Hello everyone,
As you know, when recording an acoustic ensemble on location (also in studios), it can be sometimes difficult to decide exactly where to place a microphone array and how to setup the distance and angle between microphones correctly for a desired stereo width and localisation characteristics. To support sound engineers and audio students, we at the Applied Psychoacoustics Lab (APL) of Huddersfield University, UK developed a free app called MARRS for an interactive stereo mic technique simulation. It has an object-based GUI which visualises perceived positions of sound sources for a given microphone array configuration. It is an interactive tool where you can select the number of sources and position them anywhere on a virtual stage (both azimuth and elevation) and set up a preset or customised mic array at certain distance and height. The perceived position for each source in reproduction is visualised interactively as you change the mic configuration. MARRS is also an intelligent tool that can automatically configure suitable mic spacing and angle for the user's desired stereo width. This is done in a way that you can choose a configuration anywhere between 100% coincident and 100% spaced. So MARRS is a useful app for preparing your recording session and also for a sound recording education.

You can download it free from either Apple or Google app store by searching MARRS. Below are the links to the app and a quick start guide and an AES paper that describes the psychoacoustic principle for the algorithm used in MARRS.

- Apple iOS: https://itunes.apple.com/app/id1295926126

- Google Android: https://play.google.com/store/apps/d...marrs&hl=en_GB

- Quick start guide: http://eprints.hud.ac.uk/id/eprint/33675/

- AES paper: AES E-Library » An Interactive and Intelligent Tool for Microphone Array Design

The current version is only for 2-channel stereo, but future updates will include a 3-channel version and a web-audio version with binaural and room simulation.

Hope you find these useful. Any feedbacks are appreciated.

p.s. Actually there are some minor bugs on the current iOS version (graphical issues) and we will address them soon, but all the main functions still work as intended. No known issue with the Android version so far.

Hyunkook Lee
Leader of the Applied Psychoacoustics Lab
www.hud.ac.uk/apl
University of Huddersfield

Great app. I’m using it to help me with a recording I’m doing Sunday. I’m finding it very useful for deciding what type of mic placement to use.

I just put it on my phone (Android) and will be studying it. Do you intend o increase the types of mics?

Never mind, I found that you have "all" the mics represented.

As I mentioned when I spoke with
him at AES, it would be great to have
a center pair (eg ORTF, Blumlein, NOS)
PLUS near-spaced pair of e.g. omni's or other--( Variations of Boojum-Norman or
Faulkner (near-spaced hypocardiod pair
plus omni pair)).

Besides all the variations of 2 pairs in a line, it would be great to be able to move the center mono/stereo pair forward to create a variety of "Decca Tree" configurations.
Thanks,
Bill

PS Reportedly this app utilizes more
up-to-date/accurate psychoacoustic data than used in previous tools.

Downloading now, keen to check it out.

It was nice to meet you at the AES! And thanks for this suggestion. This might not be as straightforward as I initially thought but can do some research into and make it happen in the future ; )

Yes there are all popular polar patterns included. We can include more presets though : )

I, too, would love to see this - I'm sure it makes for a much more complicated calculation, but it's an area of interest for a lot of folks here.

Why no ms array ?

MS technique requires a decoding process but the current mic config view only deals with L and R channels. But ultimately, the resulting L and R from MS decoding are the same as an XY pair with a certain angle and polar pattern depending on the polar pattern of the mid microphone and M/S ratio. So the "result" of the MS decoding can still be simulated using the current app. We will consider including a dedicated MS decoding option in the future.

With that in mind, you could easily build a few MS variations into the list of presets and treat them as their decoded versions. So along with ORTF and XY and so on, you could have presets for:

1) MS with cardioid M at 1:1
2) MS with omni M at 1:1
3) MS with bidirectional M at 1:1

So if (1) above was chosen (cardioid MS, 1:1) it would open a preset for the equivalent coincident pair of hypercardioids at 120°. If (2) was chosen it will open a preset for the equivalent coincident pair of cardioids at 180°, and if (3) was chosen it will open a preset for the equivalent pair of bidirectionals at 90° (a Blumlein pair).

Those who are not familair with the MS equivalents will find that helpful...

