5 ms·

DIY Digital Room Correction with Linux

91 points by pcr910303 4y ago

eating555 4y ago
Good to see the detailed write-up! Many others are just a brief guide to make you buy their service or product.
edude03 4y ago
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
- brokenmachine 4y ago
  Check out minidsp stuff.
bob1029 4y ago
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.
- MartijnBraam 4y ago
  I too did this exact thing with hardware instead of doing it in Linux. I used an t.racks DSP 4x4 Mini to apply my REW-measured room correction between my sound card and amp, also use it to generate the split for my subwoofer.
- montag 4y ago
  How do you like the miniDSP? Thinking about getting one - room correction definitely seems like a job for hardware; i.e. easy enough for a DSP, more portable and hassle-free than setting up software on one computer.
  - bob1029 4y ago
    It's pretty good. I have the 2x4HD and no complaints. The software is adobe air crap but it works well enough. I am using it as a USB DAC driving a pair of stereo monitors and 2x subwoofers at the moment.
yamtaddle 4y ago
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.
- toast0 4y ago
  I'm in the middle of a dedicated theater room project. We're doing 5 seats behind 4 seats, which is probably more than we'll likely use, but it does have the benefit of expected use will have people farther away from the side speakers. Depending on the seating costs and budget and other things, I think it makes sense to go ahead and put seats around the sides... in case you end up having extra guests, they can sit in comfort, even if the audio isn't ideal. On a small budget, you can do a lot with just two decent speakers rather than speakers built into an ultra thin flat panel. Thrift stores often have nice speakers that may not be visually pleasing but are likely to be aurally pleasing.
  - yamtaddle 4y ago
    > On a small budget, you can do a lot with just two decent speakers rather than speakers built into an ultra thin flat panel. Thrift stores often have nice speakers that may not be visually pleasing but are likely to be aurally pleasing. This is very true, almost any separate speaker is going to be better than TV speakers, especially in the age of flat panels. And one thing software room-compensation can do is let you build a surround system with mismatched speakers, without having to lose a day manually tweaking levels. No need to buy a full 7.1 or 7.2 set at once. Thrift decent pairs of speakers and orphaned subwoofers and let the software figure it out.
JohnBooty 4y ago
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.
scarecrowbob 4y ago
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.
- m463 4y ago
  > And I hate to be a snob about mics I wonder if you just need a mic with a calibration file? this one is less than $25: https://smile.amazon.com/dp/B00ADR2B84 https://smile.amazon.com/dp/B00ADR2B84 and you can use the serial number to download a specific calibration file
  - scarecrowbob 4y ago
    I have a Dayton Audio EMM-6 that I own and had in mind. It's not Earthworks, but it's good nuff and I like an XLR out for my purposes.
  - atoav 4y ago
    In the end a mic is just a converter of air movement to electricity fluctuations. The hard part in measurement mics is that they don't show any characteristic that deviates from the expectation both in the time and frequency domain. Calibration files can help you in the frequency domain (provided that mic is stable over it's lifetime), but the time domain is a different beast as in: if we play a square click how well can the mic reproduce the square and/or what kind of artifacts are added by it. In the end the question is, how important calibration is for your purpose. If you are a hobbyist, I would even say, you don't really need it more than once. If you mix/master productions that have high budgets maybe spending a little bit more on making sure everything works makes more sense. If you are the hobbyist, maybe renting is a good option?
m463 4y ago
> 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.
- tuatoru 4y ago
  Room EQ Wizard is your friend.
sillystuff 4y ago
> 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.
dt2m 4y ago
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.
natdempk 4y ago
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?

91 points by pcr910303 4y ago

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

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

brokenmachine 4y ago
Check out minidsp stuff.

bob1029 4y ago

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.

MartijnBraam 4y ago
I too did this exact thing with hardware instead of doing it in Linux. I used an t.racks DSP 4x4 Mini to apply my REW-measured room correction between my sound card and amp, also use it to generate the split for my subwoofer.
montag 4y ago
How do you like the miniDSP? Thinking about getting one - room correction definitely seems like a job for hardware; i.e. easy enough for a DSP, more portable and hassle-free than setting up software on one computer.
- bob1029 4y ago
  It's pretty good. I have the 2x4HD and no complaints. The software is adobe air crap but it works well enough. I am using it as a USB DAC driving a pair of stereo monitors and 2x subwoofers at the moment.

yamtaddle 4y ago

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.

toast0 4y ago
I'm in the middle of a dedicated theater room project. We're doing 5 seats behind 4 seats, which is probably more than we'll likely use, but it does have the benefit of expected use will have people farther away from the side speakers. Depending on the seating costs and budget and other things, I think it makes sense to go ahead and put seats around the sides... in case you end up having extra guests, they can sit in comfort, even if the audio isn't ideal. On a small budget, you can do a lot with just two decent speakers rather than speakers built into an ultra thin flat panel. Thrift stores often have nice speakers that may not be visually pleasing but are likely to be aurally pleasing.
- yamtaddle 4y ago
  > On a small budget, you can do a lot with just two decent speakers rather than speakers built into an ultra thin flat panel. Thrift stores often have nice speakers that may not be visually pleasing but are likely to be aurally pleasing. This is very true, almost any separate speaker is going to be better than TV speakers, especially in the age of flat panels. And one thing software room-compensation can do is let you build a surround system with mismatched speakers, without having to lose a day manually tweaking levels. No need to buy a full 7.1 or 7.2 set at once. Thrift decent pairs of speakers and orphaned subwoofers and let the software figure it out.

JohnBooty 4y ago

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.

scarecrowbob 4y ago

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.

m463 4y ago
> And I hate to be a snob about mics I wonder if you just need a mic with a calibration file? this one is less than $25: https://smile.amazon.com/dp/B00ADR2B84 https://smile.amazon.com/dp/B00ADR2B84 and you can use the serial number to download a specific calibration file
- scarecrowbob 4y ago
  I have a Dayton Audio EMM-6 that I own and had in mind. It's not Earthworks, but it's good nuff and I like an XLR out for my purposes.
- atoav 4y ago
  In the end a mic is just a converter of air movement to electricity fluctuations. The hard part in measurement mics is that they don't show any characteristic that deviates from the expectation both in the time and frequency domain. Calibration files can help you in the frequency domain (provided that mic is stable over it's lifetime), but the time domain is a different beast as in: if we play a square click how well can the mic reproduce the square and/or what kind of artifacts are added by it. In the end the question is, how important calibration is for your purpose. If you are a hobbyist, I would even say, you don't really need it more than once. If you mix/master productions that have high budgets maybe spending a little bit more on making sure everything works makes more sense. If you are the hobbyist, maybe renting is a good option?

m463 4y ago

> 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.

tuatoru 4y ago
Room EQ Wizard is your friend.

sillystuff 4y ago

> 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.

dt2m 4y ago

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.

natdempk 4y ago

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?