Re: Measurements before and after Digital Room Correction
Someone was asking about distortion (much) earlier and received different answers.
Experiment:
Setup:
PC REW -> USB -> Topping D10 -> Optical -> Audio authority 1177A switch -> Coaxial -> Focusrite Clarett 4Pre USB -> Focusrite Internal Matrix -> Focusrite Monitor Output 1 -> Focusrite Internal Matrix -> USB -> PC REW
First stream passes through all the gear above, but no filters are applied.
Second stream has some old AcourateDRC filter applied at the miniDSP OpenDRC-DI, a single point measurement was used to create the filter, for MartinLogan reQuest speakers in this room, with an "aggressive" full range filter. Both FIR and IIR filters are part of the correction.
Measurement is of the left channel digital stream as received by REW.
-6db is applied to both streams at the miniDSP OpenDRC-DI.
Conclusion:
To say there is "no distortion" added to the digital signal with digital room correction is false in this case
However, I would consider the increase in distortion at the digital signal level as measured here to inconsequential.
Frequency Response:
Green - no "correction"
Violet - "corrected"
Phase adjustments
Distortion as THD
Harmonics:
No correction:
(noise floor is the upper brown trace)
With correction: