RT60 measurement

Samavio

Member
Thread Starter
Joined
Aug 21, 2017
Messages
18
How can one measure room reverb time in REW (RT60). Do I have to record an impulse and open it in REW or can REW handle it directly via a umik1 mic ?
 

Wayne A. Pflughaupt

Moderator
Staff member
Joined
May 21, 2017
Messages
243
Location
Corpus Christi, TX
My AV System  
Preamp, Processor or Receiver
Yamaha RX-Z9 A/V Receiver
Main Amp
Ramsa WP-9440 Stereo Amplifier (for subwoofers)
Additional Amp
TIVO Premier TCD746320 (OTA TV tuner)
Other Amp
Nakamichi MB-1 Seven-Disc CD Changer
Universal / Blu-ray / CD Player
Pioneer BDP-23FD Blu Ray Player
Front Speakers
TASCAM SS-R05 Media Player/Recorder
Center Channel Speaker
LRS Electronics Human 61 Speakers (all channels)
Surround Speakers
Realistic Minimus 7 (front EFX speakers)
Surround Back Speakers
Custom Built-in Subwoofer with Dual Shiva 12"
Front Height Speakers
Yamaha YDP2006 Digital Parametric EQ (front mains)
Rear Height Speakers
Yamaha YDP2006 Digital Parametric EQ (subs)
Subwoofers
Adcom ACE-515 (for power management)
Other Speakers or Equipment
Chase Technologies RLC-1 (remote control for subs)
Video Display Device
Yamaha DT-2 (digital clock display)
Screen
Audio Control R130 Real Time Analyzer
Remote Control
Stock Yamaha Remote
Other Equipment
Pioneer PDP-5070HD Plasma TV
Hopefully John can verify, but I’m pretty sure REW can handle it with the mic (any mic can be used for acoustics measurements by the way, no calibration required). You don’t have to provide an external signal source.

Regards,
Wayne
 

Samavio

Member
Thread Starter
Joined
Aug 21, 2017
Messages
18
Hi John/Wayne, thank you for your response. Do I take a sine wave measurement at 75dB for REW to generate the RT60 graph or do I need an impulse like using 2 planks of wood to generate the sound ?

Also, with the latest version of REW is it possible for me to use the HDMI port in my MacBook Pro to connect to my processor and select individual channels within the 7.1 channels ?
 

Samavio

Member
Thread Starter
Joined
Aug 21, 2017
Messages
18
How do I interpret the RT60 graph, is it the average "Topt" value that I should be looking at ? The value are different along the single octave bands.
 

John Mulcahy

REW Author
Joined
Apr 3, 2017
Messages
1,619
You use the Measure button on REW to take a response measurement and REW does the rest, including extracting the impulse response and calculating the RT60 values. You can select individual channels on a Macbook provided the HDMI output is configured for multichannel in the Mac's Audio/Midi settings.
 

Samavio

Member
Thread Starter
Joined
Aug 21, 2017
Messages
18
Fantastic! - I've just discovered the data panel which presents information in a neat table. What should I be looking at or doing to get the RT60 of a room ?
 

John Mulcahy

REW Author
Joined
Apr 3, 2017
Messages
1,619
Not sure I follow, that data is the RT60 of the room. RT60 varies with frequency.
 

John Mulcahy

REW Author
Joined
Apr 3, 2017
Messages
1,619
If you want a single figure you can get that from the data panel of the Filtered IR graph (with no filter applied).
 

Samavio

Member
Thread Starter
Joined
Aug 21, 2017
Messages
18
Hi John, I'm learning how to use REW. Love the interface and how it works. Any references that show how to configure the Mac's Audio/Midi setting for REW ?
 

Matthew J Poes

Staff Writer
Staff member
Joined
Oct 18, 2017
Messages
1,827
If you post your results we can help you interpret them as well.

There are some issues with RT60 in small spaces so it may be helpful to look at both the Topt and EDT. EDT is another measure of decay but is not the same as RT60. Because energy decays so quickly in a small room, EDT may be more informative.
 

Samavio

Member
Thread Starter
Joined
Aug 21, 2017
Messages
18
John and Matthew, thank you very much.

Matthew, I will post my results and your help will be appreciated.
 

Samavio

Member
Thread Starter
Joined
Aug 21, 2017
Messages
18
By the way, is it best to use the center channel in conjunction with the subwoofer for the RT60 measurement ? The mic would be placed in the main listening position at ear level. Alternatively, I could take 4 readings around the listening area and average them. I guess spatial averaging enables better measurement repeatability.
 

