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Room Measurement Tutorial for Dummies Part 2

Dennis_FL

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Hi Dennis,
I don't have Roon, or indeed know anything about it. Any particular reason for exploring this program? I generally stream from iTunes from a laptop, if that matters...
Roon is organizing software for your digital library and can also link with Tidal and/or Qobuz. It is similar to JRiver and JRiver can also do digital room adjustments.

If you do room correction upstream of the DAC) Roon can take the output file of REW and do the adjustments with a filter

Digital tunes -- > Roon room correction --- > DAC --->Pre Amp (link here for help)

If you do adjustments downstream of the DAC (like with Audyssey in an AVR receiver or a miniDSP) then the analog signal from the DAC needs to be converted back to digital and then after room corrections, back to analog

Digital tunes --> DAC --> ADC ---> Room Correction-->DAC---> Pre Amp (link here )

or if you don't have a DAC.....you can use REW in a miniDSP with digital inputs

Digital tunes --> miniDSP---> Room Correction-->miniDSP DAC---> Pre Amp
 
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luft262

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This is from 2016! Is there a part 3 out there?
 

Pugsly

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This is from 2016! Is there a part 3 out there?
Sadly, no. I received a umik for Christmas, and then discovered that like other audio forums, @amirm is also full of false promises and broken dreams :eek:. In all seriousness, I would love to see part 3... Hope your water woes are solved!
 

luft262

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Sadly, no. I received a umik for Christmas, and then discovered that like other audio forums, @amirm is also full of false promises and broken dreams :eek:. In all seriousness, I would love to see part 3... Hope your water woes are solved!
I would love a 3rd part as well, but trust me that Amir is a treasure trove of information and with just a little digging you'll be glad to have found Audio Science Review.
 

djigibao

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Check this out....

 

nhs

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What happened to REW Part 3?
Part 3?, no I'm going back to part 1.;)
I've been experimenting with the free DRC-FIR room correction software for a couple months now. If you feed it an impulse response exported from REW, it produces a correction filter (FIR filter) that can be used with a convolution engine. I use the free brutefir convolution engine with the BrutefirDRC plugin for Logitech Media Server.

Archimago had an excellent post on BrutefirDRC a few years ago.

For the speaker+room frequency response, I use REW and a UMIK-1 mic. I generate the left/right measurement sweep files from the REW Generator dialog and then copy them to my music server to play them back through my system later (click to embiggen).

View attachment 24256

For playing "offline" like this, make sure you check "Add Timing Ref". This adds a short chirp before the sweep proper starts. You would then check "Use acoustic timing reference" in the "Measure" dialog so that it will wait for this chirp to start recording.

View attachment 24258

Click "Start" to start the measurement and then play back the sweep from the music server. Once you have a measurement, export it to a 32-bit WAV file: File -> Export -> Export Impulse Response as WAV.

View attachment 24259

DRC-FIR needs the impulse response in a "raw" format as 32-bit floating point numbers. I use sox to convert from WAV to the raw format:

$ sox impulse.wav -t f32 impulse-44100.pcm rate -v -s 44100

Here I've converted the WAV file to raw bytes and downsampled it to 44100.

I do all my processing on a Linux Mint box, and there it's very easy to install DRC-FIR

$ sudo apt install drc

But binaries are also provided for Windows in a tarball (they are in the sample directory).

DRC-FIR has a ton of adjustable parameters that affect how the correction is computed, but it also provides a set of standard configuration files with preset parameters with different levels of correction. These are named: minimal, erb, soft, normal, strong, extreme, and insane. These config files are provided for 44.1, 48, 88.2 and 96 kHz sample rates.

So finally, to turn the measured impulse response into a correction filter, the drc command is

$ drc --BCInFile=impulse-44100.pcm --PSOutFile=filter-l-44100.pcm --MCPointsFile=7032857.txt "/usr/share/drc/config/44.1 kHz/normal-44.1.drc"

Breaking it down: BCInFile is our input impulse response measurement, PSOutFIle is where the correction filter will be saved, MCPointsFile is the microphone frequency response correction file (You can just leave this empty if you don't have a correction file) and the final file name on the line is the DRC-FIR config file with the parameters that will be used. By default, drc uses a "psychoacoustic" target file, but several target files, such as the popular B&K target, are also provided, or you could make your own target file (it's just frequency/amplitude pairs).

