Making recordings automatically implies a play with technology. The sound you play enters a microphone, passes a large number of digital tricks and finally freezes in a data file that you can play back later. This game has a number of aspects:
- Recording room/location
- Microphone characteristics
- Microphone setup
- Sample rate
- Word size
What is the best location for recording? A studio? A concert hall? A living room? Room for discussion, but you have to have a choice first. I guess that there are not many people that are able to borrow the Royal Albert Hall on a daily basis. You will have to use the room that is available to you.
Just like many guitarists, I have a playing spot at home that might be suitable for recording too. My playing spot used to be the attic, currently it is a spare bedroom.
The attic used to be a good place to play, reasonably quiet and a nice temperature, not considering heat waves and blizzards outside. With respect to background noises, it is no top location. The boiler of the central heating makes its noises, the ventilator of the home exhaust is running all day and of course the washing machine and dryer have their rounds too. The most penetrating sound from outside is a tropical bird in the aviary of one of the neighbours. The funny thing is that this screamer reacts on my guitar playing with lots of hullaboo if I have my window open.
My current guitar room is fairly quiet and a lot more comfortable than the attic. I had to share the room with a home office for a while, so space is limited. I can muffle the background noises of the house by closing the door. However, because the children have been out of the house for years, the most annoying background noise now comes from neighbours and outside.
With the microphones close to the guitar, the effect of background noise is not too bad. Here you see the importance of a suitable microphone characteristic, responsive at the front, damping at the back.
As soon as you start considering the right type of microphone for recording classical guitar music, a discussion explodes that cannot be recorded by any microphone. Directional sensitivity is important, but what curve should you use? Are you going to use a single microphone, or a set of them in a setup?
The noise will diminish soon once you consider the necessary budget for all this fancy stuff, because good microphones cost good money indeed! Because I initially wanted to record guitar duos, my budget enabled the purchase of two workhorses, robust AKG C1000 condenser microphones with cardioid patterns. The AKGs provide for nice and clear recordings. The microphone has little extensions to change the pattern into super-cardioid, but I did not use that up till now.
If you have two microphones, you can use them in a particular setup. There are quite a few, A-B (just side by side, pointing at the instrument), X-Y (placed at 90 degrees, pointing away 45 degrees with reference to the instrument direction), ORTF (placed at 110 degrees, pointing away 55 degrees with reference to the instrument direction). These are setups for identical microphones, there are other variants for microphones with different characteristics. Every setup has its specific applications, instrument distance and room size play an important role with these applications.
I achieve nice results with an X-Y setup at about 50 – 100 cm from the guitar. The recordings have some space, but not an exaggerated stereo-effect. The results are a good start for post-processing with the computer.
The signal from the microphone needs to be processed into a recording. My Tascam DR100 is a perfect device for this. One of the actions of this device is sampling the microphone signal prior to analogue-to-digital conversion. Doing so, the sample rate is the number of times per second that the device measures the microphone signal for analogue-to-digital conversion and calculates the digital audio value. A sample rate of 44.1 KHz is the standard for CD quality digital music. If you choose this sample rate slightly higher, you will have some room (i.e. data) for post-processing. Therefore, I record my pieces with an 48 kHz sample rate.
The digital word-size determines the accuracy, the resolution of the analogue-to-digital conversion and the way back, the digital-to-analogue conversion. This resolution also determines the noise level that is caused by the conversion operations. Most CD recordings have a word-size of 16 bits, which means that you subdivide the complete signal range in approx. 65.000 steps. A larger word-size gives better post-processing options, so for my recordings I use a word-size of 24 bits.
Recordings at close range do not have a lot of acoustic response from the recording room. It is nice and clear, but a bit at the dry side too. Therefore, I add some reverb (quite a little), and I will not exaggerate this!
I have been working some time using these settings and techniques. I will try some experiments with post-processing (like compression and equalization) later. To facilitate these experiments, I make a raw recording first, I only cut useless sections (breaks, tuning etc.). Then I start post-processing with a copy of the raw material, enabling me to apply some new tricks if the need arises.
Then it’s time to apply the sound profile. Nowadays I use Wavelab Lite with the excellent Valhalla DSP plugin for the reverb. Reverberation is a university study in itself. I still have to learn to deal with that, but I’m on my way. I will come back to that at a later stage.