Acoustic Recording Techniques
Audio production is a giant field with so many possibilities. Music recording these days can break down into two main categories digitally (midi based systems) and analog ( physical based instruments). Electronic music is basically anything that creates sounds synthetically or triggering samples such as a midi device. Even though computers have become the centre tool of our recording studio, knowing some acoustic recording techniques is very important. That leads us to our physical instruments, in particular acoustic instruments. These are instruments that resonate to create some kind of pitch such as a flute or a guitar.
How do acoustic instruments work?
All acoustic instruments consist of two main parts. The first part is the resonator of the acoustic instrument. This part vibrates or resonates when energy is applied to the instrument. The size of the resonator will determine the range of the pitch it creates. The other part is known as the driver. The driver applies energy to the resonator. This can be a drum stick or even your hand.
Acoustic instruments fall into 3 categories. The first category is percussion. Percussion instruments are anything you hit like a snare drum or a cymbal. The second category are strings. In a string instrument we pluck a string ( the length, tension and mass determine the pitch). The vibrations propagate through a connecting device such as a bridge and the body resonates amplifying the sound. The 3rd category are wind instruments. Air is applied forcing a reed or mouth piece to vibrate. These vibrations resonate through a series of piping or wooden casing.
Understanding how the instrument works that you are recording has a great importance when miking a instrument. An acoustic guitar has many different characteristics then a saxophone. And depending on where you place the mic on an acoustic guitar will sound drastically different.
Acoustics of a room
When setting up microphones its not just about the mic and the instrument. It’s also the room you are recording in. If I record a singer in my living room it will sound very different then if we record in a bathroom. This is because you have the direct signal from the instrument hitting the microphone, but also all the reflections from the sound bouncing off the walls. When these sounds reach the mic at a slightly delayed time, the delayed signals plus the direct signal is summed (added together) as a result the sound changes. This is something called constructive or destructive interference or better known as comb filtering.
So to combat this recording studios use iso booths that absorb the reflective sounds. This is great for certain things but of you want to capture a natural room sound then it’s not ideal. So what you can do is place the instrument or the player in different parts of the room you are recording in. Just moving the singer 3 feet to the left or tilting the amplifier can have a great impact on the sound you record.
Acoustic Guitar Mic Placement
Lets use an acoustic guitar to talk a bit about recording techniques. Constructive or distractive interference can also come into play when we’re using multiple mics ( recording in stereo). So to combat this which is also known as “phasing”( two signals being summed together at different points in their cycle or phase), we can use coincident techniques the xy mic technique or mid side mic technique. Coincident mic techniques use stereo mics set up at the same place in space, so in theory both mics will record the same signal keeping it in phase.
Try to set up the mics using an xy mic technique a foot out from the guitar aimed between the sound hole and the 12th fret, this is a really good starting point for acoustic guitar mic placement using a xy mic technique.
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