Differences

This shows you the differences between two versions of the page.

--- audio:rew:rew [2025/12/21 12:03] – [Multiple Averaged Measurements] oscar
+++ audio:rew:rew [2025/12/22 09:11] (current) – oscar
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 ====== Room EQ Wizzard ======
+----
 REW will be used to do the following:
   - Measure the room frequency response;
   - Generate create the initial parametric EQ filter settings to achieve a flat frequency response.
-For each individual stereo channel do the following steps:
-==== UMIK-1 setup ====
-With the miniDSP UMIK-1, you have an easy way to get a precise acoustic measurement. First download the calibration file for your microphone. Each microphone has a unique calibration file, which define the specific frequency characteristics of each individual microphone. The calibration file ensures that your microphone is as accurate as possible. Go to the UMIK-1 page and enter your microphone's serial number. It is in the form xxx-yyyy and labeled on the microphone. There are 2 versions of of the calibration files available. One version for the microphone directly aimed at the speakers (stereo setup) and one 90 degree version for the microphone aimed at the ceiling (for surround sound setup). Use "Save As" in your browser to save the numbers as a file e.g. 7000343.txt.
-Connect the UMIK-1 to your computer using the supplied USB cable. Once installed, start REW. You will see a screen asking if you want to use the UMIK-1. Click on Yes. (If you don't get this screen, go to the REW Preferences window and set the Sample Rate to 48 kHz.)
-{{ :audio:rew-1.jpg?400 |}}
-=== UMIK-1 for phase measurements ===
-USB mics can be used with the acoustic timing reference feature. Turn on the "__Adjust clock with acoustic ref__" Analysis option to have REW try and compensate for the variations. This will be usefull for Phase measurements, that rely on accurate timing.
-==== Set levels ====
-The UMIK is automatically calibrated by REW for sound level (this information is in the calibration file). But you need to set your system to generate a suitable signal level. Click on the Signal Generator button and set the parameters like illustrated below. Position your microphone at the listening position and turn the volume of your system down. Then click on the Play button (green triangle), and turn the volume up until the test signal is at a comfortable level.
-{{ :audio:rew-2.jpg?400 |}}
-Now open the REW SPL Meter. Click on the red button in the lower right corner to turn it on, and adjust your system volume until the meter reads about 75 dB.
-{{ :audio:rew-3.jpg?400 |}}
-==== Run a measurement sweep ====
-Click on the Measure button near the top left of the main REW Screen. Check that the level is set to -12 dB, the output and input channels are properly set and finally click on the Start Measuring button.
-{{ :audio:rew-4.jpg?400 |}}
-REW will make a "whoo-oop" sound through your speakers. A short time later, you should see your first in-room measurement and present the measured frequency response in the window.
-{{ :audio:rew-5.jpg?400 |}}
-==== Smoothing ====
-Using REW filters generation and calculate the amplitude correction. As the averaged measurement contains all the information from the individual measurements, you can decide to smooth the curve, using FDW or smoothing tools from REW, in order to generate the filters. The smoother the curve you use  to calculate the correction, the less filters will be generated by REW.
-Additional smoothing is not needed if FDW (frequency dependent windowing) has been enabled. But if you do, use VAR smoothing as this will wisely smooth differently across the frequency spectrum and will require less EQ in higher frequencies.
-Depending on the measurement I use 1/12th or 1/24th octave smoothing and 15 cycles FDW to generate the correction filters and avoid ‘micro-managing’ the amplitude and phase corrections.
-But before averaging, you need to check whether you have selected a default FDW in your preferences of REW. If so, you need to be aware that the algebraic functions will be conducted with this FDW applied at each step. This is not a problem, but you should be aware of this. We will use No FDW.
-{{ :audio:REW-average-1.jpg?400 |}}
-==== Multiple Averaged Measurements ====
-=== Measuring ===
-In REW it is possible to average a number of measurements. The idea behind this is to eliminate over-corrections which validity is limited to the exact place where the microphone has been setup in case of a single measurement. Use an imaginary cube of 25 cm around your hear position and perform +/- 5 measurements all at ear height with the mic always pointing to the front wall (or to the ceiling if your mic
-is designed that way and it has 90 degrees calibration file). Resulting in a total of 10 measurements for
-two speakers - to the left, right, front and rear of the LP each around 25 cm away from LP. If you
-consider bass upper frequency limit to be 200 Hz which converts to a wavelength of 43 cm, a 50 cm
-wide (25 x 2) measurement area seems to cover enough of the bass waves.
-For the center head position, take two measurements for Left and Right speakers as this is
-the most important location. Using two measurements at the LP will give a slight bias to the central position during averaging. Keep both measurements if they are identical (they should be
-identical at least past the speaker’s lowest bass frequency capacity). If they are not identical it is
-probably caused by some unwanted environmental noise during measurement, you should delete
-the irrelevant looking one.
-=== Time Alignment ===
-Before averaging make sure that all measurements are time aligned prior to making any kind of algebra on these measurements. Select the corresponding measurements inside the ‘All SPL’ tag of REW and use the ‘Time Align’ function in the Control window.
