Audio Recording Microphone Technique Basics

  

Orchestral Miking (spaced omnis - "T" stand) Orchestral Miking (Spaced Omnis - "T" Stand) Adlib Steel OrchestraMost audio recording techniques can be classified as either "orchestral recording" (also referred to as "orchestral miking"), or "close miking".  These two techniques, as used for stereo recording, are discussed below.  Monaural is similar but with fewer microphones.  Surround sound adds a fair amount of complexity beyond what is discussed here.

There are advantages and disadvantages of both miking techniques.  I use orchestral recording for most of my steelband recordings, with the occasional addition of spot microphones.  Either technique, or a mix of both, may well produce the best results in a particular circumstance.  Achieving the best result depends on the acoustics of the recording venue, the size of the group being recorded and the presence or absence of vocalists or "electronic" instruments.  Additionally, the choice of technique to use may be influenced by external considerations, such as the equipment available and the budget; the amount of time available for setup, checkout and rehearsal; the presence or lack of sound reinforcement if the recording is a live concert; and a myriad of other factors. This article is an attempt to describe the two techniques, the differences between them, and the advantages and disadvantages of both.


 

What are Orchestral Recording and Close Miking?  What are the Differences?

Orchestral recording is just what the name implies: Making a recording (particularly of an orchestra, but the technique works for smaller aggregations) with a minimum of microphones.  They are placed to capture the audio (music and room acoustics) as it would be heard, under optimum conditions, from the best seat in the house.  Microphones are usually placed at some distance from the musicians, where there is a balanced acoustic mix of the musicians and the room acoustics.  The output of the microphones is typically recorded as a stereo track which, probably after some post-production processing, becomes the stereo master.

Close miking, in its purist form, involves placing microphones close to the musical instrument so as to pick up the sound of that instrument with a minimum of sound from the environment (room acoustics, noise, etc.) and from other instruments. Except in the case of soloists, this usually involves several microphones, often one or more per instrument, and either a mixing console or a multitrack recorder.  The multitrack recording is mixed down in post-production, usually to a stereo master.  The ultimate in close miking of an electronic instrument, like a keyboard, is not to use a microphone at all, but rather to use a "direct box," which connects the electrical signal generated by the instrument directly to an input of a recorder or mixer.

There are, in fact, an infinite number of combinations and variations of these techniques. You may add "spot mics" which are close miking instruments (or vocalists) in the orchestra/band that may not be picked up well by the orchestral mics, and (usually) record them on separate tracks to be mixed down in post-production.  Or, conversely, a set of stereo "ambiance" microphones may be added to a close-miked session, in order to capture the acoustics of the space and add some of the room character to the final mix.


 

 Orchestral Recording Basics

 Under the proper conditions, an orchestral recording will most closely capture of the actual performance.  If the number of instruments is large, it is the only practical way to capture the entire orchestra.  It is the technique least prone to operational errors, and can also be the simplest and quickest to set up and take down. If the acoustics of the performance space are good, the recording will capture the "sound" of the space.  If you are making a "live" recording with an audience, but without amplification, you will capture the ambiance and applause of the audience in the recording.

There are a number of different orchestral recording techniques, many dating from the earliest experimentation with stereo in the 1930s and some of more recent origin.  All are based on the performance characteristics of the particular microphones employed (especially their directional patterns), and the laws of acoustics and physics.  All of these techniques have particular advantages and disadvantages. Some may work better than others in a particular environment and for particular applications.  Be aware that all of these techniques involve using specific microphones at particular locations, often oriented in particular directions.  They all require that the microphones be located some distance from the musicians, in order to pick up a sound field that has been acoustically mixed. To some degree this is analogous to what your ears hear in the vicinity of the microphones.  A further description of some of these techniques is on the next page.

As I will repeat several times, setting up two nondescript microphones at random locations directly in front of the musicians is not a proper orchestral recording technique and will, in all likelihood, result in a poor recording.


