Recording an acoustic guitar without going direct is tricky. Always has been. Acoustics create a myriad of overtones and resonances with inflections originating from all parts of the guitar. This is the elegance of the instrument, but this blend of intonations- however easy for the human ear to process - is more of a challenge for an inanimate microphone.
First of all, record in as quiet a room as possible. Turn off overhead fans, swirling computer hard drives and other interfering ambient noise sources. Put some fresh strings on your instrument, yet be ready for the inherent initial brightness most new strings possess.
The type of microphone is key. Remember the two basic and most common flavors of mics: dynamic and condenser. Dynamic mics are tough and rugged and usually require no external power to operate. They can handle loud sound pressure levels and work as air pressure waves vibrate a coil creating an electrical signal. The Shure SM57 is probably the most popular dynamic mic on the market and is considered a work horse in the industry for recording electric guitar from an amplifier. However, for recording acoustic guitar, your best bet is using a condenser mic. Preferably a pair.
Inside a condenser mic, a charged plate - diaphragm - fluctuates with any change to the surrounding air waves which in turn creates a small electrical signal. Unlike dynamic mics, condensers require a power source to operate, usually phantom power which is a steady current sent to the mic from a preamp or mixing board or from a battery inside the mic itself. Regardless of the power source, condenser microphones have the innate ability to pick up high frequencies and are the choice for recording acoustic guitar. The price of a condenser mic runs from $100 up to several thousand dollars. Condenser mics have either large or smaller diaphragms. Try to stick with a pair of small-diaphragm condensers if you plan on recording a lot of acoustic guitar, since the smaller diaphragms can respond to fast, fleeting tones popping off your fingers and strings.
You can always record with just one mic, but if your budget allows, go with a pair of mics.
The temptation for the novice musician is to place a condenser mic directly opposite the sound-hole of the guitar. While this position certainly may have some individuality, it's best for starters to try to avoid direct placement as the resulting sound could be too booming along with a cut in high frequencies. Also avoid placing the mic too close to the guitar - most sources agree that 1 to 2 feet away is optimal. A spaced pair of mics is a great pattern to capture all the tones of an acoustic guitar in stereo. See Figure A.
Position one mic at about the 12th fret and the other around the bridge. With this spaced pair pattern you can mix the two mics into one mono track or one stereo track. Another option is to send each mic into a separate track and then to split the two channels into different parts of the sound field when mixing for cool effects- panning one hard left and the other hard right before recording.
If you only have one mic to use, try placing it around the 10th fret around 8 inches from the neck. You should always experiment with changing locations before you punch the record button.l
We will explore going direct with your acoustic guitar in a later article.
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