Live Sound University Article Wed, October 15, 2008

In the midst of talking about mics and mic preamps, the timely subject of mic modeling hardware and software has been raised. So, here’s my take on mic modelers. They may change the sound of the audio that passes through them, but there are major problems that mic modelers can’t get around: namely, the laws of physics and the limits of metallurgy. I’m not alone with these thoughts. Read on to see what Norbert Sobol, chief mic designer at AKG has to say on the subject.

Available as a preset?

I have sat semi-transfixed and listened to people who know more than you and I will ever know about microphones. As I stand on the shoulders of these giants, I can point to convincing reasons why mic modelers cannot be used to get a Neumann U 87 sound out of a Shure SM 58.

DE BASICS

First, although dynamic and ribbon mics both share somewhat similar operating principles, they operate very differently than condenser microphones. The dynamic has a coil of wire attached to a diaphragm hovering in a magnetic field. The ribbon mic has a very thin metallic ribbon quavering in the throat of a magnetic field. The basic principle is that, as long as the diaphragm or ribbon are kept in motion, a voltage is generated. If they stop moving at any time, no voltage is generated. Of course the mechanical response of a diaphragm/coil is obviously not the same as that of a ribbon, which explains why they don’t sound the same.

The physics distinguishing the condenser mic are even more marked than those separating dynamics and ribbon mics. In a condenser you have a collection of moveable and fixed electrical plates; one fixed plate, and at least one moving diaphragm, sometimes two.

The diaphragms of a condenser microphone move much more quickly in response to sound waves than dynamic diaphragms. That gives condenser microphones the ability to capture the those most subtle and fragile parts of a sound wave we call transients; very brief moments of sound that define the high frequency content of a sound.

SM57 + DSP = U47? Doesn’t add up.

The condenser capsule is also different in that a voltage is generated as long as it’s responding to a sound wave. Even if that sound could be such that it held the diaphragm micro-momentarily still in a compression or rarefaction, a voltage would be generated. That’s because a condenser generates its signal as a result of the diaphragm moving closer to and farther away from the backplate.

Even amid condenser mics, the diaphragm material makes a difference, as does the tension used to stretch the diaphragm as it’s attached to the capsule. The more tension, the less movement and the higher the resonant frequency of the diaphragm.

Older PVC diaphragms get brittle with age and that changes the character of the mic. We haven’t seen that sort of change with Mylar, but who knows how Mylar will age over time.

NICKEL OWED DION

Then there are the metallic coatings to consider. I know people who could fill your ears to overflowing about the special properties of nickel and how much a part of the early Neumann sound comes from audio engineers who know how to use nickel. For better or worse, there aren’t many nickelsmiths still alive. Now we have gold and titanium-coated diaphragms. The metal makes a difference.

Physics are also involved in what happens to the sound after it passes through the headgrille. Inside a condenser headgrille there exists a unique acoustical micro-environment comprised of the capsule, the mount that holds the capsule and the reflective and absorptive characteristics of the inside of the headgrille—along with anything else reflective or absorptive. The shape and substance of capsule’s mount base also have direct bearing on what happens to the sound before and after it hits the diaphragm. The inside grille work is also an active participant, because sound that passes through the grille to the capsule may pass the capsule and can reflect back off the inside of the grille and back onto the capsule or somewhere else.

OK, so you’re thinking, “Fine, dynamic mics can’t be used to model condenser mics, but how ‘bout one of those $200 condenser mics? Surely they can be modeled into a U 87.” Well they have a better chance, but remember there are miles of differences even among large diaphragm cardioid condensers. Distortion, frequency response, self-noise, and even that voodoo thing Neumann does with the low-end response on the U 87. You’d have a much better chance of starting with an M149 or C12 and modeling down to an SM57, but then what would be the point?

What I’m getting at is that, as effects boxes go, modelers are great for changing the way an existing mic sounds. No doubt, they will give you more sounds to play with, if that’s what you need. The ability to use digital signal processing to synthesize harmonic content and add it to the original signal allows us to do things we never dreamed of just several years ago. In fact, popular music production must have new sounds or everyone gets bored and starts pushing the walls of other envelopes to relieve their boredom.

Marketing these circuits as mic modelers and positioning them as being able to replicate the performance of a condenser microphone while using a dynamic from which to model makes compelling “something for nothing” ad copy, and, in fact, you can get close within certain limitations. I’ve EQed a dynamic mic to sound virtually indistinguishable from a large diameter condenser mic for voiceovers. In that one limited application I got really close, but with a different voice, instrument, preamp, etc. the comparison falls apart. Don’t believe me? If mic modelers were “all that”, studios would be emptying their mic closets to make room for more mic modelers. That’s the truth winking at you.

AKG’s Norbert Sobol

Norbert Sobol is the product manager and chief microphone engineer at AKG in Austria. He first joined the company in 1963, and since then allmajor developments of professional gear from AKG went to different degrees through his hands, including the C 414EB (and all subsequently improved models since then), the AKG Tube and the C 12VR, the ULS and Blue Line Range, the C 34, C 422 and C426 stereo mic’s, the C 535EB and - most recently - the SolidTube, the C 4000B, C 3000B, and the C 2000B. His long engineering history with the company makes him particularly qualified to analyze the factors involved, so I’ve asked him to address the issue. Here’s what he had to say.

Well Ty, what you explained in these paragraphs really wraps up the subject very well. As much as I had the chance to listen in to these machines (toys?), I had a similar experience to yours. Just to EQ one mic to another’s frequency response is only a minor part of the story. In the real world, time-related portions of the transmitted signal plus deviations from the ideal world due to the physical size of the microphones to be simulated will effect quite considerably the polar response over the frequency range, which in turn will effect the overall sound impression when recordings are done in a real room and not an anechoic chamber.

Then we have the effect of more or less ideal transformers used in condenser microphones together with the directly related electronic section creating a certain amount of distortion at low frequencies and interacting more or less with the microphone line and the connected equipment. These are all factors. Each one on its own will probably be not noticeable, but the combination of all of them are certainly audible.

Now once more: It will greatly depend on the overall quality level of the recording, the recorded material, the recording room, etc. etc. if such a simulated microphone stands out like a sore thumb or will go by unnoticed or even favorably in a particular recording session.

So in my opinion, these machines (hardware or software-related) should be taken as an extra and sometimes interesting aspect of experimenting with sound in a creative way and the users should not take the brand names and model numbers promised to be simulated too seriously. At the end of the day, if one achieves a sound he/she is happy with, it does not really matter what equipment it came from. Just don’t expect too much and don’t expect consistency in the sound result, which is of course you can expect if you use a decent microphone to start off with.

By the way, this last statement does not stem from my association with a microphone company but reflects strictly my personal experience in this field.

Technique, Inc. Copyright 2001
Ty Ford can be contacted directly at http://www.jagunet.com/~tford