 

Some of the More Common Orchestral Recording Miking Techniques are:

  • Spaced Omnis: Two omnidirectional microphones located from a few inches to a few feet apart, some distance in front of the orchestra. 
  • Blumlein: (Named after Alan Blumlein, the inventor of many stereo recording techniques.)   Two bidirectional (figure-8 pickup pattern) microphones, located together (usually one above the other on a common stand) one oriented 45 degrees to the left of center, the other oriented 45 degrees to the right of center.  As with spaced omnis, they are located some distance in front of, and possibly slightly further away from the musicians. (This additional spacing also applies to the X-Y and ORTF techniques below.)
  • X-Y stereo: two directional microphones usually with a cardioid pickup pattern, placed with the microphone elements (front of the microphone) almost touching and at an angle of 90 to 135 degrees to each other.  There are brackets, called stereo microphone bars,  available which attach to a microphone stand and hold the microphones in the proper orientation for this and several of the other common orchestral techniques.
  • ORTF stereo: (Named after the French broadcasters who developed the technique.) Two cardioid microphones oriented at an angle of 110 degrees to each other, with the elements spaced 17 cm (about 7 inches) apart horizontally.  The microphone on the left should be facing to the left of center, the mic on the right should be facing to the right.  This means that with long microphones, the rears of the two microphones may well have to cross each other.  Using a stereo microphone bar with an ORTF setting will help assure correct spacing and orientation of the microphones.
  • M-S or Mid-Side stereo:  A bi-directional (figure-8) pattern microphone facing sideways to the musicians, which records the stereo difference signal between the left and right, and a directional (often cardioid) mic aimed at the musicians which records a monophonic signal of the performance.  The use of M-S recording requires a matrix to make the left and right signals.  The matrix may be a piece of hardware, or often now a software "plug-in" for an editing program.

    There are variations of the above techniques and a number of other stereo miking techniques, each of which has advantages and disadvantages.

 

Circumstances Under Which Orchestral Recording Will Present Difficulties and Quite Likely Will Fail to Give a Proper Capture

  • When the acoustics of the space are unsatisfactory.
  • When there is significant "foreign" noise present: Airplanes, traffic, nearby DJ's, noisy machinery, and other sounds that may not be anticipated.
  • When amplification is being used for sound reinforcement, unless great care is used in the selection of the orchestral recording technique, and in the speaker location and volume level of the sound reinforcement system.  It is vital to keep any "spill" from the sound reinforcement system from being captured by the orchestral microphones.  Such "spill" will almost always result in a very poor sounding recording.
  • When the orchestra cannot be positioned such that the instruments will be captured in the directional locations desired in the soundfield.
  • When there is insufficient space in front of the orchestra to allow the microphones to be placed so as to properly capture the acoustically mixed sound of the orchestra.
  • When a live audience is not controlled and crowds into the space in front of the microphones, and/or carries on private conversations that are captured by the microphones along with the music.
  • When one or more instruments are not balanced with the rest of the orchestra.  If the instruments are too loud, and cannot be played more quietly, it will be necessary to move them significantly further from the microphones.  If too soft, it will be necessary to either move the instrument(s) closer to the microphones or use additional "spot mics" to capture the instrument(s).
  • When there are solo vocalists present, you may find that you have to employ spot vocal microphones to capture their voices, particularly for pop music.

Most recordings of large orchestras or choruses are typically based on one of the orchestral recording techniques. 


 

Close Miking of a Sax (not optimum mic placement)Close Miking of a Sax (not optimum mic placement)Close Miking Basics

A multitracked close miked recording, if properly done, will give the recordist the most flexibility in editing and mixing the final recording.  With the proper equipment and trained musicians, the different instruments and vocals can be recorded at different times, and tracks can be replaced or re-recorded individually.  The recordings of individual instrument tracks will typically have more "presence", as less of the acoustics of the space is recorded in each track.  This also means that if the performance is being amplified for sound reinforcement or the acoustics of the space is undesirable, you have a much higher likelihood of capturing a good recording.  You get the ability to dynamically adjust the balance of the instruments/vocals by mixing the tracks in post production.  You may have the opportunity to share some of the same microphones for sound reinforcement and recording by using "mic splitters".  This is a technique typically used to get professional recordings or broadcasts of live pop music concerts.  Finally, you can "process" individual tracks in an infinite number of ways, applying frequency equalization, dynamics control, reverb or special effects to the individual tracks or selected groups of tracks before mixing the final recording.


