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  1. #1
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    Earthworks M30 vs ECM 8000 side-by-side test for Inguz DRC

    I took measurements today with both of the mics, using a Sound Devices USBPre audio interface. Very interesting results!

    The first chart shows the freq response of the left channel measurements (Due to differing sensitivities the sweeps were at slightly different levels. So I shifted the ECM8000 up about 4db for the sake of comparison).

    The second shows the phase response (built with the drc Octave scripts).

    The third shows the Test_Convolution of the normal filters computed with a flat target curve and each mic's calibration file (unshifted traces). The ECM8000 filter looks a lot like the mic cal file profile. (I am still suspicious/baffled about drc's use of mic cal files).

    The fourth chart shows the frequency response of the two mics -- ie a plot the calibration files. I had the ECM8000 calibrated by a third party and Earthworks provides a calibration file for all their mics for an extra $50.

    It's interesting to see that the ECM8000 does mostly OK in the lower freq, but not so well above 1KHz.

    Only had time to get these measurements done and have yet to do a listening test. One day I'll try same test with an Radio Shack SPL and also compare the Tascam US-122L to the Sound Devices USB Pre.

    muski
    Last edited by muski; 2007-09-28 at 06:58.
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  2. #2
    Quote Originally Posted by muski View Post
    It's interesting to see that the ECM8000 does mostly OK in the lower freq, but not so well above 1KHz.

    muski
    Very interesting! Thanks for sharing. Not a good news for ECM8000 users like me (and like most here I guess). I assume that the response in the treble would be more sensitive to the exact position of the mike than in the bass. Do you think this could account for some of the differences or did you manage to position them the very same?

    Anayway there is still something positive about it: this would mean that if I take the path of Audiolense to take measures and generate filters for below 200Hz correction only, I shall be fine. the more I listen to filters and the more I thnik I cannot live without the low frequency corrections, but that in the upper frequencies this is more a matter of the sound being different, sometimes better, sometimes not, depending on the music (definitly clearer and with more lisibility, but sometimes too much on the dry side...)
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  3. #3
    muski, so it is confirmed, without a calibration the ECM8k is almost useless

    Tell me one thing please, in the first pic, which calibration file for the ECM did you use?
    I hope it was none (zeros) so that I can adjust mine.

    Very helpful indeed, so we do have hi freq issue. I say we because I have the same recorded response with my ECM.
    Also I own Bryston 4BSST...could it be the cause hmm

  4. #4
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    Quote Originally Posted by muski View Post
    The ECM8000 filter looks a lot like the mic cal file profile. (I am still suspicious/baffled about drc's use of mic cal files).
    Almost exactly...like it was the target instead of flat...


    I see something similar with my mic-cal which has a gently rising slope from 5k upwards to 20k of about 5 db. I also see that reflected in the filter but too a lesser extent then in yours.

    peter

  5. #5
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    Quote Originally Posted by nuhi View Post
    muski, so it is confirmed, without a calibration the ECM8k is almost useless
    This gets more and more interesting. I sent my ECM8000 out as well to get calibrated. I'll post my cal curve as soon as I get it back.

  6. #6
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    Quote Originally Posted by Chinanico View Post
    I assume that the response in the treble would be more sensitive to the exact position of the mike than in the bass. Do you think this could account for some of the differences or did you manage to position them the very same?
    I used a mic stand and was very careful to get the tips of the mics in the same place. From the prep log file, it looks like maybe it was 1cm different in the R channel (though these plots show the left channel, which are the same).

    The M30 prep.log:
    Processing left measurement (m30left.wav)...
    Right channel seems to be the sweep
    Impulse peak at sample 444 (3.43m, 11.24ft)
    Deconvolution: left impulse done.

    Processing right measurement (m30right.wav)...
    Right channel seems to be the sweep
    Impulse peak at sample 444 (3.43m, 11.24ft)
    Deconvolution: right impulse done.
    The ECM8000 prep.log
    Processing left measurement (ecmleft.wav)...
    Right channel seems to be the sweep
    Impulse peak at sample 444 (3.43m, 11.24ft)
    Deconvolution: left impulse done.

    Processing right measurement (ecmright.wav)...
    Right channel seems to be the sweep
    Impulse peak at sample 443 (3.42m, 11.22ft)
    Deconvolution: right impulse done.
    muski
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  7. #7
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    Quote Originally Posted by nuhi View Post
    Tell me one thing please, in the first pic, which calibration file for the ECM did you use?
    The first graph is just the Impulse_Response_Measured, so there is no mic calibration applied (ie zeros). In fact, I can't figure out how to generate mic-cal adjusted graphs of the sweeps...
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  8. #8
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    R Channel

    Here are the same first three graphs for the right channel -- just to double check things.

    Freq response is very similar, though the phase plot is slightly different. Maybe the ECM8000 is actually ok in terms of capturing phase information.
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  9. #9
    muski, oh ok.

    While adjusting the curve to your new comparison I was wondering are those dBs on the phase response actually degrees or it's more like divided somehow?

    I'm asking because in the default ecm8000 there is a huge difference, like 3 times stronger correction in phase (they use 20, your shows 7 for example).

    Maybe this graph of yours is 3 to 1 or something when it comes to phase?
    I would want it to be 1:1, just asking if you know.


    And let us know how does it sing, you haven't commented yet, don't tell me you're not satisfied?
    Maybe at first you'll miss the 3khz bump and it may sound more polite and boring but when you get used to the real flatness it's great.


    Btw for those experimenting try this ecm8000.txt correction:
    0.0 0.0 10.0
    20.0 0.0 9.0
    23.0 0.0 0.0
    158.0 0.0 0.0
    200.0 0.0 0.0
    2000.0 0.0 0.0
    3000.0 0.0 0.0
    10000.0 7.0 -7.5
    15000.0 3.0 -4.0
    22050.0 0.0 -3.0
    Last edited by nuhi; 2007-09-28 at 08:50.

  10. #10
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    Quote Originally Posted by nuhi View Post
    muski, oh ok.

    While adjusting the curve to your new comparison I was wondering are those dBs on the phase response actually degrees or it's more like divided somehow
    No, it's degrees (-180->0->180). (BTW, I have no phase information in either of my mic cal files). It seems like these phase response plots vary a lot depending on the amount of smoothing done. I'll have a look at the other Octave phase plots.

    From the DRC documentation, it's not clear how much benefit there is to modifying the phase information. Also, it looks like you need to modify the .drc files to make sure all the MC flags are set correctly.

    From http://drc-fir.sourceforge.net/doc/drc.html:
    Starting from version 2.0.0 DRC lets you specify the phase for the target post filter stage. Phase specification should be placed after the amplitude specification and should be expressed in degrees. Following the example above:
    0 -40 0
    18 -20 45
    20 0 90
    20000 0 180
    21000 -40 90
    22050 -100 0
    If not specified a value of 0 is assumed. Setting a phase different than 0, i.e. flat, is useless within normal HiFi systems in almost all circumstances. Furthermore the phase specification is used only if the PSFilterType is L, else any phase specification is wiped out by the minimum phase filter extraction.
    Looking forward to doing some listening tests tonight!

    muske
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