Alright folks, some quantitative comparisons of Audyssey XT32/MultEQ-X (Denon X3600) vs. Dirac Live (PC, stereo trial license), for speakers only (Philharmonic BMR). I did not include subwoofers in this comparison because Dirac from PC doesn't have direct access to the subs, so it wouldn't be a good comparison. I use MSO/miniDSP for subwoofer EQ anyway, so personally I'm not that interested in Dirac vs. Audyssey for that part. I also have a fairly well treated room (around 16x 2'x4' mineral wool bass traps/panels and various diffusers), so the amount of room correction the software needs to do is probably less than most rooms.
Method
Dirac Live was calibrated with a UMIK-1 using the tight focusing (9 point) mic pattern; the "measurement cube" length was around 2 ft. Audyssey was setup using the same measurement points with the Audyssey mic (there will be variation in exact mic positioning though). For the target curve, I used a -1 dB/dec target for both Audyssey and Dirac (tilt used in MultEQ-X, and the control points were adjusted in Dirac to match). MRC/DEQ is off in Audyssey. 30 Hz cutoff frequency was applied in Audyssey (around where the BMRs roll-off), with the Dirac target adjusted to achieve this. I did not put any additional bass boost.
Measurements
I did a 6 point measurement with REW at positions within the 9 point setup pattern (in about a 1.5 ft "bubble"), essentially around where my head would go. For each position, I measured Audyssey/Dirac/Uncorrected before moving to the next position. Var smoothing was used in REW, which doesn't smoothen the bass but smoothens the mid/highs. Postprocessing was done using Matlab to do the averaging/analysis/plot generation.
Feel free to recommend different ways or other ideas to analyze this data; a lot of you folks are much more experienced than me on this.
SPL vs. Frequency
Bass mode correction: Both Dirac and Audyssey do a similar job repairing room modes (below 500 Hz). Dirac is a few dB quieter than Audyssey by default.
Adherence to target curve: Dirac may be a little closer to the target curve, but keep in mind the mic I'm using for verification is the same mic used for calibration. Audyssey necessarily uses a different mic, so this is a clear inconsistency. Audyssey seems to boost the highs a little bit, and is more similar to the uncorrected response.
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Left/Right Speaker SPL Error vs. Frequency
The better the left and right speakers are matched, the better the imaging (correct me if I'm wrong on this assumption!). Below are plots comparing the left and right speaker response, averaged over the 6 measurement points. I also computed the error between right and left speakers.
Both Audyssey and Dirac do a good job at reducing the Left/Right mismatch, about halving the maximum error. Audyssey appears to be slightly better, but this may be within the noise.
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Left/Right Phase Error
Dirac is advertised as improving speaker phase, so I thought a measurement like this could capture it. As I understand, humans cannot hear absolute phase, but relative phase is detectable; reducing phase mismatch between the left and right speakers can improve imaging. In the below plot, the absolute value of the left/right phase error (averaged across 6 positions) is presented, as well as the average error as a single metric for comparison.
Both Audyssey and Dirac reduce the L/R phase error, but interestingly, Audyssey appears to be doing slightly a better job. Dirac looks to be doing something strange in the mid frequencies. Not sure what else to make of this.
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Subjective Impressions
Very briefly - I am finding that the Dirac response sounds a bit flat, and I prefer it off for the mid/high response. Audyssey sounds better on than off full range. This is probably due to the difference of the target curves, with Audyssey resembling the natural response of my BMRs more, which naturally has elevated highs (see
Erin's measurements). The extra boost in the upper freqs for Audyssey actually sounds nice to me, adding a bit of "sparkle" and soundstage. My hearing isn't that great up there so this helps. Bass sounds improved for both correction schemes.
My next plan is to change the Dirac target curve to be more similar to the Audyssey response (making it a more fair comparison), and try some blind tests with my wife as the subject.