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Tracking With Expensive Pre-Amps

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Tracking With Expensive Pre-Amps

Postby TBird » Mon Mar 05, 2018 4:16 pm

What is the point of using a (relatively) expensive pre-amp (with no digital output), eg DAV BG-2, when the (hopefully) excellent quality signal has to go through a second (presumably inferior) pre-amp on my audio interface (Focusrite Scarlett 18i20 - 1st gen) on its way to the computer? Or am I missing something?
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Re: Tracking With Expensive Pre-Amps

Postby Watchmaker » Mon Mar 05, 2018 4:47 pm

Depends on whether the Scarlett line ins go straight to the convertor. My quick googling didn't come up with a result but my guess is they don't. If you want to preserved that output, you'll need to go straight into some sort of AD, which the scarlett will accept via lightpipe if I'm not mistaken


*edit: added response*
or to be more precise - the benefits would be subjective, as in all things. I suspect the better pre would give clarity and perhaps harmonic content that a lesser pre might not. Whether (or how much) information gets lost going through a second pre is hard to say.

But great things have happened trying to work around limitations, so give it a shot and see how it sounds
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Re: Tracking With Expensive Pre-Amps

Postby Luke W » Mon Mar 05, 2018 4:54 pm

It shouldn't go through a second preamp. A preamp is used to bring a microphone signal up to line level, so the output should be connected to a line input on a converter/interface.

I may be wrong here, and I'm sure more detailed answers will follow, but I believe a lot of interfaces that have dual Mic/Line input channels still route the line signal through the preamp on those channels, but with a pad engaged to account for the level difference, which as you say, could negate any quality improvement you see from using a higher spec pre.

That said, the differences in preamps are almost always very subtle in most situations, and much less noticeable and critical than something like mic choice/placement.
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Re: Tracking With Expensive Pre-Amps

Postby CS70 » Mon Mar 05, 2018 6:19 pm

TBird wrote:What is the point of using a (relatively) expensive pre-amp (with no digital output), eg DAV BG-2, when the (hopefully) excellent quality signal has to go through a second (presumably inferior) pre-amp on my audio interface (Focusrite Scarlett 18i20 - 1st gen) on its way to the computer? Or am I missing something?

I guess the point would be the only one for which it's worth using the expensive preamp (other than rejoice in the glory of possession, that is): to drive it hard to get its distinctive coloration. That's because in "normal" drive conditions the preamp contribution to the sound is (so long you don't see the badge) all but inaudible, as the famous SOS shootout showed a few years back.

When it comes to whether the signal goes thru a stage of the preamp or not, Focusrite say something there https://support.focusrite.com/hc/en-gb/ ... ic-Preamps - according to them, it's pretty transparent. Also, most of the times the preamp is a one-time travel station for the signal - if you were going around hundreds of times (as it may happen with an insert effect) I'd may worry of some possible degradation, but for one go, there really shouldn't be anything to think of.
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Re: Tracking With Expensive Pre-Amps

Postby The Elf » Mon Mar 05, 2018 6:33 pm

I'm a great believer that qualities achieved earlier in the recording chain will make it to the end.
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Re: Tracking With Expensive Pre-Amps

Postby Commander » Mon Mar 05, 2018 7:28 pm

I use a DAV BG1 and I can tell you that it sounds tight, punchy, clean and fab. Don't waste time worrying about why it does, just do it!
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Re: Tracking With Expensive Pre-Amps

Postby ef37a » Tue Mar 06, 2018 12:10 pm

The vast majority of interfaces and mixers use the standard "10+10+10+10k +op amp" line input configuration and this will have a noise output not much better than -100dBu. Only the most carefully designed esoteric and expensive equipment will have better line ins than that and even there the limit due to 'physics' is about -118dBu.

Since a decent microphone amplifier (in an AI/mixer) will probably use THE SAME op amp plus a couple of discrete very low noise transistors, its noise output for comparable gain will be about the same. Stick a 20dB attenuator on the front end and feed it with 20dB more signal, i.e. the 'line' out of a pre amp and I doubt anyone could tell the difference?