Of course, I don't type all those commands in, I have a shell script that automates everything. Maybe more on that later, but on to some graphs...

Here are before and after plots of frequency response with 1/6 octave smoothing using the "normal settings".

View attachment 24265
View attachment 24266

I haven't quite figured out how to interpret some of the other plots that REW provides yet.

The gear chain is

Logitech Media Server ==> RPi-3B running piCorePlayer ==> Auralic Vega USB ==XLR==> Bryston 3B-SST ==> Vandersteen Quatros

The Quatros have built in active subwoofers with an 11-band analog EQ, which I've set to flat for this measurement and test.

So how does it sound? Well for the past month I've been really enjoying it with a different gear chain with a tube preamp and tube monoblocks, and there DRC-FIR did a wonderful job of cleaning up the bass and tightening up the imaging. I would never want to go back to un-corrected.

However with this alternate "purist" chain the bass seems a bit too light and the treble is a bit too tipped up. You can see a rise in the treble of the corrected response starting at about 6 kHz. TIme to experiment with some different settings and target files.
I have done following steps:
  1. Measured 48 kHz impluse responses using REW and UMIK1.
  2. Exported the mono IR to 32 bit float wav file ImpluseResponse48k-f32.wav.
  3. Resampled and converted the IR to raw PCM file for Denis Sbragions DRC using SoX.
    • sox ImpluseResponse48k-f32.wav -t f32 -r 96k ImpluseResponse96k-f32.pcm
  4. Made convolution filters left/right .pcm using DRC.
  5. Converted left/right .pcm filters to stereo .wav filters convolved by CamillaDSP running on RPI4.
It sounds very well on my equipments. Now, I like to remeasure the before/after impulse responses with REW like many have done here. But I don't have any plan how to do that. Is it possible to do that if my HiFi chain only looks like below?
Synology NAS (Minimserver) --> RPI4 (Moode, CamilllaDSP, UpnP) --> USB-Cable --> Topping D90SE --> Speaker-Amp --> Speakers

One other question, did some one make DRC config files for 176.4 kHz and 192 kHz sample rates?

Thank you for any hints.
 
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Daverz

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Part 3?, no I'm going back to part 1.;)

I have done following steps:
  1. Measured 48 kHz impluse responses using REW and UMIK1.
  2. Exported the mono IR to 32 bit float wav file ImpluseResponse48k-f32.wav.
  3. Resampled and converted the IR to raw PCM file for Denis Sbragions DRC using SoX.
    • sox ImpluseResponse48k-f32.wav -t f32 -r 96k ImpluseResponse96k-f32.pcm
  4. Made convolution filters left/right .pcm using DRC.
  5. Converted left/right .pcm filters to stereo .wav filters convolved by CamillaDSP running on RPI4.
It sounds very well on my equipments. Now, I like to remeasure the before/after impulse responses with REW like many have done here. But I don't have any plan how to do that. Is it possible to do that if my HiFi chain only looks like below?
Synology NAS (Minimserver) --> RPI4 (Moode, CamilllaDSP, UpnP) --> USB-Cable --> Topping D90SE --> Speaker-Amp --> Speakers

One other question, did some one make DRC config files for 176.4 kHz and 192 kHz sample rates?

Thank you for any hints.

Yes, use the REW Generator tool to generate a measurement sweep file with timing reference (the timing reference should be on the same channel for both left and right, say left). Save as a 48k/24-bit wav (Logitech Media Server can't handle 32-bit float files, YMMV). I usually convert it to a FLAC and tag it for playback from my music server. Then when doing a measurement, make sure computer speaker is off, select "timing reference" when doing your measurement, click "Start" and then play the sweep from the server. You may have to adjust the volume before REW "hears" the timing reference chirp.

Compare with a test convolution computed by DRC-FIR. You may find that the test convolution is a good enough approximation of the measurement.
 
