Location Audio Techniques

The Mics

The main component to a quality location recording is the microphone and how it is used. Many commercial classical recordings use multiple microphones and then attempt to reconstruct the original soundscape by adjusting levels and panning (horizontal image placement) when mixing. The most commonly articulated reason for using multiple close mics for a classical performance is to provide additional detail that gets lost in the space of the room. Often, the acoustic space is separately miked and added in later. Sometimes artificial reverberation (typically convolution) is added to provide a more natural sounding acoustic if the room is deficient.

A different philosophy is the "purist" approach (a pejorative term, but one I'll perpetuate for now), which uses a minimal number of microphones to capture the performance. The placement of the microphones completely determines the ratio of direct to reverberated sound and the level of detail. Clarity is often better with a smaller number of microphones, since there are fewer acoustic interactions between mics (no smearing due to phasing and comb effects). Fewer microphones also mean that visual impact is lessened.

The Approach

I generally (but not always) subscribe to the purist approach, both for philosophic and practical reasons. It is obviously easier to not have to set up a forest of microphones and stands, but there is a down side; mic placement is extremely critical with any minimal technique. Also, the quality of the acoustic space will be dutifully recorded, so strange reverbs, acoustic echoes or traffic/airplane/HVAC/audience noise may become an annoyance that is permanently documented. However, it is my opinion that a minimalist recording setup almost always provides a superior quality recording in a good acoustic space.

Though I have made good recordings by just throwing some mics up and making some educated guesses about the acoustics, truly excellent results require careful experimentation in mic placement (and musician placement, especially in the case of a recording session). I prefer to have at least a half hour with the performers to adjust mic placement and levels. Moving performers (especially soloists) around may be what it takes to provide correct balance, but this would be done only if it does not compromise the live performance.

If I'm using an AKG C-422 remote pattern stereo mic, it is possible to adjust the direct/reverberation ratio silently while recording. However, I strongly prefer actual mic placement than twiddling knobs because the sound and spacial characteristics are noticeably better when the mic is physically in the right place.

More recently, I've been using a pair of Neumann KM 183 or Earthworks QTC-30 omnidirectional mics with a Jecklin disk as the main stereo pair. The low end and imaging with this set up is just amazing.

Often, I'll use a main configuration (AB, OCCO, CR Fine, ORTF, Decca) with spot mics to mix in a little extra presence (for, say, a little brighter harp in a large orchestra, or solos in a big band).

The Space

I am not too much of a purist to reject the application of "artificial" technology to come up with a more satisfying recording. If an acoustic space is too dead or has some noise problems, a better result may be accomplished by miking the musicians more closely and then adding some digital reverb later. The technology should always be in service to the musical result.

So, here's a short list of what's required for a superior recording space:

  • Smooth, balanced reverb time appropriate to the size of the room
  • No "slap-back" echoes due to parallel surfaces
  • Quiet ventilation system
  • Distance or isolation from traffic and other outside noises