This assumes of course that all the devices in the chain are linear and have a dead flat frequency response but there is no reason to think otherwise.

Of course, I am not suggesting peeps stuff Grace pres into 50quid Berry mixers but I would LOVE someone to do the tests and write it up for SoS! Might cause much the same chattering that the Great SoS Mic Pre (not!) Shootout did!

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Re: Tracking With Expensive Pre-Amps

Postby desmond » Tue Mar 06, 2018 1:28 pm

Commander wrote:Don't waste time worrying about why it does, just do it!

Welcome back! You've been missed... :wave:
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Re: Tracking With Expensive Pre-Amps

Postby James Perrett » Tue Mar 06, 2018 3:10 pm

ef37a wrote:The vast majority of interfaces and mixers use the standard "10+10+10+10k +op amp" line input configuration

Not sure where you get this from Dave, but just about all the circuit diagrams that I've seen include a pair of input transistors in both the line and mic configuration so the line input is attenuated and then amplified. The amplifier gain is usually less than that used with the mic input though. While this isn't usually a problem purists may want to avoid this.

The best solution is to find an interface with insert sends/returns. The insert returns will have the shortest route to the A/D convertor.
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Re: Tracking With Expensive Pre-Amps

Postby ef37a » Wed Mar 07, 2018 12:36 am

James Perrett wrote:
ef37a wrote:The vast majority of interfaces and mixers use the standard "10+10+10+10k +op amp" line input configuration

Not sure where you get this from Dave, but just about all the circuit diagrams that I've seen include a pair of input transistors in both the line and mic configuration so the line input is attenuated and then amplified. The amplifier gain is usually less than that used with the mic input though. While this isn't usually a problem purists may want to avoid this.

The best solution is to find an interface with insert sends/returns. The insert returns will have the shortest route to the A/D convertor.

I am not quite sure what you mean James? Do you mean that dedicated LINE inputs are mostly in fact hybrid BJTs and op amps? That is, as I said a common configuration for transformerless mic pre amps.

Yes, the insert will bypass the mic pre amp but all that should contribute is a bit of noise and it is likely that the signal to noise ratio of the 'boutique' pre amp will be comparable, even a bit worse?

It is of course bad practice to attenuate a signal and then amplify it again but much depends upon the specific circumstances and the relative distributions of the gains throughout the path as to whether the signal is compromised...It SEEMS a bad thing to do but has anyone ever tested it in practice? Then, inserts? They will be at mixer or AI internal level, not line level and so some attenuation will be needed anyway.

The virtual earth mixer 'attenuates' signals to buggerall but we seem to keep using the signals that emerge from the chips!

Please note, I am simply talking about noise levels and by inference, signal handling. I am not treading on any toes regarding people's subjective impressions of their precious pres!

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Re: Tracking With Expensive Pre-Amps

Postby Zukan » Wed Mar 07, 2018 9:39 am

Your signal path is as good as the weakest link.

Old Armenian producer on drugs saying.
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Re: Tracking With Expensive Pre-Amps

Postby ef37a » Wed Mar 07, 2018 10:19 am

Zukan wrote:Your signal path is as good as the weakest link.

Old Armenian producer on drugs saying.

Very true but that weakest link is not NECESSARILY a very clean internal microphone amplifier with an attenuator on its front end.

G.I.G.O.

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Re: Tracking With Expensive Pre-Amps

Postby James Perrett » Wed Mar 07, 2018 3:37 pm

ef37a wrote:
James Perrett wrote:
ef37a wrote:The vast majority of interfaces and mixers use the standard "10+10+10+10k +op amp" line input configuration

Not sure where you get this from Dave, but just about all the circuit diagrams that I've seen include a pair of input transistors in both the line and mic configuration so the line input is attenuated and then amplified. The amplifier gain is usually less than that used with the mic input though. While this isn't usually a problem purists may want to avoid this.

The best solution is to find an interface with insert sends/returns. The insert returns will have the shortest route to the A/D convertor.

I am not quite sure what you mean James? Do you mean that dedicated LINE inputs are mostly in fact hybrid BJTs and op amps? That is, as I said a common configuration for transformerless mic pre amps.

