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How to Make Sense out of the Mic Preamp Jungle
Cross the Threshold to Greater Sound Quality
As you learn about the recording arts you will find that the topic of the microphone preamp (mic pre) comes up over and over again. A mic pre is a preamplifier for the weak signals that come from microphones. The preamplifier boosts the signal to a standard line level, which all recorders can capture. How to hook up a preamp? Simple. Every stand alone preamp has a line level output, to which you connect to the line level input of your mixer or audio interface. Yes its that simple. "Aha!", you say, "I can just get the first $150 preamp and connect up and I'm up flying in the clouds of sound quality!!!!!" "YESSSS!!!"
Erm, dude. not quite. We appreciate your enthusiasm though! You know, dudes that take this "little leap" end up like this:
"So Dudely, how's that new Preamp?
"So Can U tell the difference?"
"Oh, its hard to tell sometimes, but the gain knob is MUCH smoother and its got a meter"
"What this button called 'CMP'?"
"That's a Compressor, it sorta makes things louder"
"But doesn't that add noise?"
"yeah, kinda, I think..."
Meanwhile, back on the "other side" of the threshold of quality, you'll witness recording professionals fuel a debate over which preamp is good to have for a particular situation. Notice I did not say "best". The true audio pros know that there is no universal best. Opinions are important in this area because few people have used all the preamps available. Funny, they never mention the $150 preamp Dudely bought.
So you think, I know, I'll try them out. But in a typical music store, they are not going to let you test 10 different models and even if they did, you'll have much trouble setting up a controlled environment in which to evaluate them. So should you go with what the pro's say? You can't afford 5 premium preamps. Maybe if you save you can get just one. These guys have used extremely high end preamps and their reference to quality may be to something you have never heard coming out of your speakers. They have heard it. You have not. You are going to have to make a "leap of faith" to get there, and unlike the "little leap" above, you have to make a "big leap".
Let there be no doubt that with the Mic pre you pay for sound quality. That is what the whole game is about! But the preamp alone is not wholly responsible for quality, it is just one component. Your a\d converters, the cleanliness of your signal paths, the acoustic properties of your recording room, your choice of microphone and choice of monitors (so you can hear the fine differences) are all critical to quality. Those who want "the best" sound quality might spend $4,000 on preamps, $3500 on converters, $1500 on an audio interface and $5,000 on mics and $3,000 on room treatment. That's $17,000 just to get into the pro ballpark, still far from "the best", and we haven't included the cost of monitors, DAW, software or cables. So my first bit of advice is to scale your choices to your overall budget. In other words...
How to get Good Quality without a Great preamp
Face reality. If you are just starting out and have a $1000 budget for everything, you should use the preamps on your mixer or audio interface and choose your Mic carefully. Do you have to then settle for crappy sound? No! Let's consider technique. You can get surprising results out of mediocre preamps and typical consumer interface preamps by meticulously setting the gain or trim level till its perfect, keeping a clean signal path, training your vocalist to use good microphone techniques and doing what you can to reduce your room reflections. A poorly set level on a great preamp recorded in a nasty reflective room will not sound good. Never rush the take. Take the time to move the microphone at a slight angle so the vocalist is not breathing directly on the diaphragm. Listen for pops and plosives and excess sibilance. Adjust the pop filter. Play with the proximity effect, see if you want it or don't want it and adjust the distance of the vocalists lips from the mic. (More distance if you don't want the bass boost). Try a different mic if you aren't hearing what you want. If the vocal is distorting, click in a pad if the Mic has one or switch to a dynamic Mic if you are using a condenser. If it just sounds too dull (which is common with audio interface preamps) move to a condenser from a dynamic. If there is too much preamp noise (hiss) turn down the gain and get the vocalist another inch closer. If there is too much background noise, kick yo homies out of the room, shut the door, close the window, toss a blanket over the computer, find the one place in the room where the voice sounds great without a microphone and put the mic right there. These are the ways you can get great sound on a budget--by being exacting, patient, persistent and doing tiny little things that improve the quality a tiny bit. You add them up and you have a better track.
The point is, if you want to sound like a pro, work like a pro, and then, after much deliberation, saving money, weighing options, get your preamp. Don't scrimp. Remember I told you several pages back I'll tell you where you can compromise and where you can't? The preamp is a piece of gear where you should not compromise. Get one you are convinced will give you better sound quality.
