Tuesday, August 28, 2018
Top tips : Microphones
What's with mics?
Microphones are one of the main items in any radio studio. The microphone was invented before transmitters, receivers or recorders... what were they thinking??
Even if you have nothing else in the studio but a microphone, you can communicate to your listeners and generate compelling programs. And of course there are some things you should know to ensure you get the best out of the microphones in your studio.
So here we go with John's Twelve Top Tips and Terms of Mics.
All microphones have a pattern - that's the technical term that tells you in which directions the microphone will pick up sound. An Omnidirectional microphone picks up sound from all round. It doesn't matter if the microphone is pointing towards you or away from you, it will pick up the sound equally well. Directional microphones include "cardioid", a sort of flat heart shape; hypercardioid, which is much more directional; figure-of-eight, which picks up sound from the front and back but not from the sides. Most directional microphones are cardioid, and that's the most popular pattern in a studio.
Tip: omnidirectional microphones make better sense for handheld interview work. You might think that a directional mic would pick up less unwanted noise. True. But in an interview, you will move the mic between you and the subject, and an omnidirectional mic will still pick up a lot of the both of you, no matter who the mic is pointing towards.
Tip: an omnidirectional mic will not sound muffled because you point it away from you. But it will sound more distant if you move it further away.
Microphone types include Condensor, Dynamic, Ribbon. There are a couple of others, but you won't see them in professional situations. Dynamic microphones are the most common, and produce a signal directly from the sound that hits the mic. Ribbon microphones have a metal ribbon inside a magnetic field. You probably remember seeing the big radio microphones of the radio serial days; they were ribbon microphones and had a figure-of-eight pattern.
In a condensor mic, the air vibrates a very light plate and the electrical change is measured. There is so little signal produced that an amp is needed at the microphone head, and that's why condensor mics need power.
3. Microphone power
Power can be supplied to a condensor microphone via a battery in the mic, but that's not convenient in a studio. These days most condensor mics are "phantom powered" which means that the power is provided by the mixer down the same wires used for signal. Sounds hairy but it works very well.
4. Electret is not bad
An "electret" is another way of describing a condensor microphone in which the diaphragm is permanently polarised. Early electret microphones were not wonderful, and the term "electret" got a bad reputation.
Many manufacturers just use the term "permanently polarised" to avoid saying "electret". What you call it isn't important: today's electret microphones are very very good. If you like the sound of a microphone, that's worth much more than its technical description.
Some microphones need to be indestructible - just look at what happens during a live music gig. Studio microphones don't get the same amount of bashing, but they are often mistreated.
A big difference between cheap and expensive microphones is how well they handle being dropped. More money gets you better construction and (hopefully) longer life.
6. Proximity effect and bass rolloff
All directional microphones have "proximity effect". As you get closer to the microphone bass frequencies are emphasised. And not just voice - anything closer to the mic will have the bass emphasised. Sometimes that sounds nice, and sometimes it makes the sound muddy.
Many studio microphones have a bass rolloff switch to compensate, and some like Sennheiser's MD-421 even have variable rolloff. Many microphones are designed so that you can't get too close to the diaphragm, and that limits the proximity effect a bit. In a radio studio it's very important to understand how the mic sounds when you get closer and further away, because you can't control how guests move during an interview.
7. Pop shield
Plosives produce palpable pantheons of powerful perturbation. Translated: words with the letter P generate large amounts of very fast air - enough to overload the microphone. Pop shields break up the air and stop the microphone from over loading. A good pop shield is essential for a studio. Plus you can always take the pop shield off and wash it... although if it's dirty enough to wash, it's probably time for a new one.
Hint: use water and maybe just a little dishwasher detergent, and RINSE the pop shield a lot. Then dry it in the sun. Don't put it in a drier or an oven... it will be game over and very messy.
8. Check mics for phasing
A bit esoteric, but very important. All mics used in a radio studio must have the same phase relationship. You can check this easily. Put the mics side by side, as close as possible. Talk into them both.
Set the mic channels separately so that the two mics produce the same meter reading. Now turn them on together.
If the sound gets louder or fatter: the mics are in phase. That's good.
If the sound gets thinner: the mics are out of phase. That's bad.
9 Preserve absolute phase
Even more esoteric but REALLY important. Your studio must preserve absolute phase between the microphone and your headphones. Your brain knows what your voice sounds like. If your studio electronics inverts the sound before it gets to your ears, it will sound weird. Not everybody can tell you what's happened, but most presenters will know that it doesn't sound right.
10. Use similar mics in a studio
If you have a presenter and a guest talking in a studio, some of the presenter's voice will always get into the guest mic... and vice versa. Think about it: if the two microphones are different, then the leaked sound will be different, so your guest and presenter will sound different.
How different? Maybe a lot, maybe a little. Now add a few more open mics, and think about what happens. Make life easy on yourself, and use all the same mics.
11. Set all mics to have same gain at same fader position
Much easier to do if all the mics are identical. When you turn up the microphone on a quiet guest your listeners will hear a nice warm sounding guest, and a more hollow sounding presenter.
Why? Because more of the presenters voice is now leaking into the guest mic as well as the presenters mic, but the guest mic is further away. Your best defence against mics that sound unbalanced is to carefully sent them all up to be identical, and then get everyone talking at the same loudness. By the way: that's what people do in conversation, so it's not so hard.
Listen to microphones. That's the best way to compare them. But don't use your own voice: put microphones in front of other people and listen in a control room. That's the only way you will be able to hear the subtle differences.