Of Mics and Men - Multiple Microphone Techniques
Sound engineers are naturally obsessed with microphones. Microphones to audio nerds are like women to a playboy: he wants to go through all of them but he only has time for so many. Risqué analogies aside, we do love trying them out. (The microphones, not the women, stay with me here.)
I wanted to demonstrate the different sounds the typical microphones sound engineers use in their day to day work, with audio samples of how each microphone sounds and how much of a difference a little positioning can do to your sound. Pure Wave Audio was gracious enough to lend me a few microphones, one of them being the ultra-awesome SE Electronics VR2 ribbon microphone. With each type of microphone in hand, I set out to explore some of the standards in microphone techniques, using a typical instrument everybody will record at some point, the electric guitar.
In the following examples I'm using three different microphones: the dynamic, the condenser and the ribbon. I am using the Audix CX-112 large diaphragm condenser, the Audix i5 dynamic and the SE Electronics active ribbon microphone.
Dynamic Microphones – Dynamics are sturdy and tough. Compared to the condenser mic dynamics have a narrower frequency range. They are great for instruments that are loud, since they don't distort easily and can take a beating. Easily found in live sound, on drum kits and in-front of guitar cabinets.
Condenser Microphones – Condenser sound full and most accurately capture the actual sound of the instrument. They are used for any situation, most notably on vocals, full range acoustic instruments and overheads on drums.
Ribbon Microphones – Usually considered fragile and expensive, but with new technology they are quite a bit more sturdier than they were in the old days. They usually have a fairly balanced frequency response but do tend to have a slight roll-off in the higher frequencies, resulting in that silky smooth sound you have heard on old recordings.
Recording in a Home Studio
Be aware when recording in a home studio to take all the environmental issues into account. I put baffles and blankets all around where I think the walls or objects are going to interfere with my sound. I have a movable baffle that I move around to absorb outside sound or minimize reflections. Make sure that you take some precautions if you live in a noisy area so you don't need to re-record due to extraneous noise halfway through your take.
Microphone Techniques and Audio Examples
In these examples I will be demonstrating a few mic techniques and positions using the electric guitar amp. It's a convenient way to demonstrate the difference in microphones and sound, especially since most engineers will face the electric guitar amp sometime during their careers. Some of the theory doesn't only apply to the electric guitar amp and can be used for any other recording purpose. The aim is to give you and understanding of how the different microphones sound and how they can work together, whatever instrument you choose to record.
When recording the guitar amp many engineers stick a dynamic microphone in front of the cone and be done with it. This is certainly a valid method and has produced some great guitar sounds over the years, but there is a difference in sticking a mic in front of the cone and actually finding which part of the cone you should, well, stick it in front of.
By just playing the same guitar part, a clean chord progression with three different positions of the microphone in front of the cab I am able to produce three completely different sounds by just moving the microphone around the cone area.
Directly in front of the cone
Sticking a dynamic in in the middle gives you an edgy sound, not bad at all, but it tends to have more bite to it than you might like.
At the edge of the cone
If you move the microphone all the way to the edge of the cone you get a muddier sound that's not so well defined in the highs and has a fair amount of low mid character to it.
At the sweet spot
There's always a sweet spot right? There is always that one point on an instrument or amplifier that gives you the exact balance you want. In this case our sweet spot is in the middle of the cone, by the edge of the dust cap. This position gives me a balanced sound of highs and lows without too much muddiness or attack.
Let's do a quick comparison to how a dynamic and condenser sound like at the sweet spot. This is the exact same performance miked up with both microphones at the sweet spots around the cone. Notice the incredible difference in sound from one microphone type to the other.
The Dynamic at the sweet spot
Gritty and bassy sound with a fairly balanced frequency response. A cool sound, especially for this type of playing.
The Condenser at the sweet spot
A little wiry sound. It's kind of like the high end response from the condenser accents the wiry single coil sound from the guitar.
Now, when we put both of them together we have a different type of sound. A wiry single coil rock funk sound with enough bassiness from the dynamic to make it tough and punchy.
You can move the microphones so that they are facing the cabinet at different angles. Straight on isn't the only way and combining different angles and positions results in different tones. Listen to this audio sample of a condenser facing straight on the middle of the cone while the dynamic is positioned at a 45° angle towards the cone as well. A subtle change but a well heard difference in sound.
