We all love making music and recording. It's a product of our soul. Who would want that product not to be as damn good as possible? It's only inevitable that, shortly after the amazement of having made our first (more or less) successful recording fades a little, a quest for "better quality" begins!
So off we go buying new equipment, replacing old stuff and adding bits and pieces (and the more expensive, the better, because everybody knows that you get what you pay for, right?), in a valiant attempt to get that mythical "professional" quality level which will finally bring our magnificent creations to the masses.
And sooner or later, any budding engineer will pose the ultimate question: do I need better preamps? Is it ok to use my console preamps, or interface preamps, or do I need to buy expensive "external" ones? And across consoles and interfaces, how do evaluate the quality of their preamps (beyond adopting someone else's opinion without knowing why?) If you have read the very first post in this blog ( "What makes a great recording?") you know that these days kit plays a quite small part in the overall quality of a recording. And preamps are quite down in the list.
However, let's assume you have perfected everything in your recording chain that comes before the microphone pre-amplifier. That is to say:
You perform like Elvis.
Your recording room sounds like Abbey Road Studio 2.
You have spent hours carefully positioning your lovely Neumann U67 in it.
If you're there - if you're really there - then your preamps are, indeed, the next thing to look at.
Should you plug the 67 in your $100 interface? Do you absolutely need that $2000 Neve preamp? Is that $5 interface good enough? Can you just plug your microphone in your computer mic input and be done with it? (flash preview: the answer to these two latter questions is no).
As always, turns out that the answer depends on what you want to do. Most often, the preamps you have are more than good enough and you should really save your money.
To find out why, the best point to start is by seeing what good preamp means.
Good preamplifiers are good amplifiers
A pre-amplifier sole function is to take a tiny weeny signal (the voltage differential produced by the microphone) and amplify to a more useable level ("line" level) for further processing.
As with any amplifier, a mic preamp is "good" if it has an usable gain range (i.e. it can amplify signals high enough for your needs), and if, when going thru it, a microphone signal is not changed in any other way than its amplitude is increased.
An ideal amplifier does just that: it raises the signal as much as you need, without adding noise or distortion.
As it happens, real-world amplifiers are not quite so perfect. They usually do, indeed, add a little noise and distortion, most often when operating near the edges of their performance envelope (aka when you crank 'em) but a little bit also in "normal" operating conditions.
Actually, the term "pre-amplifier" is used for amplifiers which are meant to do the job on very low voltage input signals (a "mic level" signal ranges between about 5 and 50 milliVolts), therefore requiring that their internal noise be very low (not to mess up an already very low signal).
So in general - let's repeat it - the less noise and distortion it adds, and the more the amp behaves consistently across all of its input voltage range, the better the amplifier is. It is more hi-fi.
So why are real world amplifiers less than perfect?
Well, imperfections are broadly the result of all the small differences between real-world physical components and their theoretical counterparts: a little component tolerance here and there, a little design compromise, the result of less than perfect mass-manufacturing processes and so on. The more time and attention is given to aspects such as these, the better (but more expensive) the result - in the sense of closer to the ideal.
Since a mic level signal is so low, avoiding noise and distortion when amplifying it is not trivial. In times pasts, it used to be that design and manufacturing compromises were a reason for big differences between very expensive, high quality, "professional" preamps and cheap, mass produced, "consumer" ones. The inexpensive ones were noisy, added distortion and in general were much poorer in amplifying the microphone signal without damaging it.
These days, however, innovations in both computer-aided design, testing, and computer-driven manufacturing, high volume productions, efficient supply chains and so on, have increased immensely the level of quality that is possible without high costs.
While of course there are still a few manufactures that sell cra.. pardon, less than good equipment, in general the result of such innovations is that even run of the mill interfaces and mixers nowadays have amplifiers that,will add very little noise and very little distortion when used within their design parameters.
They also tend to have a reasonable clean gain range (with gain, the rule is "the more, the merrier"): average interface preamps will give you some 55-60 dB of clean gain, because that is what the current single-chip op-amp technology can achieve easily and well (beyond that, the risk of electronic instability increases and the circuitry design and components tolerance needs to be tighter, more complex and expensive).
