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February 1, 2010

Recording didgeridoo for Kosmopterix – part 5

Microphone placement!

If I had to point out only one chapter about recording, this would be it!  It refers to recording didgeridoo, as well as any other instrument. I cannot stress enough how important role microphone placement played in recording Kosmopterix. Let me give you an example. For Lake of Awareness I was searching for didgeridoo and microphone placement for one week. I could do around 70 test recordings in one day. It takes a bit more than eight hours, breaks not included. After this one week of search, Lake was recorded in 7 takes, I think. That is one hour.
Another perspective is that buying expensive equipment is nonsense if you won’t take time to find the sound. Why? Because microphone placement changes sound so drastically that it can make a single mic singing like a shiny star or murmur like a mud – we don’t discuss tastes now – it is up to your vision what you look for. When you have more mics, then this effect is amplified.
We will go through this process in two steps.

Step 1 – Placing the didgeridoo.

It now goes without saying that your recording room is treated in some way, prepared for the incoming sound. As mentioned before, you can record didgeridoo in relatively small rooms if they are treated well – frequency and reverb-wise.  But if you have a small room, your sound will be very sensitive to any movements. You will be able to notice the difference from even few centimeters of change in didgeridoo placement.

First, lift your didgeridoo off the floor. The sound will be much clearer. When we recorded, bell of the didgeridoo was some 35cm elevated.
Second, put some absorption underneath the bell of didgeridoo and, if possible, the mics. We had 10cm thick 60X60cm square of rockwool for absorption. Notice the difference of sound.
Third, most complicated, get some help of great ears for didgeridoo. This person has a very demanding task in both physical and mental way. This brave person needs to:
– take the bell of the the didgeridoo while you play some characteristic part of the song to record
– lift it of the ground on the height where stands hold the didgeridoo,
– put his/her ear on the distance which is similar to the distance of the “main” mic – for me it was around 35cm
– move it, at the same time with the absorption underneath the didgeridoo, around the room to find a sweet spot
What is a sweet spot? Well if you like bitter, it might be a bitter spot for you, anyway it is the spot where your didgeridoo sounds the “best”. By “best” we could say it is a perfect blend of articulation, clearness, kick- bass, fullness… Once you decide which spot it is, try to stick to it unless you realize you can’t place the microphones properly.

Step 2 – Placing the microphones.

At this point I had some troubles which we will try to shortcut for you. My situation was that my didgeridoo was dancing a little bit after I thought I have put it firmly to my didgeridoo holder made of chairs, boxes and other stuff. If the didgeridoo moves between the points in time when you measured your microphone distances and recorded the sound, you are certainly doing something, but it is hard to name what, and it is most surely not finding the best microphone positions. When I realized it was happening to me, I got to the nearby railway station – in the department for repairs. I kindly asked, and kindly got, two steel plates heavy enough to anchor a house. I had arms the length of orangutan after I brought them home, and it was only for a few hundred of meters. I welded the bars with half circular holder for the didgeridoo, on screws, and I welded some bolts on the plates so that I have didgeridoo anchors that I can dismantle and put in 2D world. This really helped a lot, as now didgeridoo had no chance to move. This is how the stands look like;


I have a new method of making stands, which is simpler and lighter, but not as stable, I use it for live performances. This method is based on common microphone stand;
These stands really helped me and I finally managed to make good test recordings.
What I realized to be my biggest thing to solve is phase problems.  I wanted to record with more mics on different distances so I can get more sound, in all senses, but this is what can cause cancellation due to different phases in which sound reaches microphone.  It is especially problematic with basses. The usual three to one (ratio of mic distances – read more for example at http://www.roadogz.com/stories/downunder/speakerstostage3.htm ) did not help me  a lot, and I trusted mostly my ears  all the way through the recording.
It is a bit difficult to describe how phase problems sound, it is like a strange hushing in the recording which you hear as difference between one microphone sound and more microphone sounds at once.  It can reflect in lack of clarity, power… but you will hear it and you will know. I put here two examples from tests before recording.