Taking the Plunge
It takes about $500 to get a dual preamp (and about $300 for a single) that is definitely and noticeably better than the "average" preamps on audio interfaces and mixers. That is my opinion, referenced from my own dual FMR RNP, my mono Great River ME-1NV, around 7 or 8 mixers with preamps, and about as many audio interfaces. You know, this area is so subjective its like religion, but I will tell you, that once you have heard the difference in your own studio, you know this, like it is an indisputable fact. There is a threshold to high quality sound. My goal is to get you over this threshold. Until you are ready to pop for at least that much ($300 for a single), don't fret about preamps. Also, don't think that any preamp over $300 is going to do. Really the cutoff point is closer to $1000, there's just a few preamps that have managed to do it under that. The FMR Really Nice preamp the "RNP", (which is a dual preamp), Grace 101, and i am considering adding Golden Age Pre 73 (which is a single preamp, highly regarded on our forums, which I will try soon!). You'll find these in pro studios and even though they cost less that the highest priced preamps, they are often held with high regard. Why? Once you get over that threshold of quality, its a matter of whether you like the "color", i.e., the texture, how pleasantly it distorts and yields pleasing harmonics when pushed. But the real good stuff is between 1-3k. I know that price hurts. It hurts Everyone. If there was a $150 preamp that sounded like a pro preamp, all the professionals would have 10 of them. Like I said, buying a great preamp takes a big leap of faith. I've taken you to the cliff, now you have to jump.
You may realize several times--you are Not Ready for this plunge. OK, we understand. Just work on your audio skills. Huh? Again, position the mic better, use a pop filter, set a better useable level, position the monitors better, improve the vocalist's techniques, fix the room with whatever you have to fix it with, learn how to mix a vocal so it stays above the band, learn compression, applying eq, reverb, sends, returns. In a word, experiment. This approach will give you much more sound quality than replacing one mediocre preamp with another. In a way, you guys that can't afford a great preamp now are blessed.
Why do I say that?! When you finally DO get that preamp after working on all these skills, you'll be blown away by your own sound quality. And yep, you'll cross the threshold and you'll know it. Unlike Dudely at the top saying "it's hard to tell", you'll be on a totally different audio landscape where the difference is clear and obvious. You paid, not only with your money but with your time. The gate opens. You are in. Welcome! :)
OK! I am off my soapbox on mic preamps. Lets talk about the types and features of preamps now.
Features of Mic Preamps
Some of the most expensive preamps follow the philosophy of "wire plus gain", which means there are no fancy add-ons, just phantom power, amplifying the signal and that's it!
Others add everything imaginable, such as compressors, peak-stop limiters, de-essers, eq and an array of filters, scoopers, harmonics shifters, s/pdif and ADAT digital i/o, all the way to including digital models of other preamps. I'm going to try to help you sort this stuff out.
Applying gain to the microphone signal is the main job that the preamp does. Ideally, the preamp amplifies the signal and does not add any additional noise or hum of its own. The tell-tale sign of a poor preamp is that you hear lots of internal hiss as you raise the gain all the way up to 60db. You turn up a hi quality preamp the same amount and the hiss is very faint, you can barely hear it. Everything is loud and crystal clear. That is what we want.
A problem with many mixer preamps is that hum can creep into the recording bus from other equipment connected to the mixer. That is why the best preamps are not on mixers. A good, stand alone preamp will amplify all sorts of sounds coming in from the mic which may be noisy, such as air conditioning vents, your refrigerator in the kitchen, traffic noise a block away, and breathing in the room but won't add any more noise problems. While the poor preamp often buries these low level sounds in hiss (and just lowers the quality of everything going through it), a good preamp exposes environmental problems and allows you to fix some of them. You might find yourself moving the mic away from the vents, closing the kitchen door, telling the vocalist to move their head slightly to the side, turning off the guitarist's buzzing amp, throwing a blanket over the computer. See, you can use the quietness of a great preamp to diagnose and fix problems before hitting the record button. This is one way a great preamp can improve your recordings. Its like you suddenly turned off that buzzing in your brain and can now hear things as they are.
This is a feature sometimes found on premium preamps that lets
you adjust the electrical impedance of the preamp. Nearly all preamps have
a high impedance and low impedance setting (HiZ is used for guitars and some 1/4"
mics, while LoZ Mics usually have XLR connectors). The variable impedance
feature gives you a range of settings, which may be useful for getting a different
response out of your mics. How important is it? The bigger your mic collection,
the more you may want this feature.
Class "A" preamps
You will probably notice many references to "Class A" preamps
in product literature, but no references to what this means. Heh, there is
not a government agency certifying grades of preamps, like Grade A milk, lol.