Fact is, 60 dB of gain is usually plenty enough. It may be not enough only in cases relatively uncommon for the home studio: say you're using passive ribbon mics or need to record faraway sources (classical recordists do that for example).
All in all, we can well say that, by using a regular interface/mixer preamp, you can still nail that Michael Jackson vocal... but you may need something a little more powerful for capturing Cage's 4′33″ in all its (quiet) splendor.
In other words: the answer to "are modern interface- and mixer- preamps good?" is in most cases "yes, they're are pretty good".
Very hi-fi and transparent, and with reasonable gain range for many applications.
All this means that, assuming you know what you are doing (i.e. your gain staging is good, and you work with good headroom) almost any modern preamp will do a quite good job: your stellar performance in a great room with a great microphone in the perfect location will be captured in all its high fidelity awesomeness.
Good preamps are also good to use
There are, of course, more aspects to amplifier performance than transparency and amount of gain.
They tend to be of the practical sort. For example, the overall functionality of the controls, their quality and durability can be important: "pro" equipment very often is not necessarily functionally better but simply more durable, and fixable if it breaks.
For example with the preamp gain controls, cheaper gain knobs are sometimes small, fiddly and more prone to breaking after extensive use; they also tend to behave non linearly, with most of the gain concentrated on the last few degrees of movement, making it harder to fine-tune the gain than when you have a large, more linear control.
Worth noticing that while some audio interfaces still suffer from that, many modern ones have digital gain controls, which eliminate the problem entirely: the gain on my RME or Focusrite are digitally controlled, and they can be set with utmost accuracy from software.
When it come to being repairable, designs which use more modular approaches or simply have components that can be easily changed will be more expensive than otherwise, but less likely to become a total write off if they break. Whereas single-board surface-mounted "locked" designs may be much cheaper to manufacture, but when something goes wrong, it's often too impractical or expensive to repair them (someone should tell a certain producer of popular computers and phones, perhaps..).
As an aside: what about on-board microphone inputs and computer sound cards a-la-Soundblaster (as opposite to audio interfaces made for recording)? I will try and make a post specifically on that in the future, but for the moment suffice to say that, not being intended for music recording, they generally have far poorer performance in terms of preamplification and A/D conversion than even the cheapest audio interface. So don't go there.
Color and character
There is, however, one aspect that still distinguishes on-board interface preamps and good external ones. That's "color" (or "character"). Let's see what it means and how important it is in practice.
The point with "color" is that, sometimes, high fidelity is not what we want.
Just like a great microphone might not reproduce your voice with total fidelity, but make it sound better than what it is, a great preamp might not amplify your microphone signal with total transparency and fidelity, but rather color it.
Coloring is a shortcut for adding a little noise and distortion in a way such that the result is pleasant to the ears.. (..which makes it clear why we use a shortcut).
Does it mean that if you get yourself one of these (usually expensive) "character" preamps, your vocals will immediately be nicer and better (due to the preamp color)?
No, not necessarily.
Remember: now and in times past, most manufacturers of preamplifiers have in mind the definition of "good" = "transparent" when they design one. They try to get as close as they can get to ideal, transparent amplification, no matter which technology they employ.
Regardless on how much marketing blurb flies around, the fact is that even tube preamp designers go a very long way to ensure that their designs do not distort or add noise (it's just a little harder to do that with tubes than with solid state). That was true especially in that technology heyday, where tube preamps were carefully designed to be as transparent as possible.
That means that the better (and more expensive) the preamp, the cleaner it will be when used in its designed range.
And since - as we saw above - even inexpensive designs can be pretty good nowadays, the net effect is that will be very little difference in the sonics of a good external preamp and an interface one when used sensibly.
Let me repeat: when used sensibly, a $2000 preamp and a preamp on a (modern) $200 interface will yield pretty much the same sound quality, with marginal differences.
That means that it makes little sense to replace your on-board interface preamp if you you're gonna use it sensibly.
Used without overdriving it, the $2000 preamp won't likely color the signal a great deal, and therefore (pre)amplify in a similar, rather hi-fi, manner as an audio interface or mixer.
So how in the world we get our money's worth from a great preamp? How do we color the signal?