It is from a song Lake of Awareness. Mix of three channels, one front microphone and two stereo behind. I did more test songs and sounds, but I chose this now, and the reason is that on the faster parts I could hear better how clarity and articulation were kept, and still there is enough kick to hear what happened to it. These are not two most drastic examples, however they suit our needs fine. Notice how it seems that there is much greater loudness difference between the two than it actually is. RMS loudness difference between the two files is only about 0.3 dB.
What I also looked for in this recording was to get a bit of an end bell sound, which in a way is didgeridoo sustain, and I got it to a certain extent. This recording was done with only three microphones. Royer R122V (via Thermionic Culture Earlybird) at around 32cm distance, and a pair of Schoeps MK2 AB stereo position, via Forsell SMP-2,  at around 57 cm from end of didgeridoo. Conversion was PrismSound.

Now three microphones with a didgeridoo can already give you a quite a hassle, but what about 8 microphones and where to place them? How to start?  Look at this beautiful picture.microphones
First. Start with one mic. Try to capture full detail from didge, but also with nice bass. You can’t do everything, but try to capture the most!  For me it was usually around 35 cm, right in front of the didge. For me articulation is more important than bass. For me it was always ribbon mic, but LDC or SDC could also work. But for you something else might work =)
Second. We make a triangle. Two more microphones, stereo pair, around 65cm distance, half a meter apart.  For me those were SDC mics-Schoeps MK2.
Second – variation – I recorded some of the songs with NOS technique (same as ORTF, only right angle between the mics)

–          Here we have three mics and it is time to adjust their phases

Third. Deltoid. One more microphone in the middle of the stereo pair, at the same distance from the didge as the two of those- so we don’t have to think about phases here, only adjust it a little bit if we don’t put it precisely enough for the first time.
Fourth. Bass microphone- 5 cm, or less, close to the opening. Ribbon or ldc or sdc, but so that it doesn’t disturb the sound. I’ve put my microphones always a bit down… –this one can also mess up phases, but it is easier to adjust than upper „deltoid“.
Fifth. Nose/mouth microphone – sdc od ldc, not very important, but better that it is a little higher than the nose so no direct air stream goes in it. This one does not mess up phases a lot, because it has quite weak signal from the didge, because nose/mouth is much more dominant here. If it is not so, put the microphone closer.

–          We’re now at 6 microphones, so let’s presume you have two more channels on your 8 channel converter/mixer

Sixth. Sound effect microphones – in a tube, or in a bottle, or in any acoustically interesting object. This object should change the sound so drastically that it is distinctly heard when mixed over „regular“ microphones. Try using PVC tubes that are in same note as your didgeridoo, or a fifth above/below, and hear what happens. You can also have many tubes and mix if you have enough channels available.
Seventh. Ambient microphones- omni polar pattern, one or two, placed in interesting rooms… far from the source. On Kosmopterix, only twice was reverb recorded. Once in the stone big hall next to the room where piano was in Kostrena, and the other time in huge Kino SC hall.

It is not essential to have all of these microphones, but if you have the possibility to do it, it definitely makes sense. What you can do here, and it is a time consuming but possibly rewarding thing, is to check on the rough mixes how different positions sound in different mixing proportions. That means that when you make a „cocktail“ from your sound maybe you can compensate the bass from the main microphone fully by bass microphone, and  maybe you don’t even need detail because you can extract them from stereo pair, and then you can concentrate on some special colour you’re trying to get. But  now this goes into the field of mixing. Funny thing about this process of making album is that all these phases (including microphone ones) are so interconnected, that in the end, in the mastering phase you can realize that you should have done something different in the beginning, like treated your room better. Acoustically.

What I would encourage you is to experiment, and give as much time needed as it takes until you are satisfied. To be really satisfied  first asks of you to get to know the situation. That means you can be satisfied with the first tested sound, but you might stop being satisfied after you hear the second tested sound. Comparison is the greatest tool of advancing here. But when it gets to the point that you are not sure of the difference, then it is probably not so important anymore. Keep yourself sane!

Good luck, and let me know about your results!

P.S. See how it went for us while recording 7 meter didgeridoo, with 8 microphones, in a 1000 seats hall.

in Recording didgeridoo

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