A Class A preamp is distinguished by its circuit design. In a Class A design
current flows all the time, as opposed to Class B or Class AB. A Class A preamp
will draw more current and run hotter, hence you'll see the preamp often in big
2 or even 3 rack space enclosures. While not as electrically efficient, they
tend to have more detail sonically. It makes a great buzzword too for manufacturer's
marketing departments, who use the term to denote the superiority of their product.
For a more technical description, check out
this forum thread.
Its not a shadowy rapper, not a slogan by Roland to sell Fantoms.
It is an "invisible" way to power condenser microphones with no extra cables or
wall plugs. If you use condenser mics, you need phantom power. And if your
preamp is worth anything at all, you already have it. Phantom power
comes from the preamp itself. It sends a small current to the mic right down
the XLR (mic) cable. Dynamic mics do not need phantom power typically.
Nor do mics with batteries (the battery supplies the power). The common spec
for phantom power is +48v. Inexpensive preamps may only offer +30v, and some
condenser mics might not perform optimally. So watch out for that.
Monitoring and the zero-latency headphone cue mix
Some preamps offer a monitoring signal chain that is separate from the main outs. We all need to give the performer some headphones so they can hear what they are laying down. Who needs monitoring features on a preamp? If you have a big mixer with multiple busses that can be routed to headphones, you don't. If you have a well-endowed audio interface that allows you to set up a monitor mix, or cue mix, custom tailored for the performer and routed to its onboard headphones, you don't need monitoring on the preamp either. You can usually create a cue mix in your sequencer. However, those going mixerless and who have audio interfaces that have limited i/o may need monitoring on the preamp. Why?
Monitoring the signal being recorded after it goes through the
audio interface and CPU can add latency. The acoustic guitarist might hear a strummed
chord slightly later than they played it. Even a small delay can confuse a
performer's sense of timing. You might hear about "zero latency" monitoring.
The zero latency monitoring feature will take a feed from the audio interface and
mix it in with the direct signal off the preamp, before it goes through the audio
interface and cpu. allowing for a tighter performance. Some preamps with this
feature may have a send and return for an effects processor so the vocalist, for
example, can hear their voice with reverb, something which gives them a little more
confidence. You might want monitoring features on the preamp because it is
Number of preamps
Preamps come in different formats. Some have simply one single mono preamp in the box. People who record only 1 track at a time don't always realize that even with just ONE mono preamp of quality you can sound tremendously better. There are also units with dual preamps, which are effective for recording with 2 mics in stereo. There are also units with four and even eight preamps in one box. How many you need, of course, depends on what you are recording. Vocals are usually recorded in mono, while acoustic guitars are sometimes recorded in stereo. Recording a drum kit requires at least 3 preamps and some use a lot more. Recording a whole band at once might require one for each member's vocal, one for their amps and several for drums. It does make a lot of sense to have one great preamp for vocals and a good stereo preamp. If you are on a strict budget, consider the 2 channel preamp first, as you can use just one side of it in mono for your vocal and still have stereo capability.
By no means should you consider that because a preamp that has a/d converters it is sonically superior. The classic "wire plus gain" preamp design is analog in, analog out with no digital signal path. More and more, though, as time marches on, a\d converters are being added to mic preamps. The true benefit of digital outputs on the preamp is that you can bypass the a\d going into the audio interface. Your digital signal, after it leaves the preamp, stays digital all the way to the storage medium. Can you tell the difference? Depends. If your soundcard has inferior converters, they are best to be bypassed whenever possible. Of course, if your monitors do not let you hear fine details, you'll probably not hear much difference.
To state it in different terms, it only makes sense, sonically,
to use a digital out on a preamp if it's converters are better sounding than the
ones on your audio interface. If you bit the bullet and bought $4,000
stand alone converters you'd be a bit daft to bypass them in favor of inferior converters
on the preamp. The only exceptions are matters of convenience or if the preamp
has some form of digital processing inside. If the signal is being converted
to digital inside the box, then bypassing the d\a out of the preamp and the a\d
into the audio interface is a good thing. In terms of convenience, in the
multi-channel preamp, you may see an ADAT option, which can send up to 8 amplified
mics at once bypassing, yep, 8 converters on the audio interface. It can be convenient
to have one thin lightpipe cable instead of 8 fat XLRs connecting the preamps to
the audio interface. Or if you have an audio interface with an unused ADAT
input, it makes a lot of sense to add an 8 channel preamp with ADAT output.
Onboard compressors, EQs, de-essers, limiters and gates
Do you need these extra features on your preamp? Many say no. And most of them are professionals. But I urge you to examine this question for yourself and your studio environment. Those with a professional studio room that is pristinely quiet with a large selection of mics and outboard processors truly don't need these items. The homeys in their converted bedrooms with only one mic an no outboard processors may benefit greatly from them.
