Dual mini ear mics for measurements...

Discussion in 'Calibration Equipment' started by Sonnie, Apr 27, 2017.

  1. Lanion

    Lanion Member

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  2. tesseract

    tesseract Senior Admin
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    Very cool, thanks for that, Lanion!
     
  3. Sonnie

    Sonnie Senior Admin
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    Interesting info Lanion... thanks!

    And welcome to AV NIRVANA
     
  4. aackthpt

    aackthpt New Member

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    Funny to find this thread, as I started to go down this rabbit hole a few years ago. I think I was thinking of it both as a room measurement method and as a way to make binaural recordings on the cheap. I'd have to see if I can dig deeply enough in the archives to see what sort of microphones I was thinking of using.

    Speaking of which, one of the Stereophile CDs back in the day had some Formula1 recorded exactly this way, with ear mics. Yep here it is, it's their test CD 3, track 15. https://www.amazon.com/Stereophile-Test-CD-3/dp/B0000049XR
     
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  5. Matthew J Poes

    Matthew J Poes Staff Writer
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    Binaural recordings are always made with ear mics as far as I know. That was a cool test track. Sounded disturbing real.

    REW can’t be used for two channel measurements because the second channel is only accessible via loop back. For all practical purposes it’s not a 2 channel recorder. I asked John if he planned to add that and he said yes but not soon the only interim fix is to take measurements with Two instances of REW open and then have one in the mode where it looks for an external test tone.

    My purpose for dual mic measurements is room characterization. I wouldn’t be shocked if that could be used for dsp processing of the speakers but I am certain DIRAC and other similar corrections cannot make use of that information. It can use multi mic averaged measurements but that’s also what it does with multiple measurement locations. During the beta phase we tested this with a mixer into a usb mic interface.
     
  6. Matthew J Poes

    Matthew J Poes Staff Writer
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    http://www.bnoack.com/index.html?http&&&www.bnoack.com/acoustic/bass-ratio.html

    Look at IACC for an idea what I wanted to do. I still plan to give this a try. I just need to get accurate measurement mics in a matched pair. Not cheap. I’m seeing of cross-spectrum would match a pair for me. I will not be using USB mics as I want to be sure there is just one clock in the AD converters. The measurement is looking at timing differences in delayed energy so the mics can’t have any timing differences due to clocks not being synced, which they wouldn’t be with usb mics.

    This can also be used to set speaker locations more accurately.
     
  7. Allen Rumbaugh

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    I have read and reread your posts here. Am I understanding it correctly that you want to bring in your outer ear into the measurement window? It appears that the mics are mounted facing outward in your ear canal. I just don't see how that is a benefit. I use this measurement mic http://www.earthworksaudio.com/microphones/m-series/m30/ it is hard to fit that quality in your ear. I am used to using Spectrafoo but REW looks like it will do the same thing, that is average multiple pickup points in the room. I would be very curious to see the difference in the measurements between the in ear mics and the m30 at multiple locations.
     
  8. Matthew J Poes

    Matthew J Poes Staff Writer
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    The M30 is one of the best mid priced measurement mics on the market for sure. I used to have one myself but sold it a few years back.

    I’m not personally interested in in-ear mics but it sounds like Sonnie and others are. I have interest in dual mic measurements to characterize the spaciousness/soundstage of the space. It’s more an experiment/curiosity as IACC is a spec for performance spaces and not home theaters.

    I think the interest in the dual ear mics is more a belief it may do a better job measuring what we hear. There are a number of researchers doing work like this, as well as a few proof of concept products that used this approach.

    REW does average and is in fact the approach I and others use to get the average response of the room over the entire listening area. That would serve a different purpose since timing information and phase are lost in such a measurement.
     
  9. AudiocRaver

    AudiocRaver Senior Admin
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    Playing catch up here.

    No news, of course, and it has been referred to already, that the HRTF (hearing response transfer function) is a big factor with in-ear or on-ear or around-the-ear ANYTHING.

    Interesting to me is the fact that with regular loudspeakers (or with hearing in general) the HRTF (via the outer and middle ear) is in the chain of what we are hearing all the time, in fact serves a role in the brain's creation of imaging and a soundstage (what direction did that sound come from?),,and with headphones or IEMs it is not, or at least is to a much lesser degree. HRTF is the bridge between speakers and headphones, it compensates a headphone's response to make its measurement have some equivalence with a speaker's measured response, and explains why a flat headphone response (mic at the ear drum) will sound different from a flat speaker response (mic in a free field).

    As pointed out, an in-ear mic would have to be really tiny and located in the plane of the ear drum to accurately capture sound like the ear.
     
  10. Matthew J Poes

    Matthew J Poes Staff Writer
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    Well I'm going to revive this thread because I've gotten myself into the rabbit hole that is David Griesinger's body of literature. I took a break from measuring headphones and trying to understand the source of the errors, it was pretty easy to figure that out, and decided to see what else I could use the EARS for. First I used it as the microphone for a video recording of my room as I walked around making sounds to see if it gave a cool effect. As it was Binaural with an HRTF, it should have given a perceived 3D sound and it did. Very cool!

    Of course, that wasn't really a scientific study of any kind and there was nothing all that useful there so I decided to instead take 2-channel measurements of a room to see if I could begin to detect LF ITD, per David's work on LF spaciousness and listener envelopment. This has been hugely challenging, far worse than I thought, but... a) I'm making progress in actually measuring a rooms ITD by frequency band, and b) I am successfully making binaural measurements of a room, but I cannot use REW or any of REW's test tones to do this accurately.

    What is so cool is that the elusive measurement needed by all of us is a measure of what we hear, not a single point measure of loudness. That is of limited value. Yet no measure like that currently exists, and certainly not one that is implemented in readily available software. This is getting closer. A cheap binaural microphone with an HRTF and a stereo recording of a log-sine sweep with reverb allows you to then create an impulse of the room and assess the rooms effect and interaction with the speakers on creating that sense of SS&I, spaciousness, envelopment, externalization of the source, etc. All things we can't normally measure at all.

    I hope to turn all of this into a series of videos and articles, I'm working through it all now. A lot of the other ideas I had for tech articles hit walls and this just seems way more interesting. I think the hardest part is taking these ideas, which are hugely complex, and distill them into a simple and easy to understand set of concept. I think we all care about SS&I, Spaciousness, and envelopment, but I think the average person doesn't understand that they care about it. People don't want mono-sound, they know that, but yet the understanding of source azimuth is totally missing from an average persons vocabulary. That is the gap that we need to bridge.

    Wayne if this interests you as much as me, and you want to help, I can certainly use it. I have a bunch of presentations on REW and acoustics coming up over the next 6 months and I hope to bring some of this in so that I can begin to really simplify these ideas and aid in writting the tech articles. I'd like to get the first of the articles out before the end of July.
     

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