Stereo Mic Placement Software

Discussion in 'Tracking / Mixing / Editing' started by ATAK, Oct 24, 2005.

  1. ATAK

    ATAK Guest

    Hi There,

    Does anyone know if there is any software available that will either attempt to work out the most appropriate stereo mic placement after analysing certain criteria regarding the sounds source, or analyse audio produced from a recording and provide data which might allow me to "grade" different placements and make statements like "placement A is better than placement B because..."

    The reason I ask is that i'm currently researching stereo mic placement techniques as part of a Masters Degree and I want to do a "Man vs Machine" style investigation where I pitt my witts against a computer generated placement.

    Any info/links would be greatly appreciated.

    Thanks,

    Tom
     
  2. Thomas W. Bethel

    Thomas W. Bethel Well-Known Member

    That would be some very complex software because not only would you have to specify the EXACT microphone you would have to tell an awfully lot about the acoustics of the hall and about the artist(s) you were trying to record.

    Most of the microphone placements are worked out by experience (both in the hall and what microphone works best in a given situation) and by listening with the two best pieces of test equipment an audio engineer can own and that is your own two ears.

    There are such programs for speakers but the cavat is always "adjust for best performance using known material and your ears" So the same would have to be said about a program that predicts the placment of microphones. If you find such a program let us know. It would be interesting to see how it would select the microphone placement based on numerical data.
     
  3. Cucco

    Cucco Distinguished Member

    Hey ATAK!

    Welcome to RO.

    I think Tom B. has your answer, but I can maybe help provide an additional thought or two.

    First - where are you from and where are you doing your degree work?

    Second, yes, it is possible to do what it is that you ask, but there would be some serious compromises due to assumptions.

    What you would be looking at is a way of measuring the reverberation field in a given auditorium and using a "good" recording to determine where within that field the mics were placed.

    Then you would run a simulation by measuring the reverberation field in a different hall (or the same hall with different situations, as Tom B mentioned, it all changes when there are different musicians on stage.)

    Then, you would approximate that placement as determined from above by again determining the appropriate distance based on the reverberation field that you measured and place the mics in this new "scientific" method.

    To determine the reverberation field, you will need to determine the point in the auditorium (on all 3 axis) at which the late-reflected sound is approximately the same amplitude as the initial impulse. This is NOT the best place a microphone typically, rather, somewhere inside the reverb field at which a good balance of initial impulse and late-reflections is achieved.

    I imagine it could be done on a computer modeling system, however, I don't know of anything like this in use or existence. The defense contractor I work for (DSCI) does modeling and simulation, I'll check with them to see if they know of any system or program that can be adapted to do this or if they know if anything currently available.

    J.
     
  4. ATAK

    ATAK Guest

    Thankyou both for your replies...

    Was hoping for a quick win but had more than a sneaky feeling that I was asking the impossible (or near impossible anyway!)

    Let me expand a little... My first assignment as part of an ambient recording module for my course (studying at the London College Of Music and Media in England by the way Cucco) is to "research stereo microphone techniques and their application to live recording of acoustic instruments". The basic premise is that we research mic placements and then produce a number of ambient recordings, employing the techniques that we have studied.

    I am going to research 2 or 3 standard placements, record an ensemble using each technique and then "blind test" my fellow students to see if my research backs up the actual recordings. An idea I had to spice it up a bit was to see if I could get a computer generated placement recorded to prove (hopefully!) that my ears are better as I can process all the environment variables. Obviously that doesn't seem possible with an application but I do like your idea Cucco about measuring the room to gain an insight into the theoretically perfect placement.

    Ok, now the hard bit... I have access to ETF and have analysed rooms for RT60 and frequency response etc. before but i'm not sure I know how to calculate the reverberation field (even after reading your post a couple of times- sorry Cucco!) or what theoretical place in the room would provide the best recording.

    Once i've read round things a bit more and got to grips with the theory myself I should have more of an idea where to go from there.

    Thanks a lot for your help/advice, it's much appreciated

    Tom
     
  5. Cucco

    Cucco Distinguished Member

    Hey Tom -

    Good info. I'm glad that you're putting so much effort into the live recording aspect of the course. So many people in these types of courses really don't pay any attention to live recording as they assume they'll always be in a studio...

    As for measuring the reverb field - you could simply create a pulse on the stage itself and use various microphones to determine the place at which the initial sound and the reflected sound are the same. So, in short, if you were using software to do this, you would see in a waveform representation, the initial impulse. Then you would (milliseconds later) see the delayed attack(s). If you can move the mic in such a way that both the initial and the first delayed attack of significant value (usually your first late-reflection) are at equal amplitudes, then you have reached that point.

    However, as you point out, this is a futility and really not worth delving into much more. It would be interesting if you had the free time, but I don't know of too many engineers are going to use any kind of software to tell them where to put the mics.

    Although, if it gets much worse than the current state, where Waves plugins and DAWs are the order of the day and no one really knows how to record any more, then this kind of software might just be THE key to the future of live recording. Bleek, eh??

    J.
     
  6. recordista

    recordista Active Member

    Image Assistant

    I'm surprised nobody's mentioned Theile & Wittek's Image Assistant which will tell you a lot about the "view" a particular mic arrangement will provide.

    It will help if you have at least a passing familiarity with the work of Theile and/or Williams. Start with The Stereophonic Zoom and Multichannel Natural Music Recording Based on Psychoacoustic Principles.
     
  7. ATAK

    ATAK Guest

    Yeah that looks really good. It will certainly help me quantify my findings.

    Thanks a lot, may need to post a few questions later but will certainly try to get my head around their research first.

    Thanks agan,

    Tom
     
  8. Cucco

    Cucco Distinguished Member

    Re: Image Assistant

    Kurt -

    EXCELLENT post. This should be required reading for ANYONE doing what we do (and then some!) Though it (the software) doesn't do exactly what was being asked, it's still an invaluable tool.

    I'm going to make your post a sticky and call it "Required Reading"

    J.
     
  9. ATAK

    ATAK Guest

    Don't put it as a sticky yet all my fellow students might find it and it will de-value my research!!

    Lol... no those links are ace i'm printing the pdf's as we speak

    Thank you all

    Tom
     

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