That should certainly be possible. Thanks for the suggestion. But I think it won't be too difficult to include the actual MS decoder. It'd be useful for educational purpose too. We will work on it for a future release : )

Imo that would be very useful and educational.

To be able to see what happens when you change the M polar response, S level and elevation sliders.

Absolutely, to see those things change with an MS pair would be wonderful. Even as it is, after an initial play with it I shared it to a number of audio educational forums and similar. I think it’s a great visualisation tool for audio education.

If there's anyone here using the 'Stereo Mic Tools' app effectively ie: https://apprecs.com/ios/572383335/stereo-mic-tools
Stereo Mic Tools on the App Store
Stereo Mic Tools by Engineered Stuff

.....I wonder if you'd be kind enough to guide me through the section where the phone's camera is used to assess the width angle that the ensemble occupies on stage (directly in front of the mic pair), and this is then used to inform mic spacing and width to ensure congruence of stereo recording angle (SRA) ?

There's a similar one made by Neumann: Neumann Recording Tools |

.....but it lacks this "use your onboard phone camera" facility to calculate SRA that the Stereo Mic Tools app has inbuilt.

I use it a fair bit. Here’s what I know about it and how I use it.

Start by holding up the device so it is as vertical as possible. There should be a blue vertical line through the centre of the screen. An angle will be displayed next to it, in the upper part of the screen just to the right of the line. It could be any angle at this point in time but it needs to be 0°. It is zeroed by pressing the ‘zero’ button in the upper right of the screen. It’s not really a button, it’s just the word ‘zero’ written in relatively small blue letters, and it can be impossible to see depending on what image the camera is showing.

After tapping on the word ‘zero’, the angle displayed next to the vertical line will read 0°. Now simply turn the device on the axis created by the vertical line and it will show how many degrees you have rotated to the left or right so you can judge the width of the ensemble from the device’s point of view. As you rotate it, at a certain angle in the rotation the vertical line will turn green and also gets a bit thicker. This is the point in the camera image that will represent 75% of the stereo width. If you keep going past that point the line turns blue again until you reach the 100% width point, after which the line turns red. Anything in the area where the line is red will be hard left or right (depending on which way you’re turning!).

The 75% and 100% marker angles are based on whichever microphone width, spacing and polar response you have chosen - and those angles are shown at the bottom of the screen. As far as I know, the Performer Angle section cannot set those factors for you. So it’s a matter of back and forth stuff.

Here’s an approach I’ve taken lately where I’m using a matched pair of MKH800s on a stereo bar and don’t have a lot of time.

I start by putting the two microphones side by side, pretty much next to each other, facing foward, and in whichever polar response I think is going to be most appropriate based on surrounding sounds, etc. Monitoring through my Etymotic ER4 canal phones (excellent isolation) plugged into my Nagra 7 (which is hanging over my shoulder and connected to the mics), I move the stand around like a selfie stick (up/down/back/forth) until I find an appropriate balance of direct-to-reverberant energy and also a decent sense of ensemble. That lets me find a good starting distance and height - because you need those two things sorted before the app can make any sense.

With the distance and height sorted (close enough to start with), I’ll whip out the app and go to the Performers Angle section so I can see the angles where I want the 75% and 100% points to be - from the microphone’s distance. Then I find a combination of microphone angle, spacing and polar response to give me the required angles. After that, I’ll use the Bombsight section to set the microphone angles appropriately.

There are zillions of possibilities of spacing, polar responses and angles that will give the desired 75% and 100% angles, of course, so the choice always includes considering extraneous sounds (I’m not always in concert halls), how much mono compatibility I’ll need and so on.

Thanks Greg, that's an excellent and most helpful outline you've given here ! As you suggest, it is a bit arse-about, in terms of assuming that mic type/spacing/angle is predetermined, when in fact you'd tend to decide on that after making Performer Angle measurements ? However if I attend rehearsals there's usually enough time for the necessary to and fro-ing.

Is the 75% measurement sufficient to give good image spread in speakers....or is the 100% better in that regard ? The bomb-sight grid is excellent for working out the angles in short time....for that alone it's unsurpassed ! I still won't leave the measuring tape at home, especially for wider spacings with Omni mics.