What I'm trying to say is that most interfaces don't have dedicated line inputs. Their line inputs share the active electronics with the corresponding mic input in exactly the same way as is done on most mixing desks (apart from the really high end ones with properly dedicated line inputs).

I'd agree that this is unlikely to be the biggest problem with most set-ups but it may worry the absolute purists (who are exactly the sort of people that use boutique mic preamps).
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Re: Tracking With Expensive Pre-Amps

Postby Matt Houghton » Wed Mar 07, 2018 4:03 pm

There are various reasons you might want to choose different preamps than the ones on an audio interface.

First, some offer facilities that many audio interfaces don't — eg input impedance options, and physical controls on every channel for 48v phantom polarity inversion, HPF and so on.

Some also offer the ability to 'drive' transformers and attenuate the output signal accordingly — a means of achieving distortion/saturation. Quite apart from the actual sound of that compares with plugins, applying it on the way in gets one more decision out of the way that you don't have to make later.

And, of course, if you also plan on using EQ or compression on the way in (another decision largely out of the way, leaving you less to do in the box), then you're going to need a mic preamp before those — which inevitably means before the mic preamp on the interface. And if you need one, it might as well be a decent one that you can use in other situations as required.

Some offer different amounts of clean gain (eg. for passive ribbons) or a different gain range. And another facility that's lacking on almost all interfaces (though a couple of fancier ones have remote-controlled preamp gain) is switched gain controls. Since you mention the DAV BG2, this has four channels of switched gain — this makes precise matching of channels easy compared with a budget interface, and can be useful for example for use with multiple-mic arrays.

Still more offer a nicer-sounding instrument input.

So, while there's undoubtedly a lot of BS spouted about preamps having mythical sought-after sounds (much of it rooted in confirmation bias), external preamps can still be very useful — even before you consider the purist question about whether your interface has dedicated line inputs or uses the mic amp circuit.
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Re: Tracking With Expensive Pre-Amps

Postby Urthlupe » Thu Mar 08, 2018 2:12 am

James Perrett wrote: I'd agree that this is unlikely to be the biggest problem with most set-ups but it may worry the absolute purists (who are exactly the sort of people that use boutique mic preamps).

Sorry James, but for me this is just wrong.... cards on table.... I have here a couple of Neve 8801’s, a pair of RND Portico 2 Channelstrips, the 1073 DPX, a pair of Neve ‘Classic’ 1081’s, a good number of the Audients mentioned and others.

I’m no absolute purist.... (there’s a Massive Passive in the rack, but I regularly use UA’s plugin - although on a cold winters day it doesn’t warm the room as effectively :-) ).

The idea that these devices represent a pinnacle of fidelity (or that their users seek a sonic ‘purity’) is bonkers - and let’s be honest, we all know there are generally much more significant elements in the signal chain. They are just tools, screwdrivers and spanners - if you like their functions, their sonic character, durability and build quality (Neve 8801’s excepted!!!), and feel they’ll suit your workflow, then you give it a go. Buy with care and if it doesn’t work out then you may well get your money back!

For me, Elf and Matt have it spot on.

And for the original poster (who has absented incidentally, leaving us old buggers to flap our gums at each other), I patch them in a number of ways including both directly to AI and via a mixer - I’ve never noticed any difference..... guess I really should A/B (and remove the badges) :beamup:

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Re: Tracking With Expensive Pre-Amps

Postby Hugh Robjohns » Thu Mar 08, 2018 11:15 am

TBird wrote:What is the point of using a (relatively) expensive pre-amp (with no digital output), eg DAV BG-2, when the (hopefully) excellent quality signal has to go through a second (presumably inferior) pre-amp on my audio interface (Focusrite Scarlett 18i20 - 1st gen) on its way to the computer?

People use 'expensive' preamps for various reasons. It might be just because they are expensive and having them in the rack makes them feel good. In which case the sound quality won't really matter anyway! ;-) It might be because the like the sound character a particular preamp brings, particularly when deliberately overdriven a bit. If that's the case, the sound character will be retained almost regardless of the signal path .