Easy: we use the preamp in a non-sensible way. That is to say, we intentionally push it outside its performance envelope.
Also called we crank the gain.
In broad terms, the difference between high end preamps and the ones mounted on your interface is that, when pushed, the former sound better, the second sound worse (or cannot be pushed at all).
There's a couple reasons for that.
One, the obvious: to color the signal in an useful manner, the preamp must continue to sound good when its headroom is exceeded and it starts distorting. Think of a good guitar amplifier: when you push the drive and get the preamp to distort, you obtain a sound that (when emitted by a guitar cabinet speaker, which is a special kind of very-much-not-hi-fi- speaker) is nice and rock'n'roll. The same applies for microphones: to "color" a vocal, we increase the gain so that, when the singer does his or her thing, the signal level goes beyond what the circuit can handle cleanly (it exceeds its headroom). The result is a little distortion - especially on the higher volume parts - but the resulting timbre is pleasant. Since we're operating outside the design performance envelope of the circuit, its response (aka the sound) will depend much more from the circuit design than when we are inside it (since within their design parameters, all circuits aim to do the same thing - transparent amplification). That's why different preamps color the signal in different manners. There will be quite a bit of noise added when doing so, but again great preamps add it "just so" even when a overdriven, resulting in a very mixable recording.
Two, after cranking the gain, there must be a way to bring it back down to a reasonable voltage level. That's because after cranking the result will be by definition be at the top of the amplifier's output range - way too high for whatever circuitry that follows, especially the A/D converters. We need essentially to de-gain the (already distorted) signal to get it back within the dynamic range of whatever A/D converter that follows. It will still be distorted (i.e. the waveform has been changed) but its amplitude will be in a range where the A/D converter works well. In concrete, a preamp that can be used for color will have two gain controls, one for cranking the gain, the other for output level (aka volume). So that we can get the timbre changes due to overdriving it, but preserving the correct gain staging. This is especially important when recording digitally, as overdriving the A/D converters is (in most circumstances) a recipe for sonic disaster.
So, to summarize, on-board interface preamps tend to be clean, transparent and without much character.
With some exceptions, they tend to sound not especially great when overdriven.
More to the point, they shouldn't be overdriven since there is usually no level control after them: the preamp stage goes directly to the A/D converters. And the A/D converters most definitely do not like (and cannot handle) signals which exceed their headroom - resulting either in digital overload (which sounds horrible) or much higher quantization errors (a "strained" sound).
Fill that questionnaire
To wrap it all - let's get back to the original questions: do you need new preamps?
Here's what you want to ask yourself to find out:
Have you already really fixed all the stuff that is more important?
Are you using your computer or gaming sound card preamps?
Is your interface really scraped at the bottom of the pile?
Do you hear any apparent noise and/or distortion in your recording (when you're recording sensible levels?)
Do you need more clean gain than your interface/mixer can provide for the kind of work you typically do?.
Are you going to use the preamp heavily (every day for hours), and need something that can withstand that kind of usage? And that can be more easily repaired if necessary?
Do you want to color the signal at preamp stage instead of mixdown?
And of course:
Do you want to be able to brag about your high end kit? :-)
So in the end, it's about your choice.
Most of the quality of what you do lies before the preamp anyways, so unless you're recording on into the computer mic-in... or really and often need more gain... or your current preamps are noisy or distorting (when used sensibly) or don't have precise enough gain controls... or you want to color your signal when recording rather than in post... you probably can stick with the interface/mixer preamps you have and spend your money in further improving your recording space instead... because it doesn't still sound like Abbey Road Studio 2, does it?
And, about coloring "in input": remember that color or character are just synonyms with changing (aka distorting) the waveform. It doesn't really matter much where that happens. These days, with 24 bit recordings and DAWs, we have processing capabilities so that you can record the signal perfectly clean and distort it later.
There's nothing holy in capturing an already distorted signal with respect to capturing a pristine one and distorting it after the fact.
It's really up to you and your working methods, workflow and subjective preference.
But, if you really want to change the timbre directly at recording time, and "print" it into the recording itself, you'll likely need an external preamp as your interface won't likely be able to both achieve distortion and maintain a good gain staging into the A/D converters.
Both are different ways to get the same result: a recording you like!