Say we are not satisfied with the bass response of the microphones and want more meat to our sound. We know that the dynamic at the edge of the cone had a pretty muddy but bassy sound that we might be able to use in conjunction with our condenser sound to get what we want. With different angles and different microphones picking up the various characteristics of the sound doing close miking on the cabinet might be all you need to get a great sound. Additionally, these audio samples have both channels playing at the same volume so by playing with the levels of the microphones you can get the correct balance you want.
Ribbon and Condenser
Let's take a break from the dynamic for a little bit and hear how these two microphones interact. You've been listening to how the sweet spot can give you a fairly balanced sound and by combining the gritty dynamic and the clean condenser you get a nice balance of the two types. Now let's throw the ribbon into the mix instead of the dynamic and see how the sound changes.
Ribbon and Condenser on the sweet spot
We're not inventing the wheel here, we're just experimenting and analyzing how the sound changes so take a listen to the same riff, with the two microphones in the same sweet spot position.
Notice how there is less bite with the ribbon in the mix instead of the dynamic. The dynamic/condenser combo sounds more modern rock while the ribbon/condenser has an older and smoother sound.
Remember the first statement of how sound engineers are used to sticking a dynamic in front of the cone a calling it a day? Well, sometimes experimentation and different microphone selections pay off.
Listen back to the audio sample of the dynamic in front of the cone, the one we started off with and a position some people pick by default:
And then listen to the two different microphones in the sweet spot:
Whichever you choose(I prefer the second one) make sure that you aren't just selecting a microphone position because you are lazy. Choose it because it sounds good.
Multi Microphone Techniques and Room Mics
Depending on your zeal and number of microphones you have at your disposal you might get even more experimental with your techniques, trying out every possible distance and combination of mics. In the following examples I'll try to demonstrate the difference between close miking, distance miking and ambient miking all on the same signal. By comparing the audio samples and mixing them together you will be able to understand how to grab that signal you hear in your head the next time you find yourself with a microphone in hand and a musician in room.
First of all: Phase
There is no territory more dangerous and prone to phase problems than multi-distance miking techniques. Due to the way sound waves behave you might have two microphones listening to the signal at different times resulting in phase cancellations of frequencies and overall bad news.
Just to demonstrate, here is an audio example of a rock guitar riff that was recorded with three microphones. The first one was with the condenser at the sweet spot, the dynamic at a 45° angle and the ribbon mic picking up the ambience in the hallway outside the studio. If you don't take care to make sure you have all the signals in phase you can end up with a signal that's devoid of low end and fuzzy, like it's coming from a speaker you got from a cereal box.
Recording with waveforms in phase:
Recording that's out of phase:
Listen to how drastically the sound changes just because the microphones are out of phase. All the low end is missing and the sound seems filtered and weak. There is no reason to have that happen if you just make sure all your waveforms are in phase. How? Easy. Just zoom in and see if the crests and troughs are lined up with each other. Because if they aren't, that's a sign of an out of phase signal. If you invert either signal so that they align you should hear all the body and punch coming back into your recording. So if you recorded it badly to begin with you shouldn't worry too much because you can always fix it in the box, even though it's always better to get it at the source.
Now, each microphone position gives you a different sound, and there is no better way to demonstrate than to let you listen to how each position and microphone sounds. I didn't record each and every microphone at every position but I did want to give you a sample of the different distances and how they sound.
Dynamic at sweet spot
We're doing a simple clean chord progression and the dynamic at the sweet spot isn't anything you haven't heard before:
Condenser at around 2 feet
I've decided to move the condenser microphone a little bit out to capture the fullness of the amplifier. It's all good to listen to a specific spot at the cone but like Alan Parson's says, sometimes you want to hear how the amp actually sounds.
Listen to the tiny added ambience without giving it a “roomy” sound.
Ribbon in the hallway
I've placed the ribbon microphone in the hallway outside my studio to capture the ambience from the amplifier. It's not that far away, or around 12-15 ft or so, but it still gives you a noticeable ambient sound. Far away, but still fairly close.
Since we have such a great bunch of sounds that captures our playing how about we put it together and listen back to how it sounds?
Oh, don't you just love it when it all comes together?
I hope you've gleaned some knowledge and information from the above material. Microphone positions and techniques is an art, everybody kind of follows the same rules but nobody is looking for the same sound.
Most people want the same thing: a balanced sound that has character and fullness. Being aware of the difference in microphones, the multitude of positions you can use as well as taking care of potential phase problems are all things to have in mind next time you are getting ready to record.