I like that your mic placement method still relies on in-ear (ER4) empirical judgement for best sound, before going to the app for the optimal widths and angles: the best workflow possible

Thanks again for the very clear instructions and background info....much appreciated, I'll give it a go this week with a local choir !

Out of interest, have you tried the free Neumann equivalent, cited in post #15 above ? Despite not having the camera performer angle feature, it offers easier adjustment of the mic type/angle/spacing parameters...the 2 could work well in tandem ?

In my iPhone the app constantly crashes and I don’t get to the screen, where I can take a picture.
Ronald

There's been reference to 2 apps here: the Neumann 'Recording Tools' and the 'Stereo Mic Tools'. The Neumann has no picture capture ability, only the latter one can do that.

In Stereo Mic Tools, you touch the very small, grey, text in the centre at the lower edge which reads "Performer's Angle" to activate the camera, if you haven't done that ?

Maybe you need to do a system update to the latest IOS for your phone ....otherwise I can't understand the crash behaviour

It really depends on what’s being recorded. For me, a large orchestra, choir or similar ensemble is okay at 100%, but a string quartet sounds too weird that way and I’m more interesting in about 67% (2/3). Some things sound better letting the outer extremes go beyond 100% in order to keep the bulk of it around the 67% region. If I’m recording and filming at the same time, with social media being the destination, I might set the image width to suit how it appears on video.


I’m very much about taking strategic and methodical approaches to this stuff, making clear distinctions between what is objective and what is subjective. That partly came from years working all night sessions in recording studios and all night live sets, where it’s 4am and you’re struggling to stay awake but have to set up to record drums or something. Reducing as much of the process as possible into step-by-step methodical approaches means you can work on auto-pilot and get the job done (thank you Sherman Keene!).

Also, I really hate it when the best advice some experienced engineer has to offer a novice is “just use your ears”. Really not helpful and just basically lazy, IMHO. So the novice rolls up to his/her first choral recording with a pair of mics, some cable, a field recorder, a pair of headphones and a pocketful of “just use your ears”. LOL! There is so much helpful information that can be given long before it’s time to let your ears be the final arbiter - which they should always be.

Most of my recent recordings (the endangered music of SE Asia) is of small ensembles (one to four people) sitting on the ground performing. For those recordings I don’t need a tall stand and can take a different approach. I’ll still use the first part of the process (both mics side by side to find the right distance and height) but then loosen up the mics on the stereo bar so I can hold one in each hand and slide them along and rotate and angle them as desired while listening. That’s possible in those situations because I’m using a Nanostand and so the mics are within arms’ reach. Once I get the mic placements sorted, I lock them in and get on with it.

The interesting thing is that with both approaches I rarely ever end up with any of the standard configurations (ORTF or whatever). They are, after all, just presets that can make good starting points.


I do use them in tandem!

I find the Neumann app is great for determining ratios of mono compatibility and so on due to the way it shows the balance of time and intensity differences for any given set up. But that’s normally when I’m planning in advance to get an idea of what technique I would be leaning towards on a certain recording. I had to record a series of taiko drum performance in Bangkok earlier this year with flying mics. My first approach, a variation of Faulkner’s side-by-side bidirectionals, was a disaster. That’s not a criticism of the technique but my own fault for not ‘reading’ the room correctly during my preproduction visit. So before the second performance I used a combination of those two apps and arrived at a pair of forward-facing cardioids about 52cm apart. Worked wonderfully well - although that’s not always the case. Sometimes I find that the method tested in the apps doesn’t work at all - which usually means I didn’t read the situation properly in the first place.

Once I’m on the ground, at the location, I’ll take the approach I mentioned earlier to find the distance and height, then I’ll put the mics into the stereo technique I thought would work best, then I’ll tweak from there. I find the Neumann app is more useful as an insight in advance.

I didn’t want to mention the Neumann app here because this thread is about the MARRS app, which I think is excellent from an educational point of view. I often play with MARRS, building ensembles and tweaking parameters to see how things change, and then also cross-referencing the same set up in the Neumann app to check for the balance of time and intensity differences. It really helps to provide a deeper understanding of how all the different things interact.

Good luck with the choir recording!

I've just downloaded the app and everytime I want to change something it close. Iphone8. Any updates ?