Recording (and live sound) Part 4 – Microphones
There’s a lot to say about microphones, and I’ll admit that there’s still a lot of mystery in them to me, as I don’t understand a lot of the technical stuff about how they work, but I have a pretty good understanding of why some are better than others in a given application, so I’m going to try to explain some of that here.
One of the first things to know is that a mic that sounds great in the studio is not necessarily the mic you want to use on stage, where you have to think about feedback and just plain being heard, especially as the nylon string guitar is a relatively quiet instrument, which is an issue if you’re sharing the stage with an orchestra or a drummer or flamenco dancers.
There are four types of mics you should know about (there are more than this, but these are the common ones): Tube condenser microphones, ribbon microphones, dynamic microphones and condenser microphones.
Tube mics and condenser mics both need external power to work (the capsule needs to be electrically charged, but you don’t really need to know this and I don’t quite understand it myself). In the case of a tube mic, you will have an external power supply, so the mic will plug in to the power supply (psu), and from the psu you plug into the preamp. A non-tube condenser (generally just called a condenser) requires phantom power, which is a 48 volt charge that is sent from the preamp to the microphone along the same cable used to send signal from the mic to the preamp (so signal travels one way and power travels the other way). Most preamps have phantom power, but there are also outboard 48v power supplies one can use if needed.
You’re not likely to find very many tube mics on stage (mainly because the psu’s make them less convenient, but also because they tend to be more expensive and fragile), but you’ll find plenty in studios. A brief history of the path from tube to solid-state condensers goes like this: Tubes were needed to power condenser mics, so that’s all there was. Solid state mics were invented and everyone said ‘hooray – now we don’t need those stupid power supplies anymore. Let’s replace those pesky tube mics with these great modern ones.’ There are stories (probably apocryphal) of radio stations literally throwing out their old U47s when solid state came out. And the first phantom powered mics to come out really were great – the Neumann KM84 was the very first one and it’s very much considered one of the all-time great mics. But with time people said ‘Hey – we miss the sound of those old tube mics’, so those old U47s that were supposedly getting thrown out now go for about $10,000 a pop.
What’s the difference between a tube condenser and a (non-tube) condenser? The most common answer is that tube mics are ‘warmer’. These words can very unsatisfying, I know. The science has something to do with how a tube distorts versus how a transistor does, with the former being regarded as ‘better’ or ‘smoother’ or whatever. This is where your ears come in. I should also mention that now that tubes are hip again everyone is making tube mics, and they’re not all great. Personally I would say that you should first get a great condenser mic, and later, when you’ve heard a few and know what they do you can decide if you even need a tube mic. Some of the most famous vintage tube mics are the AKG ‘ELAM’ 251 and C12 and the Neumann U47, U67, and KM54.
N.B. – You’ll find reference to the Telefunken U47 or ‘ELAM’ 251 or the Siemens C12, etc… The ‘ELAM’ mics and the C12 were made by AKG and the U47 by Neumann, but Telefunken, along with Siemens and Norelco were distributors, so you’ll find a lot of older tube mics (and some non-tube AKG mics) that are badged Telefunken, Siemens or Norelco, but these are not the manufacturers – a U47 is a U47 and made by Neumann regardless of the badge.
Condensers of the non-tube variety are probably the most common studio mics (after the Shure sm57, which we’ll get to). The most famous condenser mic around is the Neumann U87, which is a large diaphragm multi-pattern condenser (we’ll get to those terms in a minute, too) as is the AKG 414. To again use words that may or not mean anything to you, people might generally describe condensers as crisp or clean.
Condensers are more sensitive than dynamic or ribbon mics (in a minute), so it’s important to know that a condenser might be harder to control in terms of feedback on stage because of this sensitivity. That said, a good sound guy can usually take care of these things, while you on stage will not have such an easy time of it.
