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[kristianjohnsen]

Hello.

I have recently read up on specialized DI-style products made to eliminate the need for microphones used to mic electric guitar amps.

For those that don't know what I'm talking about we're talking about products like this:

http://www.palmer-germany.com/en/mi/Products/Speaker-Simulators/Passive-DI-Box-for-Guitars-PDI09.htm

Basically, the idea is to drop the microphone and tap off of the amp output of the guitar amp/combo stack.  The DI is made to withstand significant voltage and turn that signal into a mic-level signal, but with a twist:  There are filters, etc, inside of the box that simulate what the amp speaker/cabinet does to the signal, so that what you get into your mixer is supposed to be similar to what you hear in front of the amp.

The idea is to make the setup 100% consistent, impossible to knock over, feedback-proof, etc.  The downside, of course, is that you miss out on exactly what the amp and cabinet is doing to the signal coming out of the power amp.  You do, however, get all the desired power stage artifacts.

Reading user reviews about these products it seems like the degree of success for users is often determined by what type of amp they are trying it with.  In other words, quite logically, the boxes' effect on the signal seems to be similar to that of certain amps - and if your amp's cabinet/speaker combo sounds kinda close to that, chances are you'll be happy with the results.

Anyway, all this got me to be curious about what these boxes actually do to a signal.  And further to the point:  What does some popular makes of speakers/cabinets do to a signal, and what about the speaker/cabinet/mic combo? 
There are plenty of more or less linear DI-boxes out there that can handle a high-level input.  So an interesting question for me is:  Can we use a box like this together with our channel strip processing on a digital mixer to replicate something similar to what's going on in the speaker/amp(/mic) combination?
I have a feeling that EQ, signal delay and dynamics can be done reasonably well and possibly better than with a cabinet simulator DI box.  I am unsure about phase shift, especially phase shift varying with frequency - but it would be cool to know what we're dealing with here.

Anybody care to run some measurements with a guitar amp - or a mic'ed guitar amp?

[John Roberts {JR}]

Designing a guitar amp baffle/cabinet, is closer to designing a musical instrument than electronic circuit. There are multiple moving parts, like loudspeaker break up modes, and sundry cabinet resonances.

Perhaps a DSP model could recreate a similar effect, which is kind of what the amp emulators do.

IMO no amount of static EQ, or simple delay/phase shift, will get you where you ask...

JR

[kristianjohnsen]

Designing a guitar amp baffle/cabinet, is closer to designing a musical instrument than electronic circuit. There are multiple moving parts, like loudspeaker break up modes, and sundry cabinet resonances.

Perhaps a DSP model could recreate a similar effect, which is kind of what the amp emulators do.

IMO no amount of static EQ, or simple delay/phase shift, will get you where you ask...

JR

I see your point and get the limitations. 

But considering what level of artists and techs seem to actually be fine with a simple box like what I linked to I'm thinking we can at least get as close or better with the level of channel strip processing available in mixers today.

[Nils Erickson]

My guess is that this would be better done without measurement, but simply with a guitarists ears (hopefully the artist you are working with)...  As a guitarist, I have yet to find anything like that remotely close to satisfying.  Furthermore, I feel like it is easy to get consistent results with a mic.  Feedback?  I don't think I have ever had the unintended kind with electric guitar.  Lastly, guitarists are a finicky bunch who love to obsess about the sound of their speaker and cabinet, for better or worse- why relieve them of that?

+1 to what JR said...

[kristianjohnsen]

My guess is that this would be better done without measurement, but simply with a guitarists ears (hopefully the artist you are working with)...  As a guitarist, I have yet to find anything like that remotely close to satisfying.  Furthermore, I feel like it is easy to get consistent results with a mic.  Feedback?  I don't think I have ever had the unintended kind with electric guitar.  Lastly, guitarists are a finicky bunch who love to obsess about the sound of their speaker and cabinet, for better or worse- why relieve them of that?

+1 to what JR said...

Just through coincidence somone started this thread on Soundforums.net just about at the same time as I started this one:

http://www.soundforums.net/live/threads/3333-Question-for-guitar-players

As you can see from the thread, well-known artists are apparantly using and being satsified by the cab simulator I linked to.  I ran a search of the product name in YouTube and was surprised by the level of artists and techs endorsing this thing.  I don't think it's all snake-oil, frankly.

Here's my take:

If you go to a big show to listen to a band and the venue is big enough that you're not really hearing the guitar amps on stage, you're hearing pretty much guitars through the PA only.  Chances are that guitar sound has been through a Shure SM57.  You know, the ultra-linear, super flat, highly recognized measurement microphone called Shure SM 57    Chances are, the guitar sound arriving at the mixing desk for mixdown will be closer to the original with a tap off the amp and a cab simulator, than with that super-accurate transducer called the Shure SM 57    No reason to fear the results of a side-by-side comparison through measurement is there?

If the results are reasonably close I'd be willing to try the method with the right type of guitarist.  I'm sure they'll protest soon enough if it's crap.

PS:  I have experienced feedback issues with electric guitar amp micing, but not typically with the usual pedal-to-the-medal rock guitarist, for sure.  It's a big world with many styles and musicians out there .

