Issue 192 - Microphones

 Editor,
 
Mr. Balfour’s letter in issue 192 and Mr. Harley’s column raise some interesting points.
 
I’m not sure how practical it would be for most audio reviewers to write pieces on microphones.  While it may be possible, I would think one gets a better picture of a piece of gear by putting it to its intended use.  With mics, this would involve making recordings of a variety of instruments in a variety of settings – things that would likely be more difficult for the typical reviewer than installing say, a new amp, turntable or CD player in their playback systems.
 
While I am in complete agreement with Mr. Harley regarding the wonder of listening to a mic feed and also in agreement that well done high resolution digital (I’ve been recording at 24/192 since last year) can indeed sound like a mic feed, it is important to note the sound of the mic feed itself is dependent on several issues.  And that a mic feed in a typical studio is not the same as a mic feed from a minimalist, purist mic array.
 
First, the microphones used in typical studio recordings (all musical genres) tend to be large diaphragm mics with cardioid pickup patterns.  For those to whom this is new terrain, a cardioid pickup pattern (so called because it is graphically represented by a shape somewhat akin to a heart – a real one, not the Valentine’s Day sort) means the microphone is “directional”.  It tends to hear mostly what is in front of it.  Sounds to the side are suppressed and sounds to the rear suppressed more.
 
In contrast, a figure-8 pickup pattern (so called because it is graphically represented by a shape that looks like a number 8) means the microphone is “bi-directional”, sensitive to sounds from both the front and the rear, while suppressing sounds from the sides.
 
An omnidirectional microphone (graphically represented by a circle with the mic in the center) hears sound from all directions equally.
 
Let’s look at those large diaphragm, directional mics for a moment.  The are directional primarily in the treble, becoming less so with decreasing frequency.  This means sounds arriving at the mic from off-axis (i.e. not from directly in front of it) will still be picked up but with a skewed frequency response.  This is one reason why I sometimes say “All mics are omnis.  Some just have colored off-axis response.”
 
The off-axis colorations are somewhat dealt with by close placement to the sound source.  This raises other issues which I’ll get to in a moment.  The large diaphragm in most commonly used mics also adds a coloration, often manifested as a resonance peak in the treble.  Those highly touted German microphones have a 6-8 dB peak at 8 kHz.  A typical cardioid will also have a roll off in the bass starting around 50 Hz and another roll off in the treble, around 15 or 16 k Hz.
 
Contrast this with a good small diaphragm omni, which can have a frequency response that looks more like a good amplifier’s; ruler flat, with the best ones extending from single digits in the bass to 40 kHz or higher.  These mics do much less editorializing of what they capture than anything else in my experience.
 
But modern studio techniques and the desire to isolate sounds from one another, so they can be re-balanced and mixed together later, have resulted in those large diaphragm cardioids being the most used for most typical recordings.  Couple this with the tendency of these mics to get an additional peak in the mid/upper bass when used very closely and you understand why many pop vocals sound “thick”.
 
Then we must consider the cables used to connect the mics to the mic preamplifiers.  Typical studio cables will measure well in terms of resistance, inductance and capacitance but in my experience, they are no sonic match for the best audiophile type cables.  Not too long ago, I tried a pair of balanced Nordost Valkyrja cables to connect my mics to the mic pres.  I was pretty shocked at how thin, grainy and opaque they made my old Mogami Neglex pro cables sound in comparison.  The Mogamis are fine cables but they’re no match for the Nordosts.
 
This brings me to the experiment conducted by Mr. Meitner, as related in Mr. Harley’s column.  As I understand it, the goal was to see if a 10” speaker in a guitar amp could accurately reproduce a sound that was originally made by that 10” speaker.
 
I find the experiment curious because there is no way I would expect the reproduction in such a test to sound anything like the original sound.  First, no microphone was involved in creating the original.  On the one hand, we have a high impedance guitar input fed directly from the guitar’s pickup(s) energizing the speaker.  And on the other hand, we have a microphone (the type of which is not described – was it a large diaphragm cardioid? a small diaphragm omni?) picking up that original sound from the speaker (the distance and orientation of the mic and amp is not described) via the air, within the acoustic space of the room –assuming this was done indoors.
 
Even with the best small diaphragm omni in an anechoic space, connected with the best mic cables to the finest mic preamps, too many things are different.  Why expect otherwise?
And why expect a speaker designed to produce sound to be equally adept at reproducing that sound?  Isn’t that a bit like expecting a clarinet reed to be able to reproduce the sound of the clarinet?
 
Just my perspective.
 
The amazing thing is that even with the colorations of the studio mics and cables, etc., the total result still sounds a whole lot better than it will after it has been recorded by an analog deck or by a typical digital one.  High res digital (4x rates like 176.4 and 192), done well really does sound like the “recorder” has been removed from the equation and one is hearing the mics directly.
 
It remains up to the engineer to select the mics and associated gear and to implement them in a way that will capture The Absolute Sound.
 
Best regards,
Barry
www.soundkeeperrecordings.com
www.barrydiamentaudio.com