Dynamic mics don’t need any external power. They work like a loudspeaker in reverse – the sound waves move the diaphragm, which sends a signal down the cable (something about magnets and coils – again, I drive my car very well and know when a truck is more appropriate than a sportscar, but have no idea how internal combustion actually works).
Dynamic mics have a lot going for them – They are less fragile (so you can take them to gigs and not worry too much), they are less sensitive, which means you can get more gain before feedback, and they are generally less expensive. To make a very sweeping generalization, you could say that dynamics are better for live and condensers are better for studio, but there a tons and tons of cases where this will not be the case.
You may very well want to use dynamics in the studio on louder instruments, such as drums or horns, and on some voices certain dynamics have a kind of magic (Michael Jackson’s voice on ‘Thriller’ was recorded using a Shure SM7, which is generally regarded as a broadcast mic for radio).
There are a lot of great dynamic mics out there, including the Shure SM57 (which I mentioned in my last article) and SM58, the Sennheiser 421 and 441 and the Beyer M201, which I use for gigs.
If you picture the old RCA mics from the ‘40s that were almost as big as the anouncer’s head, those were ribbon mics, s called because they use a tiny ribbon of sort of corrugated-looking aluminum. Until recently, ribbon mics were the most fragile of the bunch, as that little ribbon could be broken pretty easily, but now some manufacturers are starting to make ribbon mics out of nanopolymers or somesuch and they are starting to seem like another flavor of condenser.
Ribbon mics are almost all bi-directional, which means they pick up sound from the front and back, but not the sides.
I don’t have as much experience with ribbon mics as I do with the other kinds, but in my limited experience I’d say that unless you’re recording your electric guitar’s amp or trying to make someone sound like Sinatra, they’re probably not your first choice. I’m sure people will take issue with this last statement, but unless you already have a lot of other flavors of mic, I’ll stand by it for general purposes.
Capsules and Polar Patterns:
The part of the mic that actually receives the signal is a little round disk (or a ribbon, of course) that either is or isn’t electrically charged (condenser vs. dynamic) and is called the diaphragm, and it is part of the capsule. Mics can have large diaphragm capsules or small diaphragm capsules (there are some medium, but these are much less common), and are often referred to as small-cap or large-cap (cap as in capsule -nothing to do with market capitalization).
To make another sweeping generalization, we might say that large-cap mics are for the studio and small-cap mics are for the stage, but this is almost too sweeping, especially since most engineers would use a small-cap condenser as a first choice on acoustic guitar. You’ll often hear that small-cap mics are more ‘focused’, but again this is one of those words can mean almost anything. I’ve had great success using large-cap mics on guitar, though most of my favorites are small-caps.
Polar Patterns, or pickup patterns, are often overlooked but often important. A monitor engineer who worked on big tours once said to me ‘you’ll never know where to place your monitors if you don’t know your polar patterns’ and suddenly I understood the importance of it all, especially for live situations.
The seven basic patterns are: Omnidirectinal; subcardioid; cardioid; supercardioid; hypercardioid; bi-directional (also known as figure-8); and shotgun.
Small-cap mics will come in some variety of cardioid, (though I don’t think I’ve ever seen one in subcardioid), and large-cap can be any of the seven types. Many large diaphragm mics will be multi-pattern, which means you can switch between various polar patterns.
The reason this is so important for monitor placement is that each polar pattern has what are called null points, which is where the capsule does not pick up sound, so if you place your monitor right behind a null point you can have a lot more volume before feedback, which is obviously important. The Beyer M201 I use for live stuff has a hypercardioid pattern, so I place my monitor at my 9 O’clock facing the side of the microphone, whereas if the microphone were a cardioid I would place it directly behind the microphone for greater rejection (which is what you typically see in live situations).
For a big sound in a good sounding room you might want to use an omni pattern, though if you didn’t want other sounds in the room (musical or not) to bleed into the mic you might not want that. The cardioid patterns have varying degrees of directionality, with the shotgun being an exaggerated version that doesn’t usually sound so great up close.
