Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 783 - AVS Forum | Home Theater Discussions And Reviews
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post #23461 of 23464 Old Today, 02:22 PM
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Originally Posted by lonestarwings View Post
In the first 2 charts above - take 6khz. The mic calibration file for my Umik-1 at 6002.27 hz is +2.43 db.

On the ALL SPL the 6khz ALL SPL on the right (red) channel is 92.67 db. On the Distortion Fundamental plot, it is 95.10 at 6 khz, for a difference of 2.43.

Similairly, at 24.62hz, the All SPL on the right channl is 89.50. On the distortion fundamental it's 90.25, a difference of 0.75, and the cal file is +0.75 at 24.62hz. So it appears that the response on the distortion fundamental graph is being corrected by the values in the cal file while the ALL SPL window isn.t

I apologize if I'm misunderstanding something. Also, someone on another forum told me that the "SPL & Phase" and "All SPL" windows don't include the mic cal files, which is what alerted me to it initially.
From the REW help file on the Distortion Graph:

"The plots of the Fundamental (the linear part of the measurement) and the distortion harmonics do not include mic/meter or soundcard calibration corrections. This is to avoid the effect of the corrections generating a misleading view of distortion levels. For example, mic/meter and soundcard calibration corrections boost the lowest frequencies of measurements to counter the roll-off of the mic/meter and soundcard interfaces, but adding those corrections to a distortion plot would make distortion appear to rise at low frequencies, hence their omission"
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post #23462 of 23464 Old Today, 03:57 PM
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Originally Posted by sam_adams View Post
From the REW help file on the Distortion Graph:

"The plots of the Fundamental (the linear part of the measurement) and the distortion harmonics do not include mic/meter or soundcard calibration corrections. This is to avoid the effect of the corrections generating a misleading view of distortion levels. For example, mic/meter and soundcard calibration corrections boost the lowest frequencies of measurements to counter the roll-off of the mic/meter and soundcard interfaces, but adding those corrections to a distortion plot would make distortion appear to rise at low frequencies, hence their omission"
Ok, so I guess I was misunderstanding the meaning of the +/- values of the calibration file. I guess a - would mean the mic reads low at that frequency and the corrective value needs to be added to the raw measurement, and a positive number means it reads high and the corrective value needs to be subtracted. Thanks for clarifying that for me!
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post #23463 of 23464 Old Today, 04:39 PM
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Originally Posted by AustinJerry View Post
Well, the "All SPL" is a display window that shows existing measurements. When the measurements were originally taken, they were taken with the mic cal file in effect. Simply displaying a pre-existing measurement in the All SPL window doesn't remove the cal file adjustments. That would be weird, wouldn't it?

Using the UMIK-1 and REW to measure headphone output is somewhat unusual, and I don't claim to have ever tried it, or understand how it could be done.. Not sure whether the measurements you are getting are accurately capturing the frequency response of your headphones, which are very nice indeed.
Yeah, I definitely loaded the calibration file in beforehand. I was just misinterpreting the postive/negative values of the .cal file and operating on some questionable advice.

Here is the measurement rig. The coupling surface is creatology foam with graduation marks for placement repeatability, foam blocks for structure, and some polyfill on the surface immediately around the mic. A lot of people on superbestaudiofriends.org do this kind of thing and a few on head-fi.







It's not as far off from some pro measurements as I though it'd be. It seems pretty accurate until about 7 khz or so, compared to this pro measurement from Innerfidelity:
On my rig:


Same Headphone make/model pro measurement:
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post #23464 of 23464 Old Today, 05:20 PM
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The reviews on your headphones are stellar. Very nice! I guess you must be a headphone kind of guy. That measurement rig is pretty creative.
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