With 24 bit recording, there is more "room" for recording an audio signal. Compression or limiting may not be necessary going in as it can be effectively added later by software, and many software compressors do a better and more accurate job later in the mix. Once you compress going in you are stuck with it. There is no "undo" after hardware compression. However, when recording live to 16 bit media, the equation changes. There is less headroom in a 16 bit system and if you record your level too low you will have to amplify the system noise to bring up the level during a mix. A little compression before hitting the recorder can give you an optimally leveled track. If you record to analog cassette tape a compressor is practically required to get a decent track. Recording live shows or field recording also benefit from compression as you can never control for abrupt volume changes that can go through the roof. Finally, some instruments are so peaky by nature you know you want compression to even out the signal. Acoustic guitars and drums fall into this category, even when recording at 24 bit.
Note that some preamps allow you to add an external compressor rather than supplying you with one onboard. In this case, on the back of the preamp there will be insert jacks. No inserts? You can also route the line out of the preamp to the line in of a compressor and feed the compressor output to a recorder. You can keep your signal balanced this way. With inserts, you are forced to go unbalanced.
A gate can be an effective tool. A gate will lower the signal automatically when it drops below a defined threshold. If you have a great, quiet room there is less or no need for a gate. But many of us do not have that perfect room in our home studios and have to contend with kids and birds screaming in the yard, hard drives grinding away, trucks going down the street and distant aircraft, all of which will be faithfully recorded if you have a nice mic and pre. A well-setup gate can dramatically improve the signal to noise ratio, providing the illusion of recording in a dead silent room. Poorly setup it can make a track sound unnatural, with the breathing of environmental noise coming in and going out. The true solution is to improve the room, but for those of us who cannot, the gate can improve a track immensely.
There are workarounds to having a gate. You can always "zero-out" data in your sequencer's audio editor with a silence command. This arguably, is superior to gating because with the mouse and screen at high zoom levels you can zero out noise with surgical precision.
A de-esser is a variable eq circuit which kicks in when a threshold of a certain focused frequency is reached. It is used to reduce sibilance, the "ess" and "shh" sounds that some vocalists cannot control. Often in a recording situation, it is better to try a different mic than turn on a de-esser. You might also position the vocalist slightly off axis to reduce these sounds. It is also possible to eq them out later or apply a software de-esser.
EQ, or using an equalizer on the source, is something that can usually be done later in the mix. Software equalizers are at a high state of the art. if you are recording live to direct to media feeds where there is no chance for post production, the EQ can save a recording.
Hi pass filtering (also called bass rolloff)
is important as many mics pick up an astounding amount of bass. You can do
this at the mic, on the preamp, or later in the mix but it is often better to attack
this problem at the source, the Mic. If the mic doesn't have a rolloff, then
the pre's rolloff can be used.
So now its back to you. What features do you need? You back through the article and make a list of the features you want and then go compare your list with the features on the preamps available. You should be able to identify exactly what you want, and hopefully you will find a product that suits your needs. OK, I hope i have helped you identify some issues that surround the selection of the ideal mic preamp for your studio. Indeed it is a major step towards improving your sound quality. I hope i have demonstrated that the preamp alone is not the solution, but simply one that puts excellent sound quality within our reach.
Best of Luck in your recordings!
Revised Jan 2010
Noobie Questions and Answers
Q) Tweak! Dude! This article is over my noobly head! I just want to be able to record a vocal using an XLR mic on my audiophile 2496. I have NO preamps right now.
A) Right! This article is geared towards those who already have the run-of-the-mill preamps and want to go a step further. In your situation you need to get some to get started. You can do this in various ways. A) Get a small mixer. There are plenty of Behringer, Mackie and Alesis mixers that will help you get going. B) Replace the 2496 with an audio interface that has some mic pres on it. C) Add an inexpensive Mic pre. One that i think has a lot of merit on the lower end is the MAudio DMP3 Dual Mic Pre and Direct Box Worthy. For the more budgetary constrained there is MAudio AudioBuddy and the ART Tube MP. There are other inexpensive preamps by ART, Behringer and others.
Q) I have a condenser electret mic that uses batteries. Do I need phantom power?
A) No. The batteries are powering the mic.
Q) I have a cheap mic that has a 1/4" TS plug on it. What preamp do i need?
A) That is probably a Hi-Z or Hi impedance mic. Preamps with "guitar" inputs
will work for Hi-Z mics. Hi-Z mics require less gain, but are often noisier.
Mics with XLR connectors (3-prong) are usually Lo-Z or Low impedance, which has
a weaker, cleaner signal.
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