In the studio the reason for using the various patterns have more to do with the sound you’re trying to get, and this is usually a matter of taste. Here is an MP3 of the same mic (a Neumann U89) in the same position and the same guitar, but with various polar patterns, so you can hear the differences.
The vast majority of mics have cardioid patterns, which is why you see the monitors placed facing the musician in most live situations.
Roll-Off Switches, Pads, and Frequency Response Graphs:
Some mics will have a roll-off switch (also known as a low-cut or a high-pass, since depending on how you look at it you’re either cutting off the low frequencies or allowing the high ones to pass). Typically this is a switch that will attenuate all frequencies below a certain point (typically around 80HZ). These can be very useful if things get too boomy in a live situation or if you’re just getting too much low end I the studio. Some mics will have more than one roll-off setting, like the SM81 (see below).
Another feature some mics have is called a pad. This is a switch that will attenuate the overall output of the mic by a certain amount (typically 10db). This can be really useful if your signal is so loud that even at a low gain setting on the preamp your signal is going into the red (distorting). A pad can be a life save on drums or any other particularly loud signal.
Some mics will come with a frequency response graph, and this will really tell you more about a mic’s character than you think. The graph shows you what frequencies are accentuated or which are attenuated, and ins ome cases will show you the difference between the response with or without a roll-off. So you’ll hear about mics with a ‘mid-range bump’ or ‘hyped high-end’, and this just means that all other things being equal, the mic will essentially eq your signal a little bit, and the frequency response graph shows you where that occurs.
If you know your mics’ frequency responses you can choose the right mic for, say, a muddy sounding guitar – one that will bring out the high end a little more than others in this case. Of course you can just get to know your mics and never look at one of these graphs, but they do help a little and it’s pretty easy to learn how to read one.
Here is the frequency response graph of a Shure SM81 that shows response without the roll-off and with each of the two roll-off settings engaged.
SO – that’s a lot of info about microphones. There are so many great mics out there that it would be impossible to discuss them all, but here are some of the mics I’ve used and love on guitar. These are all classic mics that I happen to use all the time and therefore know really well, so I feel confident speaking about them. I’m certainly not trying to cover every mic in the world.
Shure SM57 – Dynamic, cardioid small-capsule mic. Less than $100 and you really can’t go wrong.
Shure SM81 – a classic mic for guitars. Small-cap condenser with a 10db pad and two roll-off settings. Around $350 street and it’s a great mic.
AKG 451b – Another classic small-cap condenser. The new models have a couple of pad and roll-off settings and go for about $580, but the older ones (which don’t have pad or roll-off) are also amazing and you can get them used in the $200-300 range. This mic has a serious high-end bump around 5khz, and that’s one of the things that makes it sound great (for some reason most other mics with responses like this don’t work), but it also makes for a tricky mic on stage in my experience.
Neumann KM184 – Another classic small-cap cardioid condenser, without any pads or roll-off options. About $850. Almost anyone will tell you that the original KM84 (no longer in production) was a better mic (and costs about the same, used), but the 184 is also great. It has a similar frequency response to the AKG 451, but with less of a bump and it seems to have more ‘air’ than the 451. The main complaint about the 184 vs. the 84 is that people hear the 184 as harsher, although that’s only in comparison to the older model.
AKG 414 – Large-cap multi-pattern condenser with pads, and roll-off options. One of the all time classic large-cap condensers. Great workhorse mic that will make just about anything sound good. Around $1,000.
Neumann U89 – Large-cap multi-pattern condenser with pads, and roll-off options. Around $3200. To my ears this is the best mic out there for making stuff sound like what you’re hearing in the room. Not as famous as the U87, which most people would probably argue is the one mic to have, but I think it’s a way more versatile mic and I use mine all the time on every imaginable source. If I could only have one mic I would choose this one.
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