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Wednesday, October 18, 2017

Q. What are the characteristics of vintage mics?

By Hugh Robjohns

I've been browsing a vintage microphone site and it got me thinking: what kind of characteristics are actually offered by vintage mics? Can the same sound be achieved with modern mics and EQ? Isn't most of the 'vintage sound' due to tape and valves rather than mics?
The sought-after sound of the classic vintage mics is partly down to the fact that microphones used in professional studios many years ago would have been of particularly high quality to start with — and quality tends to age well. 
The sought-after sound of the classic vintage mics is partly down to the fact that microphones used in professional studios many years ago would have been of particularly high quality to start with — and quality tends to age well.

Via SOS web site

SOS Technical Editor Hugh Robjohns replies: A good vintage capacitor mic sounds much the same as a good modern equivalent, and the same goes for ribbons and moving coils. Having said that, there has been a tendency over the last decade or two to make modern mics sound brighter, partly because the technology has improved to allow that, and partly because of aural fashion.

Also, professional mics that are now considered vintage were usually pretty expensive in their day — studios and broadcasters bought very high‑quality products — and that high‑end quality generally persists despite the age of the microphones.

Most of the vintage mics you'll find on those kinds of sites, though, are either valve capacitor mics or ribbons, and they both have inherent characteristics of their own that a lot of people revere. Ribbons have a delightfully smooth and natural top end, while high‑quality valve capacitor mics often have mid‑range clarity and low‑end warmth. These qualities can still be found in some modern equivalents if you choose carefully.

Some of the vintage character is certainly attributable to recording on tape, replaying from vinyl, and the use of valves and transformers. But some is also down to the construction of the microphone capsules and the materials used, not all of which are still available in commercial products today.

Published January 2011

Monday, October 16, 2017

Q. If speakers have to be 'anchored', why don't mics?

By Hugh Robjohns & Mike Senior

As I understand it, loudspeakers create sound and momentum, which needs to be absorbed in order for the sound quality to be accurate, so we ensure they are braced or fixed to their stands and not wobbling about too much. So surely a mic diaphragm, which is moved by incoming sound, will less accurately represent the sound if the mic casing is not sufficiently anchored. Given that we hang these things from cables, or put them in elastic shockmounts, can you explain to me why this principle doesn't apply?
Is it just to do with acceptable tolerances or is it a trade‑off between picking up vibrations from the stand and capturing the intended sound?

Paul Hammond, via email

SOS Technical Editor Hugh Robjohns replies: In a perfect world, both the loudspeaker and the microphone would be held rigidly in space to deliver optimal performance. However, we don't live in a perfect world. Sometimes a shelf is the most appropriate position for a speaker, but the inevitable down side, then, is that the vibrations inherently generated by the speaker's drive units wobbling back and forth will set up sympathetic resonances and rattles in the shelf, adding unwanted acoustic contributions to the direct sound from the speaker, and thus messing up the sound.
We 'decouple' speakers with foam to prevent annoying low‑end frequencies leaving the speakers from reaching the surface they sit on. In the case of mics, we want to stop problem frequencies from reaching them, so we support them in shockmounts.

The obvious solution is, therefore, to 'decouple' the speaker from the shelf with some kind of damped mass‑spring arrangement optimised to prevent the most troubling and annoying frequencies (generally the bottom end) from reaching the shelf. This is often achieved, in practice, using a foam pad or similar.

With microphones, we are trying to control energy going the other way. We want to stop mechanical vibrations from reaching the mic, whereas we were trying to stop mechanical vibrations leaving the speaker.

Again, in a perfect world the mic would be held rigidly in space, using some kind of tripod, much like the ones photographers use for their cameras. However, in practice, we tend to place mics at the ends of long, undamped boom arms on relatively floppy mic stands which are, themselves, placed on objects that pick up mechanical vibrations (foot tapping, perhaps) and then pass them along the metalwork straight to the mic.

The obvious result is that the mic body moves in space, and in so doing forces the diaphragm back and forth through the air. This results in a varying air pressure impinging on the diaphragm that the mic can't differentiate from the wanted sound waves coming through the air, and so the mic indirectly captures the 'sound' of its physical movement as well as the wanted music.

The solution is to support the mic in a well‑designed shockmount so that the troublesome (low end, again) vibrations that travel up through the mic stand are trapped by another damped mass‑spring arrangement and thus are prevented from reaching the mic. If the shockmount works well, the mic stays still while the stand wobbles about around it, much like the interior of a car moving smoothly while the wheels below are crashing in and out of potholes!

The only potential problem with the microphone shockmount is that it can easily be bypassed by the microphone cable. If the cable is relatively stiff and is wrapped around the mic stand, the vibrations can travel along the mic cable and reach the mic that way, neatly circumventing the shockmount. The solution is to use a very lightweight cable from the mic to the stand, properly secured at the stand to trap unwanted vibrations.

Published February 2011

Friday, October 13, 2017

Q. Where should I put my overhead mics?

By Hugh Robjohns
When recording drums, I really want to get the kick, snare and hi‑hat in the middle of the image, but with a wide spread of cymbals. The snare is placed off to the left of the kick (from the drummer's point of view). I know I need to set my drum overhead mics so that there are no phasing issues with the kick and snare mics, but how do I know where to point the OH mics? For example, if I have two cardioid-pattern mics, should they be pointing straight down, at the snare, or somewhere between the kick and snare — or somewhere else entirely?

Adrian Cairns via email

SOS Technical Editor Hugh Robjohns replies: This is an interesting one because what you are trying to do is distort the stereo imaging of the recording, compared with the reality of the kit setup. And the only way you can do that is by maximising the separation of what each mic hears. That's easy enough with the kick, snare and hi‑hat mics because of their proximity to the sources and the effectiveness of bracketing EQ. The overheads, however, remain more of an issue, because they are naturally going to pick up significant spill from the snare and hi‑hat (you can use bracketing EQ to minimise the kick drum spill, of course).

To achieve your desire of keeping the snare and hi‑hat central in the image you will have to ensure that the overhead mics are equally spaced from those two sources, so that the level and time of arrival of snare and hi‑hat sounds are equal in both mics. With that as a primary requirement, you can then experiment with moving the mics (and/or cymbals) around to achieve the required spread of cymbal sound. Angling the mics, to assist with the rejection of as much snare and hat spill as possible while capturing the wanted cymbals, is also a useful tool, providing you maintain the equal distance so that whatever spill is captured remains central in the stereo image.
To get a particular section of your drum kit central in the stereo image, it is important to set up your overhead mics such that they are equidistant from the relevant sources. 
To get a particular section of your drum kit central in the stereo image, it is important to set up your overhead mics such that they are equidistant from the relevant sources.

There are also some less conventional alternative techniques you might also like to consider, using fig‑8 mics where you can aim the deep null to minimise snare and hat pickup in a useful way.

Published March 2011