PPS:  What I certainly also have experienced is bleed from other amps or cymbals into open guitar cab mics.

[Patrick Tracy]

If you go to a big show to listen to a band and the venue is big enough that you're not really hearing the guitar amps on stage, you're hearing pretty much guitars through the PA only.  Chances are that guitar sound has been through a Shure SM57.  You know, the ultra-linear, super flat, highly recognized measurement microphone called Shure SM 57    Chances are, the guitar sound arriving at the mixing desk for mixdown will be closer to the original with a tap off the amp and a cab simulator, than with that super-accurate transducer called the Shure SM 57    No reason to fear the results of a side-by-side comparison through measurement is there?

Except that the SM57 is part of the sound, for better or worse, so bypassing it may be more "accurate" but isn't necessarily what the player wants or what sounds good.

[John Roberts {JR}]

Just through coincidence somone started this thread on Soundforums.net just about at the same time as I started this one:

http://www.soundforums.net/live/threads/3333-Question-for-guitar-players

As you can see from the thread, well-known artists are apparantly using and being satsified by the cab simulator I linked to.  I ran a search of the product name in YouTube and was surprised by the level of artists and techs endorsing this thing.  I don't think it's all snake-oil, frankly.

Here's my take:

If you go to a big show to listen to a band and the venue is big enough that you're not really hearing the guitar amps on stage, you're hearing pretty much guitars through the PA only.  Chances are that guitar sound has been through a Shure SM57.  You know, the ultra-linear, super flat, highly recognized measurement microphone called Shure SM 57    Chances are, the guitar sound arriving at the mixing desk for mixdown will be closer to the original with a tap off the amp and a cab simulator, than with that super-accurate transducer called the Shure SM 57    No reason to fear the results of a side-by-side comparison through measurement is there?

If the results are reasonably close I'd be willing to try the method with the right type of guitarist.  I'm sure they'll protest soon enough if it's crap.

PS:  I have experienced feedback issues with electric guitar amp micing, but not typically with the usual pedal-to-the-medal rock guitarist, for sure.  It's a big world with many styles and musicians out there .

PPS:  What I certainly also have experienced is bleed from other amps or cymbals into open guitar cab mics.

The load box DI can capture the part of the amp sound related to clipping and overload (a big part of tube amp sound), but not the speaker/box part, and surely not making the instrument feed back on purpose (like jimi). 

It may be an acceptable compromise for some professionals, because of the more consistent results when playing live in different venues with different stage acoustics. Just because it is acceptable to some doesn't make it ideal.

Another workable solution is put a real amp in a sound proof coffin off stage and mic that... This is even done by some recording studios.


JR

[kristianjohnsen]

Except that the SM57 is part of the sound, for better or worse, so bypassing it may be more "accurate" but isn't necessarily what the player wants or what sounds good.

How so?  If a guitar player is standing in front of his amp playing he's not hearing what the SM 57 is doing to the sound, anyway.

I'm interested in learning about different ways of making the PA reproduce what the guitar player is hearing more accurately.

[kristianjohnsen]

The load box DI can capture the part of the amp sound related to clipping and overload (a big part of tube amp sound), but not the speaker/box part, and surely not making the instrument feed back on purpose (like jimi). 


JR

Just to be clear, the speaker cabinet is still there, but the signal is tapped off of the power amp output.  If the player wants it to feed back between the guitar and the amp it still will.

It may be an acceptable compromise for some professionals, because of the more consistent results when playing live in different venues with different stage acoustics. Just because it is acceptable to some doesn't make it ideal.

Another workable solution is put a real amp in a sound proof coffin off stage and mic that... This is even done by some recording studios.


JR

It may be an acceptable compromise for some professionals, because of the more consistent results when playing live in different venues with different stage acoustics. Just because it is acceptable to some doesn't make it ideal.

Not saying it is ideal for everyone, but as long as products like the one I linked to is perfectly acceptable and desired by some, I would be interested to learn how I could emulate that performance with the tools already included in a mixer (when working with guitarists in that category).  Maybe it would be possible to have a library of settings emulating different cabinets, instead of using a box that just tries to copy one cabinet.

Another workable solution is put a real amp in a sound proof coffin off stage and mic that... This is even done by some recording studios.


JR

For most of the venues I work in the guitarists want to hear the cabinet on stage, I'm just interested in alternative ways to get what he is hearing into the PA.

PS:  One of the coolest setups I have seen was a US punk band I can't remember who was, who had foam-backed fake baffles in front of their real amps.  The backline looked semi-normal but stage levels must have been way down.

[Patrick Tracy]

How so?  If a guitar player is standing in front of his amp playing he's not hearing what the SM 57 is doing to the sound, anyway.

In some cases the amp sound may not be considered complete until it goes through a mic. Amps themselves started jut to make the guitar louder then became an integral part of the tone. Mic choice and placement have become integral to guitar sound. Of course starting with good amp tone doesn't hurt.

I'm interested in learning about different ways of making the PA reproduce what the guitar player is hearing more accurately.

I'm all for trying other things. I don't even own a Shure SM57. There are plenty of other ways to mic a guitar amp.

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