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Hi-Z input and guitars

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Hi-Z input and guitars

Postby jellyjim » Mon Jul 29, 2019 2:09 pm

Hello

I understand that, in technical terms, a Hi-Z input is about impedance matching and in practical terms, a Hi-Z input stops an electric guitar sounding crud.

But even so, is it correct to say that a guitar recorded through a Hi-Z input is only ever a pre-cursor to re-amping, and in more recent years, amp modelling? The signal might have plenty more girth or body than if it were just plugged in to a line input but as it's been no where near an amp it lacks any real 'electric guitar-ness'.

I ask because I've just been recording a new guitar for the first time through my new Apollo Twin into UA's excellent Korg SDD3000 model and frankly it sounds fantastic before it's been anywhere near an amp model.

Is it a case of if sounds good it is good or, 'am I doing it worng?'

What's the history of recorded guitar sans amp? Is it a celebtrated one?
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Re: Hi-Z input and guitars

Postby Hugh Robjohns » Mon Jul 29, 2019 2:51 pm

jellyjim wrote:I understand that, in technical terms, a Hi-Z input is about impedance matching...

No, it isn't. There is no 'matching' going on int he case of an electric guitar. Impedance matching is a very specific condition which doesn't apply to plugging a guitar into an amp etc.

The high-impedance input is required to avoid 'loading' the guitar pickups, minimising the current flowing around the circuit and allowing the maximum possible output voltage to be developed.

... in practical terms, a Hi-Z input stops an electric guitar sounding crud.

Now that is a statement I can go with! ;-)

But even so, is it correct to say that a guitar recorded through a Hi-Z input is only ever a pre-cursor to re-amping, and in more recent years, amp modelling?

No, I wouldn't say it was correct. Plenty of commercial recordings have used unprocessed DI-d guitars (and the majority of bass recordings still use DI-s). But, a DI-d guitar can sound pretty flat, sterile and bright, so if a mic-able amp isn't available at the time, then some sort of subsequent re-amping or modelling is commonly used.

It should also be said that a lot of engineers will record a guitar DI alongside a miked-up amp as a 'just-in-case' backup, and it may well never actually get used!

Is it a case of if sounds good it is good or, 'am I doing it worng?'

I'm always happy to go with the 'if it sounds good...' approach! :-D And I don't see anything wrong in doing what you're doing if you like what it produces.

The usual complaint about DI'd guitars is the brightness. A typical guitar amp/speaker comb tends to have a fairly rapid roll-off above 4 - 5kHz or so which doesn't happen in a straight DI signal. But I suspect there is probably sufficient HF roll off in that Korg model to smooth things over nicely.

H
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Re: Hi-Z input and guitars

Postby Wonks » Mon Jul 29, 2019 2:58 pm

Well, it's less about impedance 'matching' and all about providing a high enough impedance so that the pickups don't get too 'loaded' and so loose all their high end signal. 500k will do, but 1 Meg is that bit better. You can go higher, but it stops making any real impact on the sound unless you have a straight piezo pickup (no pre-amp) where 10 meg is good for the best sound.

Look at the straight DI sound as a decent clean sound. There's absolutely no reason that you can't get a great sound just straight in (maybe with a bit or reverb added). Many hit records made, especially funk, with the guitar DI'd straight into a desk with no guitar amp in sight.

No distortion, so no extra high harmonics being created that make a non-speaker simulated sound very fizzy and unpleasant (it's more about the speaker sim than the amp sim here).

Of course, amp and speaker sims come into their own once you start dirtying up the guitar signal.
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Re: Hi-Z input and guitars

Postby Wonks » Mon Jul 29, 2019 3:04 pm

Guitar speakers don't have a roll-off in the way that a low-pass filter does. There is a pretty severe drop in output, typically from around 5kHz to 7kHz where there is a 20-25dB drop in total output by 7kHz - but then the output continues at that level. So you get some extra high-end from a guitar speaker that makes it sound that bit more interesting than if you just put a suitable low-pass filter on the guitar signal at 5kHz.
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Re: Hi-Z input and guitars

Postby Folderol » Mon Jul 29, 2019 3:13 pm

Another point is that a low impedance can change the way the pickups interact with each other and to some extent the strings themselves. Bear in mind that the strings are the energy source that creates the pickup current.
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