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DIY Digital Room Correction with Linux

by pcr910303 on 10/2/22, 6:35 AM with 24 comments

• by scarecrowbob on 10/5/22, 7:59 PM

  It's fun stuff to mess with, but one difficulty is that you can't really affect time-domain issues by modifying output frequencies.

  That is, there are likely both issues induced by the phase response of the speakers themselves as well as issues introduced by reflections in the room which will cause uneven frequency responses in these measurements. These issues are inherent in speaker systems and acoustic spaces.

  If you have a really resonant frequency in a room, notching that frequency can help, but then you're compromising that signal; a more typical solution is to address reflectivity in the space.

  And I hate to be a snob about mics, but yee, I do not like that specific mic-- of the many dozens of mics I have used it's memorably bad. And you don't need an expensive mic to do these measurements; there are a lot of ~$60 omni-directional measurement mics that work fine, as their low/mid frequency response is good enough for these tasks.

  So all in all: hooray for folks experimenting... once you start playing with frequency modification, start investigating phase response and modal reflections in rooms, as they are super interesting.

  Like, if you want to hear something really neat, put on a recording of a 120hz sine in a very reflective room, and you can walk around and hear the nulls and additions. And then you can find different frequencies and start to come to terms with the complexity there. Quite a fun exercise.

• by JohnBooty on 10/5/22, 7:42 PM

  It cannot be understated how much better even modest/mediocre speakers can sound when their in-room response is corrected via DSP.

  (This is essentially why a lot of consumer electronics sound surprisingly good these days: onboard DSP is cheap and easy to implement. What a blessing!)

  Conversely, even "high end" speakers can sound bad if not dialed in correctly, especially if your room is rectangular and there are a lot of reflections.

• by bob1029 on 10/5/22, 7:34 PM

  I used to run an outboard FIR filter for my subwoofer with weights calculated (in part) using REW. I can't recall the actual DSP hardware model, but it was a pretty amazing effect when you toggled it on/off.

  Today, I just have a miniDSP that does basic crossover duty. I haven't bothered to do any parametric EQ or more advanced filtering in my new office yet. The passive acoustic treatments have done such wonders that I probably can't be now.

  I don't really like running anything above 80Hz through digital filters that I have constructed myself. I've had some success in a few areas, but you can instantly tell something isn't quite right with certain content.

• by yamtaddle on 10/5/22, 7:42 PM

  The biggest problem with home theater setups with surround sound, IME, is that no matter what you do most of the seats will get very uneven sound (typically, one or more surround speakers being much louder than the others). The only fix is to have a larger space so the effective "sweet spot" covers more of your seating (think: an large-aisle-width space around a 3x2 seat configuration) but at that point you're looking at sacrificing a mid-sized living room worth of square footage for those 6 total viewing seats (and even more, if you scale up from there).

  [EDIT] In case it's not clear, the core problem is that for some seats, without a large buffer between the seating area and the speakers, the nearest surround speaker will be like 5-10% as far away as the farthest one. No amount of room-correction can help much for most of the seats in such an arrangement. All you can do is use a larger space so you can put the speakers farther away without changing the size of the seating area (so, add empty buffer space around the seating area) so the difference in relative distance between the farthest and nearest surround speakers is smaller.

• by eating555 on 10/5/22, 7:06 PM

  Good to see the detailed write-up! Many others are just a brief guide to make you buy their service or product.

• by m463 on 10/5/22, 8:33 PM

  > That seems like a reasonable thing to do, but there is a lot of pseudoscience in the audio world that will get you to buy platinum tipped styluses for depressing buttons on your remote.

  I think there are a LOT of these. I wish I knew when "reasonable" or "plausible" pan out.

• by sillystuff on 10/5/22, 11:38 PM

  > often had to have the volume at a bare minimum of 50% in order to hear speech correctly. Now I could get away with 15%.

  Sounds like you don't need a mic or anything other than the EQ to make movies watchable. Just reduce every frequency range other than that of human voices. No more having your ears blasted by loud music / explosions because, earlier, you had to turn the volume up to maximum in order to barely hear the dialog.

• by dt2m on 10/6/22, 6:32 AM

  I recently bought a "t.racks DSP 4x4 Mini" which is an inexpensive hardware DSP box capable of the same. I just have it sitting between my soundcard and some active speakers.

  Gives me peace of mind knowing my EQ curve always is on even if I'm using software that's outputting direct to my interface.

• by edude03 on 10/5/22, 7:28 PM

  I've been interested in this topic recently, I hate my AVR, but there isn't a better alternative. I've been hoping instead of an AVR I could pipe HDMI into my PC and run DIRAC there, but I've yet to find a capture card that can capture DTS/Atmos etc, so it hasn't been fruitful

• by natdempk on 10/6/22, 1:07 PM

  Does anyone know how this compares to something like Sonarworks, which does a similar process but for a series of measurements across your room with a specific microphone they provide?