Different Microphone Polar Patterns
|Omni||Picks up signal all round|
|Cardioid||Picks up mainly in front (and a little
off-axissound from side and back)
|Hyper Cardioid||Hyper Cardioid|
|Figure of 8||Picks up front and back (with a little
off-axisfrom the side)
Many microphones have only one polar pattern. Some microphones can switch between the various patterns.
Cardioid (and hyper cardioid)
This is the most common pattern used for recording pop and rock, when
close miking instruments or vocals. Used when separation is necessary, or to avoid excessive
room ambience. Very close miking tends to create a proximity effect which adds bass. A pop shield is usually required on vocals. The off-axis (side and back) signal, though low in level, is not cut out completely and can add unnatural sound, especially hyper cardioid. Hyper cardioid may also cause problems with sibilance. Note that hypercardioid has a small amount of rear pickup.
Often sounds more natural than cardioid, especially if you want room ambience and separation is not an issue (i.e. the acoustic balance between performers is good and will not require rebalancing in the mix). Omni can sound better than cardioid and can be used when separation or very dry recording is required but requires more care. You may need to place the mic extremely close or deaden the room by hanging drapes etc.
Figure of 8 (bi-directional)
Often sounds more natural than cardioid, as with omni. Useful for two singers on one mic facing each other, or special techniques such as placing between a guitar amp and a reflective surface.
Mono or Stereo?
With multitrack recording several mono and/or stereo sources are processed and ultimately combined to create a final stereo mix. Often single vocals and many instruments are recorded in mono, the tracks are then
panned to varying degrees of left, centre or right in the stereo image. (NB: This is not
true stereo which represents the natural panorama of the sound as recorded by two microphones – see below – but it allows an enormous degree of control). Larger instruments or combinations are often recorded in stereo, the resulting track can either be balanced or panned to either side, or left in the middle of the final stereo image. If it is panned left or right the stereo image of the track will obviously become narrower as it is panned further to one side or the other.
The fewer instruments being used in the final mix, the more useful stereo recording becomes: if the instrumentation consists of acoustic guitar, congas and vocals, then the congas and acoustic guitar will definitely benefit from being recorded in stereo whether they are recorded simultaneously or overdubbed. Even if the sound source is quite contained and appears to be highly mono, the room ambience is always stereo and if you want to use it in the recording it is a good idea to record in stereo. Generally lead vocals are recorded with the microphone quite close in order to minimise room ambience, and the sound source (the mouth) is relatively small, so usually a mono recording is fine, though stereo mics could be used.
True stereo recording uses two identical microphones, usually set up in one of the following ways:
|Coincident pair||Cardioid mics placed together pointing out at 90 degrees|
|Spaced omni||Omni mics place apart . The distance depends on size of instrument or group, you need to experiment: too close and the stereo image will be rather narrow, too far apart and there will be a
holein the middle. I have seen some engineers use three or more microphones for a very wide image with no hole.
|MS (Mid and Sides)||Omni or cardioid mic facing forward, figure of 8 sideways with the two channels out of phase. (You can do this with the DirMixer plugin on Logic )|
When recording in stereo via a mixing desk, pan one channel hard left, the other hard right on the desk (unless the desk has dedicated stereo channel strips. Set the audio track object in Logic to stereo. This will record a single interleaved audio (wav, aif or SD2) file.
In addition to true stereo, several mono microphones or other audio sources (eg sound modules, electric guitar) can be panned to any position in the stereo image and combined using the stereo submix of the desk.
This method can also be combined with
true stereo. When recording rock and pop drumkits, it is very common to use several mono microphones on individual drums along with a stereo pair of
overheads. The overhead mics record the kit as a whole instruments, often emphasising the ride and crash cymbals along with a certain amount of
room ambience depending on their position.
Typical multi-mic drum setups:
|Stereo pair||Live sound, good for jazz. Not good for powerful bass drum and snare sounds|
|Stereo pair, snare and bass drum||Good for live sounding rock and jazz where snare and bass drum require beefing up|
|Mic on each drum||
Drykit sound. Good when level of individual drums must be controllable in mix)
|Mic on each drum and stereo overheads||Good for maximum control of total kit in mix.|
Although mono and stereo sources can be combined to stereo at the desk, it is usually better to keep them separate in Logic for more control over the balance at the mixing stage. Traditionally classical ensembles are recorded with a stereo pair, but
spot mics can be put on individual instruments to boost quiet instruments. It is important to pan mono sources to their correct position in the stereo image if combining with a stereo pair.