-__Do not align IR starts!__
-=== Averaging ===
-Select the measurements you want to average in the ‘All SPL’ tag of REW and use an Average function inside the Control window.There are several algorithms for averaging. __Vector Average__ differs from other methods (like RMS Average) because it sums magnitudes and phases coherently, meaning phase differences cause cancellation and dips, especially in high frequencies or different positions, which is great for multiple measurements at the same spot but less so for different locations. The __RMS Average__, however, treats measurements as incoherent (ignores phase) by averaging power, resulting in a smoother curve without deep nulls from phase cancellation, making it better for multi-position averaging (like across a listening area). The difference often appears as dips in the vector average that aren't in the RMS average, due to reflections or timing variations between measurements.
-When to Use Which Average
-  * Vector Average: Use for multiple measurements from the exact same spot (or time/level aligned) to see the coherent sum, good for detailed analysis and filter generation for that specific point.
-  * RMS + Phase Average / dB + Phase Average: Good for multiple measurements from different spots, averaging power while keeping phase info, resulting in a smoother, less cancelled curve.
-  * RMS Average: Best for averaging many measurements from different locations (spatial averaging) to get a general, smooth representation of the overall room response, effectively removing reflections.
-  *
-Why They Differ (The "Problem")
-  * Phase Cancellation: With vector averaging, if measurements have slight timing shifts (due to reflections, mic placement differences, or clock drift), the phase relationship changes, causing destructive interference (dips) at certain frequencies.
-  * Coherent vs. Incoherent: Vector averaging is coherent (like summing sound waves in phase), while RMS averaging is incoherent (like summing sound power), which doesn't cancel out.
-  * Spatial Averaging: For multiple listening positions, RMS averaging is better because it averages the power (what you hear) rather than the complex wave, which is less affected by reflections and phase.
-Solution if They Differ Unexpectedly
-  * Time-Align: If using Vector Average for nearby spots, time-align the impulse responses first using REW's tools.
-==== Save Measurements ====
-Now save the measurement so that it can be used in Rephase as a baseline measurement. Select "File -> Export Measurement -> Export Measurement as text".
-{{ :audio:rew-6.jpg?400 |}}
-==== Generate EQ filter ====
-Now we will create equalization filters for each channel using REW’s own EQ filters tool.
-Select the “Left Speaker Average” measurement and click the EQ button. In the popped-up EQ window, change
-smoothing to VAR (it should be at 1/48 smoothing by default due to FDW and you can even select
-“no smoothing” as vector average of various measurements is already smooth enough in most
-cases). VAR smoothing is good if you will EQ in the whole frequency spectrum and RePhase it later. If
-you will just EQ the bass frequencies just leave it as is.
-In the top menu press the EQ button and apply the following settings:
-  * On the right side of EQ window under Equaliser choose __rePhase__.
-  * Under Target settings configure a target type as close to your speakers’ true frequency response as possible. In my case "__Full Range Speaker__".
-  * House Curve: preferred settings for your room. Set target level to have REW set the target level or configure it manually.
-  * Target Level (dB SPL). Should be around the lowest dips of the frequency response to avoid the EQ from boosting too much. You can use the button "__Calculate level from Response__" which will suggest an appropriate level.
-  * The "__Allow narrow filters below 200 Hz__" option lets REW use very narrow filters (high Q) to correct peaks from room modes (standing waves) in the low bass region to tame bass peaks, while unchecking it (for device EQ) limits filters to a maximum Q of 5, preventing over-correction and distortion in the bass. It's generally selected for room correction (bass) and deselected for headphone/device EQ.
-  * Option "__Vary max Q above 200 Hz__" allows to use progressively narrower (higher Q) filters for bass issues below 200 Hz but allows for broader (lower Q) filters at higher frequencies, preventing overly sharp, unnatural-sounding corrections above the bass region, aiming for a smoother, more musical result as it moves toward treble. It's often used with "Allow narrow filters below 200 Hz" for comprehensive correction.
-{{ :audio:rew-7.jpg?400 |}}
-=== Generate ===
-Under Filter tasks hit "__Match response to target__". Hit EQ filters button to get dialog for additional manual filter adjustment.
-Check the deep dips for their wavelength with the simple formula: __distance (in metres) = 85.75 / frequency__ (in Hz). You will usually find an early reflection
+See the following topics:
-point at that distance from the woofer to your ears. You cannot and should not equalize for these.
+  * [[audio:rew:umik-1|Umik-1 Setup]]
+  * [[audio:rew:make-measurement|Make Measurements]]
+  * [[audio:rew:smoothing|Smoothing]]
+  * [[audio:rew:time-alignment|Time Alignment]]
+  * [[audio:rew:averaging|Averaging]]
+  * [[audio:rew:minimum-phase|Minimum Phase]]
+  * [[audio:rew:copy-measurement|Duplicating Measurement]]
+  * [[audio:rew:save-measurement|Save Measurement for Rephase]]
+  * [[audio:rew:generate-eq-filters:Generate EQ filter]]
+  * [[audio:rew:overlays:Overlays]]
 ==== Save project ====
 Hit Save filter settings to file to save REW EQ filter (use XML format to imported into rePhase).
 Save your work under File/Save All Measurement