Saturday, September 29, 2012

Dave Rat Blog - Up Down and Side to Side

San Antonio Texas and a cool hotel on the Riverwalk. Show day of the 4th gig of the tour leg. San Diego, Glendale AZ, and Denver so far with Dallas and New Orleans still ahead.

I continue to ponder the deficiencies in the methods typically used to setup and measure the implementation of live audio systems and question whether a truly accurate and useful method even exists. Primarily the aspect I am focused on has to do with the inability of measurement systems to adequately differentiate between comb-filtering issues occurring in the horizontal versus the vertical domains.

With two horizontally spaced sources, like our home stereo or a typical live sound system setup, the comb filtering that results is not really a negative issue to our ears yet common measurement methods will typically indicate the interaction from the output of the two sources as undesirable, not flat and a series of summations and cancellations known as comb-filtering.

With identical vertically spaced sources conventional measurement methods will measure the same issues from any single point as with the horizontal sources mentioned above, yet sonically  perception-wise to our ears, the sound is far from the same. Horizontally spaced sources covering the same area sound 'stereo' and so desirable that we strive set up sound systems this way, comb-filtering and all. With vertically spaced sources covering the same area we do not enjoy the perceptual benefits of that 'stereo' sound so all we are left with is determining whether the resulting comb-filtering is an issue or not.

Is vertical comb-filtering less important to our ears than horizontal comb filtering? Is that why variable angle line arrays are always vertical? Is horizontal comb-filtering desirable from spaced sources (stereo) and an issue from horizontal sources in close proximity? Yet with vertical sources in in close proximity, are our ears less likely to here the issues associated with the multiple sources reproducing the same signal?  If any or all of the above are true, then differing amounts of relevance would need to be attributed to comb-filtering issues depending on whether the sources are horizontally spaced or vertically spaced and also one the spacing distances as well.

Does the method you use to measure, calibrate and EQ a live sound system have the ability to tell you effectively "OK, these horizontal issues are no big deal and these horizontal issues are a big deal where as these same vertical issues are no big deal and these vertical issues are a concern."?

And on to sharing a few pics:

This blog is focused on the audio and adventure side of tour but a bit of love and recognition for my friends and the band who has me join them on these worldly adventures.

My view from FOH

It was great to see the band OFF! opening for Peppers in Los Angeles. Long history with old friends, yay!

And where I left off last blog was in Beirut, we then headed to Istambul and WOW! What and absolutely amazing city.  Truly magic and I can not recommend enough a visit there added to your adventuring dream list.

And doing Dave Rat seminars in cool places is so darn cool! Another group of wonderful sound nerds. Thank you for hanging out with me and being such gracious hosts!

Here is the Istambul gig

This was the last show with us for Ulf whom came to join us and assist with the stadium sized Peppers show. A true pleasure and honor working with you and see you soon I hope.

Finally, to sign off with a bit of curiosity, here is a pic I snapped out the van window as we drove into Tel Aviv

Oh my

OK, more to come and off to do a show in San Antonio, rocking!


  1. Wow! That last photo is kind of creepy!
    Istanbul has been on my bucket list for a long, long time now. I must make it there soon.

    While you were in Israel, did you go to the Dead Sea? When we were in Jordan, we went to a dinner there. The shore on the other side was Israel! The Dead Sea is the lowest point in the world!

    Missing y'all! See you soon!

  2. Could you employ some type of mic array (i.e. 2 mics 6" apart horizontally, with a third 6" above one of those), and use software to look at the differences between what the two planes are hearing? For instance, the two in the same horizontal plane would be able to show the effects of comb filtering based on the time differences of what they hear, and similarly with the mics in the vertical plane. It seems like you could overlay the readout of the horizontal against the readout of the vertical, and get a good idea of what sort of interactions you're dealing with. Just a thought...

  3. Theoretically yes, though a usable and practical form of what you describe has yet to exist

    1. In live sound measurement, no. However, the military has something similar in the works that seems awfully close to what I described. At the very least, it's an interesting read...

  4. >Does the method you use to measure, calibrate and EQ a live sound system have the ability to tell you effectively "OK, these horizontal issues are no big deal and these horizontal issues are a big deal where as these same vertical issues are no big deal and these vertical issues are a concern."?<
    Yes, Measurement should always be done as in combination with a design, and if you find things that are out of design they would be treated as bad, and hopefully minimized. Sound and combfiltering are not random but tied to physics so can be predicted and measured. There perception are however more random and tied to the individual. Measurement is also not random, but tied to finding what your looking for. Yes you can cheat the measurement program and its operator, but thats an invalid data/measurement and a human problem mostlikely knowledge problem.

    You answer your own problem Dave; sonically perception-wise to our ears, the sound is far from the same.
    Its a brain problem not a measurement problem. How your brain and the physics of your hearing system, percept things, are unique too you. You have been trained to think certain combfiltering are bad and others are not. Before we invent machines that can guess what we will think, it will just be a guess. Yes I belive that you can take 100 sound men and ask them what they think sounds good and make a lot of data on that, and produce an measurement methode that can show you an aprox of if they would like the sound of something. But it will be a guess. It will also be hard pressed to actually test different things untill we are able to adjust all parameters of summation in a speaker array and plane... maybe we are getting a little closer with multi cell speakers, where things sum at the listning plane not at the speaker...

    1. I believe that the ability of a measurement system to provide us relevant information is critical. I do not believe that it is unrealistic to seek a measurement system that takes into account the fact that we as humans hear phase differentials more accurately in the horizontal domain. I believe that the current measurement methods have some serious drawbacks and that in the not too distant future there will be advances that allow the measurement systems to provide more usable data in a less time consuming and cumbersome manner.

      To start with, a microphone that captures audio in a manner more similar to the camera would be a start.

  5. Hey Dave,
    Thanks, yes I agree. We have much to learn in the field of measurement, when it comes to: How do we use our measured objective parameters to something we can use subjective to make it sound better. Lucky we/there are people working to go that direction, and as you say in the not too distant future, we are able to take the next step up the ladder. As a teaser i can say that one example is: not that long ago there was a speaker system that really broke the market because people found it easy to mix on, especially "harder rock". If you analyze that system, there are parameters that can be transfered (directly with out too much fuzz or high end gear) to other systems (otherwise not liked by the same people) that gives those people the same WOW effect, and make it "easy" to mix on..
    By the way If you have any concrete Ideas you should share them with Jamie Anderson, he (and his company) are proberly the ones that recognize "physco acoustics" and that you have to use the "objective" data to to help translate subjective sound quality, the most.
    Cool camera by the way!

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