Matthew J Poes

Staff Writer
Staff member
Joined
Oct 18, 2017
Messages
1,827
By the way, is it best to use the center channel in conjunction with the subwoofer for the RT60 measurement ? The mic would be placed in the main listening position at ear level. Alternatively, I could take 4 readings around the listening area and average them. I guess spatial averaging enables better measurement repeatability.
You can't get RT60 or decay from spatial averaging or from RTA measurements. You need to use impulse measurements. You can take a number of these, time align them, and then vector average them if you want to look at the average RT60 and Waterfall. That is a little complicated for what you are trying to do.

You only need the center (or any main speaker) if you want to look at RT60 since that is really only valid above where the subwoofer operates.
 

Samavio

Member
Thread Starter
Joined
Aug 21, 2017
Messages
18
Hi John, I've finally managed to get all my tools and connections in order:-

1. I am using REW V5.19 Beta 8 (Running JRE 1.8.0_102 64-bit on OS x 10.10.5.

2. I am using the Umik-1 USB mic.

My MacBook Pro Retina 15-inch has an HDMI port and I am using a long HDMI cable to connect my laptop to my processor. The processor is recognised and shows up in the Audio Midi Utility. HDMI device shows up in the list of devices to the left. However, the Master Volume control along with level controls for each channel (value and db fields and Mute check-box) are all greyed out. The same is the case when I choose the HDMI option under "Aggregate Device". I have included an image for your reference.

I need to be able to pick/mute channels and play REW test tones to them. I don't understand, what I am I doing wrong ?

Screen Shot 2018-05-26 at 6.16.01 PM.png
 

EarlK

Member
Joined
May 22, 2017
Messages
70
OSXHDMIDolbyDigital.png


If your setup is anything like the above pic then unplug the HDMI cable going to the TV, ( then power down everything ) and turn back on the AVR and the Mac Mini ( starting with the AVR ).

If that doesn't fix/activate the greyed out section ( in the Audio Devices panel ) then I'm out of ideas.

MacOSXDolby-2.png


:)
 

John Mulcahy

REW Author
Joined
Apr 3, 2017
Messages
1,619
What is the aggregate device for? Not sure why you wouldn't just use the HDMI output directly.

It doesn't matter whether the volume controls in Audio Midi setup are active or not, they aren't used by REW. Just select the individual channels in REW.
 

louisa.chanx

New Member
Joined
Jun 10, 2019
Messages
3
Hi,

I'm new with REW and I got similar question about RT60 measurement.
List the equipment first:
Soundcard: Asus laptop built-in (Conexant)/
An active speaker connects to Asus laptop 3.5mm output/
Umik-1 mic connect to Asus laptop USB port

Question about RT60 measurement:
1) Do I need to calibrate umik-1 microphone before the measurement? I have my owned SPL meter, but the SPL value must include A-weighting or C-weighting or Z-weighting, can i use this meter?
2) From discussion above, it looks like I just need to start a frequency response measurement then REW will calculate RT60 for me, right? Why RT60 can be measured by this way?
3) How to calculate RT60 from T20, T30 and EDT?

Look forward to hear back, thank you.

Regards,
Louisa
 

John Mulcahy

REW Author
Joined
Apr 3, 2017
Messages
1,619
The UMIK-1 comes with a calibration file that includes a sensitivity figure, if you load the file in the REW mic/meter preferences and select the UMIK as the input device and input REW will show a calibrated SPL figure. REW generally prompts you for that if it sees a UMIK connected when it starts up and will take the necessary steps itself.

RT60 is calculated from the impulse response, the impulse response is calculated from the measurement.

T20, T30 and REW's Topt are all RT60 estimates based on different parts of the Schroeder integral derived from the impulse response. There is more on that in the help. EDT is the Early Decay Time, it is not an RT60 estimate but rather a figure for how quickly the sound initially decays.
 

louisa.chanx

New Member
Joined
Jun 10, 2019
Messages
3
Hi,

One more question -- How detail of RT60 that REW can tell?
Some DUTs have unstable results when doing acoustic test in our lab, we suspect that might be DUT is sensitive with reverberation. I hope I can see the RT60 is not so stable in DUT point and more stable in other points or more stable if i put some absorb material right next to the DUT.

Regards,
Louisa
 
Top Bottom