Addicted to Fun and Learning
- Sep 22, 2021
- Albuquerque, NM USA
Interesting. I think your explanation has helped me gain a deeper appreciation of the problem. For one, it leaves me thinking that there is much to recommend high DI speakers away from the walls with separate ambience channels.Nothing in Room Correction software is quite as complicated as that. Dirac is different in this regard as the multiple measurements are separate and information from each measurement can be processed separately, they do have some papers I have read before describing parts of it.
These are the steps performed by DRC_FIR
Frequency dependent windowing is the main function that assists with separating the speaker from the room. In REW the window is quite basic and is in cycles or octaves for the whole range. This still means that the window is short at the top and long at the bottom.
- Initial windowing and normalization of the input impulse response.
- Optional microphone compensation.
- Initial dip limiting to prevent numerical instabilities during homomorphic deconvolution.
- Decomposition into minimum phase and excess phase components using homomorphic deconvolution.
- Prefiltering of the minimum phase component with frequency dependent windowing.
- Frequency response dip limiting of the minimum phase component to prevent numerical instabilities during the inversion step.
- Prefiltering of the excess phase component with frequency dependent windowing.
- Normalization and convolution of the pre-processed minimum phase and excess phase components (optional starting from version 2.0.0).
- Impulse response inversion through least square techniques or fast deconvolution.
- Optional computation of a psychoacoustic target response based on the magnitude response envelope of the corrected impulse response.
- Frequency response peak limiting to prevent speaker and amplification overload.
- Ringing truncation with frequency dependent windowing to remove any unwanted excessive ringing caused by the inversion stage and the peak limiting stage.
- Postfiltering to remove uncorrectable (subsonic and ultrasonic) bands and to provide the final target frequency response.
- Optional generation of a minimum phase version of the correction filter.
- Final optional test convolution of the correction filter with the input impulse response.
So you get progressively more room in the measurement as frequency goes down.
DRC_FIR goes further with a sliding window where the length of the window can be set different at both the low frequency and high frequency independently and there is also an exponent parameter to change how the two interact in the middle. Changing the window exponent is one factor that has a big impact on the way the correction sounds. Differences of 0.01 are audible as it strongly affects the midrange.
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This really lets you tailor just how much speaker correction vs room correction is being done. I see very few speakers where the direct sound still couldn't be smoother but whether messing with this has a positive effect depends a lot on how even the directivity of the speaker being corrected is.
I just wonder how well the Apple Music Atmos remastered titles will sound. Personally, the films I enjoy the most don't depend a lit on gee whiz sound effects. It's not that I don't enjoy the enhanced realism. Just been never enough of a draw to invest tge time and equipment into a multichannel set up. One of those two channel purists (or Luddites depending on ones perspective) I guess, as done fight, there is great satisfaction to be had.
Of course Toole and others hzvd been saying this for a long time. Always been a matter of software, and perhaps we are at the dawn of a new era when there is a plethora of music in MCh formats, and having 4 or 5 really good speakers will be far more important than having two gobsmackers, cable lifters, along with Shaman and quantum mechanics to get everything just so.
I really want to thank you for breaking down the DRC flow for me. That exponential windowing sensitivity reminds me a bit of tinkering with gamma in photoshop type software. I can imagine it doesn't take much tinkering to ruin an otherwise good image. Gonna have to mull all of this over a bit.