is most obvious in the mid-high end or an amp driving a reactive load vs a resistive load.

The speaker takes that signal and makes a sound via its own response curves, resonances etc

The speaker may well have an idiosyncratic response back to the amp that then makes the amp work differently.

The amp could therefore react differently to different speakers?

So the signal output from the amp is somewhat dependant on the speaker it is seeing, to a greater or lesser extent based on amp design etc but in our world it is more likely than not.

So, we come to a Line Out tapped simply from the speaker jack, no cab sim etc applied.

This signal is basically the same as what is being sent to the real speaker, if you monitor it the only thing missing is the actual speaker responses as if you miked it that are probably high roll off and the bass resonance

*some* of that may be part of the feedback affecting the amp output you are monitoring (lower vs higher damping) but in general from a Line Out you are hearing the amp's "view" on things.

So, change the speaker, and you are probably changing what comes out of the amp.

I don't know how variable this is across amps/speakers, but I bet some amps/speaker combos make a huge difference and some don't.

Which brings me to Line Outs from amps feeding into an IR.

The IR represents a "speaker, cab, mic environment", I understand it is source independent ie you can apply it to any source - which I suppose is why they are useful!

Now, my question is that given the Line Out from an amp is dependant and somewhat governed by the real speaker attached (ie real load it sees) does this not make an IR based on another speaker somewhat "inaccurate" ?

Has anyone else cone up with why the above is or isn't a thing?
 
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ampmadscientist

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Bear with me if have misunderstood anything here!


I wanted to take my amp line out into a Mooer Radar (this is my own line out, not the built in SV20 SI that has cab sim on already), and it just got me thinking.

Following my testing on the attenuator thread it got me thinking about how Line Out and Impulse Responses work for recording etc

From what I understand, with a standard setup of a tube amp into a speaker, they both react to each other to varying degrees with frequency and levels.

At a simple level, the amp can change its freq/output at behaviour based on the rising impedance of the speaker.

The speaker takes that signal and makes a sound via its own response curves, resonances etc

The speaker may well have an idiosyncratic response back to the amp that then makes the amp work differently.

The amp could therefore react differently to different speakers.

So the signal output from the amp is somewhat dependant on the speaker it is seeing, to a greater or lesser extent based on amp design etc but in our world it is more likely than not.

So, we come to a Line Out tapped simply from the speaker jack, no cab sim etc applied.

This signal is basically the same as what is being sent to the real speaker, if you monitor it the only thing missing is the actual speaker responses as if you miked it that are probably high roll off and the bass resonance

*some* of that may be part of the feedback affecting the amp output you are monitoring (lower vs higher damping) but in general from a Line Out you are hearing the amp's "view" on things.

So, change the speaker, and you are probably changing what comes out of the amp.

I don't know how variable this is across amps/speakers, but I bet some amps/speaker combos make a huge difference and some don't.

Which brings me to Line Outs from amps feeding into an IR.

The IR represents a "speaker, cab, mic environment", I understand it is source independent ie you can apply it to any source - which I suppose is why they are useful!

Now, my question is that given the Line Out from an amp is dependant and somewhat governed by the real speaker attached (ie real load it sees) does this not make an IR based on another speaker somewhat "inaccurate" ?

If margins here are so small that make no difference then I can see it is worth accepting this.


Has anyone else cone up with why the above is or isn't a thing?


It does make it inaccurate but it changes the final sound (accurate or not).
Yes it is a variable but you may find that cranking the amp into a speaker and using a mic on the cabinet turns out with a sound that is preferable to the line out.
Or maybe using an iso-cabinet and a mic compared to the line out.
But the line out seems to have worked for clean but not very well for distortion compared to the mic and the speaker.
 

Mcentee2

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It does make it inaccurate but it changes the final sound (accurate or not).
Yes it is a variable but you may find that cranking the amp into a speaker and using a mic on the cabinet turns out with a sound that is preferable to the line out.
Or maybe using an iso-cabinet and a mic compared to the line out.
But the line out seems to have worked for clean but not very well for distortion compared to the mic and the speaker.

Hiya, that's for responding, It reads like you are referring to my results in the attenuator thread? Apologies if I have that wrong.

None of that work was really done with this thread's question in mind, more of an extension into hypothesis.

I am curious as to the "point" of an IR per se on any line out, where that line out content is already governed by an attached physical speaker :)

I suppose, for instance, if I am using my amp with its real G12H55, I can use the G12H55 IR to get a pretty good DAW representation.

But if I use the Creamback IR - well, the amp isn't connected to a Creamback, so the line Out will still be putting out a signal based on the amp/G12H55, and the IR just layers a Creamback/cab IR over the top.

If the two speakers are close enough to make no difference re amp response, then we are good to go.

I bet some (most?) speakers are radically different though re how the amp works with them (I don't just mean the miced sound they make!), and using IRs of those different speakers is not maintaining an accurate representation into the DAW if you don't have that physical speaker attached.
 
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ampmadscientist

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Hiya, that's for responding, It reads like you are referring to my results in the attenuator thread? Apologies if I have that wrong.

None of that work was really done with this thread's question in mind, more of an extension into hypothesis.

I am curious as to the "point" of an IR per se on any line out, where that line out content is already governed by an attached physical speaker :)

I suppose, for instance, if I am using my amp with its real G12H55, I can use the G12H55 IR to get a pretty good DAW representation.

But if I use the Creamback IR - well, the amp isn't connected to a Creamback, so the line Out will still be putting out a signal based on the amp/G12H55, and the IR just layers a Creamback/cab IR over the top.

If the two speakers are close enough to make no difference re amp response, then we are good to go.

I bet some (most?) speakers are radically different though re how the amp works with them (I don't just mean the miced sound they make!), and using IRs of those different speakers is not maintaining an accurate representation into the DAW if you don't have that physical speaker attached.

On some amps the line out is directly dependent on the speaker out.
But on others it's not at all, so it depends on which one.
I definitely understand what you are getting at. It's almost as if it would be better off as a studio monitor which is (closer to) accurate, compared to a guitar speaker.
 

Mcentee2

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Just found this great Sound on Sound article that expresses my point nicely.

https://www.soundonsound.com/reviews/boss-tube-amp-expander

It is an overview/review of the Boss Tube Amp Expander and nicely explains exactly what the resonance/presence controls do to allow you to mimic the load seen by the amp.

The Boss manual even has example settings to match "well known speakers/cab styles", this wouldn't be an option if it wasn't a real thing!

SoS then very neatly says this which precisely encapsulates/answers my question:

"The logical goal therefore is to match the settings to either the physical speaker that you've connected to the on-board power-amp output, or the virtual speaker whose IR you are using via the line output."

"What happens when you 'mismatch' the impedance curve setting ranges from the very subtle to 'something's not quite right'. To put this into some perspective, however, you can just set Resonance to L-Mid and Presence to H-Mid, or vice versa, and the majority of internal cabs and decent cab IRs will sound OK with some EQ tweaking. It's only when you want to make something quite specific sound as 'real' as possible, such as emulating a thunderous 'Dual Recto into a deep 4x12' perhaps, that absolutely optimising the impedance curve setting becomes crucial."

So mismatches can sound "bad", although in general "most" real speakers are all roughly the same from the impedance point of view. I

:)

That's it really, the amp needs to see the matching real load for the virtual speaker in an IR, for the IR to get you where you probably want to be :)

It might be 80% good enough, who knows.
 
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