As for the 'inferior preamp' you actually have to look far and wide these days to find a genuinely 'inferior preamp'. As our blind preamp shoot-out proved quite comprehensively a few years ago, when handling signals with sensible headroom margins it's actually extremely difficult bordering on impossible to tell any difference between budget and super-expensive.

So yes, technically passing a signal from one preamp through a second preamp stage isn't the ideal way of doing things, but in practice the noise and distortion that might be added as a result will be negligible and way, way, way below the noise already captured in the original preamp's output... and since the preamp is being used for some 'colour', who's going to notice another 0.001% THD being slipped in.

So the Commander (Gold bless him -- welcome back!) is absolutely spot on. Don't over think this... just plug it in and get on with it!

H
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Re: Tracking With Expensive Pre-Amps

Postby Hugh Robjohns » Thu Mar 08, 2018 11:22 am

Luke W wrote:It shouldn't go through a second preamp. A preamp is used to bring a microphone signal up to line level, so the output should be connected to a line input on a converter/interface.

Well, technically, yes, you're quite right... and some interfaces do have dedicated line-only inputs. But an awful lot only have shared mic/line inputs and in the vast majority of case the line input is just an attenuator that knocks the signal down before passing it through the mic preamp operating with a modest gain. This is pretty much standard practice these days, mostly because it's cheaper than providing a second dedicated line input buffer -- but the manufacturers wouldn't get away with it if it introduced noticeable loss of quality....

In theory, attenuating a line signal only to amplify it again is nonsensical, but in practice it works perfectly well and whatever the theoretical signal degradation, it turns out to be a completely insignificant issue in practice, both in terms of noise and distortion.

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Re: Tracking With Expensive Pre-Amps

Postby ef37a » Thu Mar 08, 2018 12:08 pm

Thank you Hugh.
If I might make a crude analogy ? (well, digital actually!)

We all know that 24 bits is "superior" to 16 bits but in the real world 16 bits is actually more than enough dynamic range to reproduce practically any musical event. We use 24 bits for recording because it makes life much easier, we can keep levels well below digital clipping and the noise floor is wholly defined by the analogue noise at the input. This is a luxury they would have killed for 40 years or so ago.

So, Best Practice, super duper pre into a dedicated line input (and the very best I have found is the Self 12chip SMT variant which has a unity gain noise output of -118dBu) but into the vast majority of attenuated mic pre/line inputs you are never going to tell. Just as, 99% of the time the noise floor of your signal has already been defined BEFORE it hits the "grotty" 16 bit converter.

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Re: Tracking With Expensive Pre-Amps

Postby Luke W » Thu Mar 08, 2018 1:06 pm

Hugh Robjohns wrote:Well, technically, yes, you're quite right... and some interfaces do have dedicated line-only inputs. But an awful lot only have shared mic/line inputs and in the vast majority of case the line input is just an attenuator that knocks the signal down before passing it through the mic preamp operating with a modest gain.

I did think that was the case, thanks for clarifying. :thumbup:

I was thinking purely along the lines of using as clean a preamp as possible. What I overlooked is that a lot of the time, people will be choosing preamps with the intention of driving them a bit harder to add some distortion anyway.
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Re: Tracking With Expensive Pre-Amps

Postby blinddrew » Thu Mar 08, 2018 6:13 pm

Hugh Robjohns wrote:Well, technically, yes, you're quite right... and some interfaces do have dedicated line-only inputs. But an awful lot only have shared mic/line inputs and in the vast majority of case the line input is just an attenuator that knocks the signal down before passing it through the mic preamp operating with a modest gain. This is pretty much standard practice these days, mostly because it's cheaper than providing a second dedicated line input buffer -- but the manufacturers wouldn't get away with it if it introduced noticeable loss of quality....
Quick question on this bit if I may? (that wasn't the question by the way)
What about interfaces that have X number of mic inputs PLUS Y number of line inputs? Presumably it's only the mic/combi inputs that have the step-down-step-up rather than any of the line-specific inputs?
I'm thinking devices like Focusrite Scarletts or Tascam US series stuff.
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