 

There Are a Number of Issues in the Use of Close Miking and Multitrack Recording:

  • If the size of the orchestra is large, like a symphony or panorama steelband side, the number of microphones and recording tracks required becomes impractical.  You essentially need one or more microphones per instrument, or in some cases, small group of instruments.  Attempting to multitrack and close mic by recording only one or two of a group of the same instrument may seem to give a satisfactory recording, but you basically saying that the musicians and instruments that were not miked might as well have stayed home.  They are not part of the final recording.
  • In order for close miking to work, the microphones must be located so that they pick up the desired instrument(s) and reject the sound from all other instruments.  The choice of particular microphone models for particular instruments becomes of particular importance when close miking.  The recording engineer has to know the pickup patterns of the chosen microphones and position the microphones carefully so as to reject the sound from other nearby instruments.  Otherwise you will find that when you mix the multitrack down you will end up with "mush" and quite possibly weird sounding frequency distortions created by nearby microphones picking up the same instrument(s) at similar levels.  It is typically more important to position microphones to reject unwanted sounds than it is to position them on axis to capture the sound of the desired instrument.  The choice of particular microphones should also be made to complement the sound of the particular instrument or voice being recorded, different model microphones have very different "sounds".  This is very different from the choice made for orchestral recording, where one wants microphones with a flat frequency response that does not emphasize a particular range of the audio spectrum.
  • Proper microphone orientation becomes a serious problem, particularly if the instruments are crowded together in a small space, and/or if you are attempting to capture groups of instruments with a single microphone, as this precludes tight close miking of a given instrument.  Successful simultaneous multitrack recordings very much depend on isolation, as described above.  This isolation is much easier to obtain if the instruments are spread out in the recording venue.
  • If the acoustic sound of an instrument comes from more than one point on an instrument, such as the case of a piano, you may have to use more than one microphone and track on the instrument.  In the case of pianos, there have been books written on just how to mic a piano.  As you add microphones, you make the isolation described above that much harder to achieve.
  • If the room acoustics are bad, or there is too much "foreign" noise, even close miking may not result in a good recording, particularly if the microphones are not really close to the sound source of the instrument, or you are trying to capture the sound of a group of instruments with a single microphone. You may well discover that you cannot get a good recording.  After all, acoustic instruments are just that, and the microphone is picking up at least some of the sound of the recording space as well as the instrument.  There are various recording and post production techniques and equipment that can "clean up" dirty tracks but all of them leave various artifacts which may well be worse than the original recording, and most of them take a lot of trial and error to apply successfully.
  • The successful multitrack recording of separate tracks at different times, while allowing for better isolation and the ability to do individual track retakes, requires musicians with experience playing while listening to the previous tracks on headphones. This can be particularly problematic for recording the first few tracks, where the musician is essentially soloing, while imagining what the rest of the band will sound like.  Many musicians find this difficult to do successfully without a lot of prior experience.  In any event, the recording will probably loose the "vibes" between the musicians that make for a memorable recording.  Possibly not as important with pop music, but vital with good jazz, and in many cases steelpan.
  • The successful post production mix and processing can take far longer than the original recording.  In fact problems with the original recording that were not noticed during the recording process may require doing retakes of one or more tracks.
  • It is very easy during the mixing and processing process for the ears to become fatigued.  The mix that sounds perfect tonight can sound awful with the light of a new day.
  • It is vital to have good monitor speakers and amplifiers during the mixing process.  Otherwise your mix may well be compensating for your poor monitors, and sound bad when played with a better reproduction system.  (This applies to orchestral recording also, but since it s common to "process" the individual tracks of close miked multitrack recordings more than orchestral recordings, it becomes more critical when multitracking.)
  • It takes far more equipment which takes geometrically longer to set up and adjust if you are close miking a session with any significant number of microphones.  Close miking can greatly increase the costs involved, either for purchase or rental. 
  • Finally, if you spend significant time checking the individual tracks of a take and readjusting microphones or equipment, the musicians may loose any vibe or spirit at the session between takes.  Tired, bored musicians do not usually make for good music. 

 Most recordings of "pop" music have been close miked and multitracked, since at least the mid 1960's.