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nhs

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Yes, use the REW Generator tool to generate a measurement sweep file with timing reference (the timing reference should be on the same channel for both left and right, say left). Save as a 48k/24-bit wav (Logitech Media Server can't handle 32-bit float files, YMMV). I usually convert it to a FLAC and tag it for playback from my music server. Then when doing a measurement, make sure computer speaker is off, select "timing reference" when doing your measurement, click "Start" and then play the sweep from the server. You may have to adjust the volume before REW "hears" the timing reference chirp.

Compare with a test convolution computed by DRC-FIR. You may find that the test convolution is a good enough approximation of the measurement.
Thank you @Daverz , I never realize the Generator tool REW has. I'll try it when I'm at home.
A very important thing you said "the timing reference should be on the same channel". As I remembered at last measurement, I used the acoustic timing reference on different channel. So I have to correct it for next measurements.
Some further questions are risen now.
1) Is the timing reference relevant for exporting the IR to DRC-FIR?
2) Should the check box "Normalize sample to peak value" be checked for exporting IR to DRC-FIR?
3) Should the check box "Apply IR window before export" be checked for exporting IR to DRC-FIR?

Thank you very much!
 
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Daverz

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Thank you @Daverz , I never realize the Generator tool REW has. I'll try it when I'm at home.
A very important thing you said "the timing reference should be on the same channel". As I remembered at last measurement, I used the acoustic timing reference on different channel. So I have to correct it for next measurements.
Some further questions are risen now.
1) Is the timing reference relevant for exporting the IR to DRC-FIR?
2) Should the check box "Normalize sample to peak value" be checked for exporting IR to DRC-FIR?
3) Should the check box "Apply IR window before export" be checked for exporting IR to DRC-FIR?

Thank you very much!

The timing chirp is only used when REW computes the impulse response, so it's not relevant to export. It's needed to compensate for clock drift when playing back the measurement sweep from the music server. You want it on the same channel (can't remember who here pointed this out to me), so you have the same reference for both channels.

You want to export as 32-bit float, so I don't think any dynamic range is lost by not normalizing, and that will just cause clipping if you need to resample the impulse response. I've never used "Apply IR window".
 
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Mehdiem

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Hey guys, I’m planning to buy an UMIK1, I was wondering if you any perspective/experience comparing the Cross Spectrum Labs, Calibrated UMIK1 mics, which cost about $35CAD in my case, against non-calibrated ones?
 

nhs

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Hi all,
I have to get rid of a question about the target curve for DRC-FIR. Searching the internet I only found 0.0 db is maximal value for the target curve. The question is why?
What is wrong if I lift the values to +3db for the frequency range from 100 - 120 Hz?
 

Mehdiem

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I have performed my first measurement with UMIK-1 and REW. I need your help to understand how to generate & translate my EQ measurements into RME parameters.

I could not find a way to generate EQ according to RME parameters and capabilities. I tried using Generic EQ with 7 filters but didn't work out well. Please note that: RME has 5 EQ + 2 (Bass/Treble)

- Please see my measurement as attached
- I measured with sub-on crossover 60hz
- I use a custom Herman house curve, that I found online as follows:
  • 31.5 6​
  • 40 5.9​
  • 50 5.5​
  • 63 4.9​
  • 80 3.7​
  • 100 2.5​
  • 125 1.3​
  • 160 0.6​
  • 200 0.2​
  • 250 0​
  • 1000 -1​
  • 32000 -6​

Please let me know if there is any recommended setting for generating EQ.
Screen Shot 2022-02-23 at 2.28.00 PM.png
Screen Shot 2022-02-21 at 4.08.13 PM.png
 

Jim Shaw

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Amir did not. Studios did not pay him for the third installment of the movie so it is not getting shot yet. :D

One of these days I will get around to it. :)
Did Part 3 ever happen? I'm weary of looking everywhere for it...

"Part 3, part 3, where art thou part 3?
 

Jim Shaw

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Sorry…no part 3
Ah, so here I go, alone... all Tristan and no Isolde... measuring my room with no calibration of me. <sigh>
 
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