[Wylug-discuss] Seeking Advice: Quality Mobile Sound Recording Q: Interview Microphones

[Roger Beaumont]

Long post...

Dave Fisher wrote:
> On Wed, Nov 29, 2006 at 04:17:11PM +0000, Phil Driscoll wrote:
> 
>>This type of dynamic mic (RVD30, SM58 and similar) is best suited to close up 
>>work placed right next to a mouth or a musical instrument. As with all 
>>cardioid microphones, the closer they are positioned to the sound source, 
>>the 'bassier' they will sound - and as they are designed for close up work, 
>>their frequency response is tailored to compensate. Hence, in an interview 
>>type situation where the mic may need to be a foot or more away from the 
>>speaker, they will tend to sound too 'thin'. However in an environment where 
>>there's a lot of background noise or a PA, then a mic which works close up is 
>>an advantage.
> 
> 
> Thanks Phil, and everyone else who has contributed to this thread.
> 
> Like so many great contributions to the thread, Phil's points have
> raised far more questions in my head than I could post in a single
> message (or possibly even in a single thread).
> 
> I think it might be wise to keep things simple by posting one question
> at a time.
> 
> If people feel that this is all too far off-topic for wylug-discuss, let
> me know and I'll try to take the discussion elsewhere.
> 
> Anyway, my first question is:
> 
>   If dynamic or cardioid microphones are really only useful for close-up
>   interview usage (i.e. where you want to more-or-less eliminate ambient
>   noise), and condensor or a back-electret microphones are better suited
>   for acoustic intruments, what would you recommend for:
> 
>   a) A quieter interview situation
> 
>   b) A noisy environment in which you can't stick a microphone directly
>   under someone's nose?

You seem to me to be confusing three issues there, Dave.

One is the technology: electret condenser versus 'dynamic' (more 
technically, 'moving coil'); the second is the polar response - cardioid, 
hyper-cardioid (aka 'shotgun'), or omni-directional; the last criterion is 
proximity design.

In reverse order:

Sound basically obeys an inverse square law: n times as far away, it is n 
times n weaker, however, that is somewhat modified by diffraction effects, 
so that low, bass tones seem to fall off more rapidly because they are less 
directional.  Mic manufacturers take all that into account, so that those 
made for close use (e.g. a rock singer on stage, or interview in a noisy 
environment, where the voice is close to overpower all the other noise) so 
they are deliberately designed to under play the bass, which will be 
relatively louder in close-up voices.  (Simply get someone to talk to you 
from a 'normal' distance, then do the same within a few centimetres of your 
ear - you'll hear just what I mean.)  Others are designed for use at a 
distance and their diaphragms have a looser suspension so they give the 
bass full emphasis.

This is probably the most important issue for your work: will you be using 
the mic right under your people's noses, or from a distance?

Next is the 'polar response'.  Fundamentally, sound is just pressure in the 
air, which cares absolutely zilch about where it came from.  However, by 
designing the housing of the mic right - different lengths and slots in the 
side of the housing and so on - a mic can be made to be more sensitive to 
sound from the direction in which it 'points'.  The extreme is called a 
'gun mic' and is very much more sensitive in the direction it points as in 
other directions (at right angles, or behind).  Omni-directional mics only 
care about distance, 'cardioid' mics care about direction too, 
hyper-cardioid mics care more even more about direction than distance, but 
distance still follows that inverse square law.

This is criterion number two for you: how much do you want it to matter 
where you are pointing the mic?

The last point is technology.  Condenser mics need power: batteries or 
'phantom power' (which just means it's sent up the wire by the mixer, or 
whatever).  In contrast, dynamic (moving coil) mics don't need that: the 
diaphragms in those simply move a coil of wire through a magnetic field and 
thus, just like any dynamo, they produce electricity.

There are lots of practical issues about which is best under any given set 
of circumstances, but they are so model dependent that I can't give any 
useful, general advice beyond that dirt-cheap unpowered mics are usually 
crap, while the cheapest condenser mics can be OK.

It probably won't help you make a decision, but an important factor is what 
the venue (I'm talking about music here) will tolerate and the size of the 
venues.  Will they let you set up mic stands and such where _you_ want, or 
will they insist that you be inconspicuous?  A (couple of, assuming you 
want stereo - yet another issue) gun mics at the back of the room might 
well be a good decision (if you get them on tall stands, so they are not 
close to the audience).  Add a 'proximity' mic for interviews, so that you 
_can_ stick it under their chins to make their voices louder than other 
ambient noise (one on one, stereo is a post-production issue) and you 
should be OK to have a go and start to make up your own mind.

Oh yeah, the final issue is 'balanced' versus 'unbalanced' - which shows up 
in practical terms as 'jack plugs' versus 'XLR' (though some equipment uses 
a 'stereo jack' to implement mono, balanced line).  This matters if you 
have long leads - more than a couple of metres or so.  'Balanced line' kit 
uses 3 conductors: an earth plus negative an positive signal wires. 
Everywhere there is unwanted magnetic interference from fluorescent lights, 
fridge motors and who knows what else.  If the mic lead is short, that 
isn't significant, so unbalance wires are OK.  If on the other hand your 
leads run all round a room (especially if it's a big room) then the 
so-called screening, picks up that interference.  With balanced line kit, 
first of all the earthed screening cuts it down, then both positive and 
negative signal wires pick up what's left in equal measure, so the 
difference - the signal you are recording - is zilch (if only life were 
that perfect).  The bottom line is that balanced line systems are Much more 
interference resistant than unbalanced.  For the stage recordings (long 
wires) use balanced line.  For the interviews, it doesn't matter.

Hope that helps,

Roger