I'm really enjoying a few things in life at the moment, one of them is absolutely contributing to audio projects as a sound engineer and constantly learning new things in that field, the other is my recent love of my new handpan!
So even though I'm still very amateur as a handpan player, I had a lot of fun playing around with three basic stereo micing techniques in the studio yesterday. So if you can ignore the errors in my playing - join me for an analysis of these stereo techniques on the handpan.
So before we get on with it, here is where you can listen to the recordings while you read ;)
Mics:
For each of these techniques, I used a matched pair of AKG C451b's. These mics are cardioid, single diaphragm SDC's, with a characteristically airy sound.
Processing:
The three clips each have the same processing: A small amount of compression and the exact same EQ. There is no time based effects like reverb or delays - I've kept the processing minimal so as to maintain the integrity of the comparison.
The Breakdown:
I started off with an ORTF pair,
What is it?
ORTF (or Side-Other-Side) is a stereo technique that was developed in the early 1960s in France. It consists of a pair of cardioid mics, capsules placed 17cm apart and mounted at a relative angle of 110 degrees. ORTF sits in a middle ground between coincident techniques and spaced pair techniques, utilising both level differences and timing differences to create the stereo image. If used correctly it has fair mono compatibility, and can offer the best of both worlds when considering A/B or X/Y setups.
Analysis:
My ORTF setup I think produces a beautiful stereo image, wider than the XY and not quite as wide as the AB, but depending on the production a really wide handpan image probably isn't necessary. It's picked up the low end rather well, the mics being close enough for the proximity effect to not be an issue. Even with the off axis nature of ORTF, the highs seem to resonate accurately, this is likely because the off-axis response of the SDC's I chose is quite good, a pair of LDC's would likely have a worse off axis response. The spacing between the mics has produced a more full sound when compared to the XY.
"Part of what is lovely about the handpan is the sense of immersion, and that only comes through subtle low frequency phase differences between left and right channels - exactly the kind of stuff coincident approaches aim to avoid!" - Greg Simmons
Summing this one to mono produces little loss in frequencies, as the minor spacing between the mics is not enough to cause comb filtering, and the mics have good enough specs (off axis response, cardioid polar pattern) to avoid producing a 'hole' in the middle of the mix.
Next I tried an XY pair,
What is it?
XY is a coincident technique (diaphragms as close as possible to each other), with the two matched pair microphones facing each other at an angle from 90 to 135 degrees. This coincident approach almost eliminates any phase cancellation issues when summed to mono, therefore it's the most mono compatible technique I used in this experiment. The stereo spread can be increased by utilising a greater angle between the mics. XY relies on level differences to create the stereo image, ignoring the timing differences of other techniques.
Analysis:
This technique seems to have captured the smallest stereo image of the three, I could have used a larger angle between the mics (I used around 110 degrees) to get a wider image. That being said I really do notice that the full resonant 'body' sound of the handpan is not captured as much here, I much prefer the sound of AB or ORTF with their timing differences. This I believe is because XY is only level differences, and does not have the 2ms or so time difference that gives a handpan recording a full sound. When summed to mono the XY technique shines, maintaining all of its frequencies as there is no phase issues, precisely because there is no timing difference between the mics. It has its place, but I don't think I'll be using it for handpan again! It just sounds thinner than spaced pair techniques.
Finally I hit up an AB mic positioning!
What is it?
The AB technique is a spaced pair, meaning that you symmetrically place a pair of mics either side of whatever you're recording. This spacing (3 to 10 feet) between the mics creates a timing difference (around 2ms) that is perceived as a stereo image when the mics are panned left and right respectively. This is an excellent technique for creating a wide and immersive stereo image, however it also holds the greatest risk out of these techniques of phase issues when summed to mono.
Analysis:
This is probably my favourite technique out of the three I've tried so far, and I'll continue to use it and refine it as I go. This technique is great for the handpan, as the larger timing difference for me really highlights to resonant sound of this instrument wonderfully. The stereo spread is also wider than both other techniques, and creates a real sense of presence because of that. When summed to mono the sound is still pleasant and reflective of the natural sound, however it loses the sense of presence I really enjoy and seems to get a slightly diminished high end as well.
One thing that I could have improved with this particular recording was to grab a couple of omni SDCs instead of the cardioids I used, this would eliminated the proximity effect and the low frequencies would be 'rounder', 'fuller', or basically more accurate!
Feedback:
Recording Engineer Greg Simmons provided me with some feedback and comments on recording handpan and my spaced pair/AB recording you can see in the video below.
"I think you got a really consistent balance between the hand slap, the notes and the handpan body in this recording. The instrument sounds like the same instrument throughout, which is cool"
He also gave me some advice on controlling the 'slap' articulation sounds of the fingers on the pan, which I implemented in the three technique clips!
1) Create a high frequency shelf that starts at 5kHz (0dB) and consistently ramps down over an octave to -4dB at 10kHz at which point it ‘shelves’ and stays consistent.
2) Add a bell dip that is 0dB at 10kHz, -1dB between 11kHz and 12kHz, and back to 0dB around 13kHz.
3) Create a low pass filter that is 0dB at 15kHz but then rolls off quite steeply so it is around -8dB by the time it reaches 20kHz.
In comparison to the AB video recording above in which I used my own LPF to control the articulation sounds, there is a subtle difference in the level and harshness of those high frequencies that I think Greg's takes under control a bit more. - Thanks Greg!
References:
1. AKG Acoustics. (2017). Retrieved from https://www.akg.com/on/demandware.static/-/Sites-masterCatalog_Harman/default/dw8153e218/pdfs/AKG_CutSheet_C451B%20Matching%20Pair%20Condencer%20Mic%20Set.pdf
2. Robjohns, H. (2014). Q. Does the centre of an image suffer with the ORTF recording technique? |. Retrieved from https://www.soundonsound.com/sound-advice/q-does-centre-image-suffer-ortf-recording-technique
3. WikiAudio. (2018). AB Stereo Mic Technique - WikiAudio. Retrieved from https://www.wikiaudio.org/ab-stereo-mic-technique/
4. PSW Staff. (2016). In The Studio: Stereo Microphone Techniques - ProSoundWeb. Retrieved from https://www.prosoundweb.com/topics/production/stereo_microphone_techniques/
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