REW Beta Release RT60 questions

[user44455555]

wy does it show Classic: No Data on EDT T20 T30 ? .I have done estimate IR but it was 0,1 sample diffrence and generate minimum phase. happen on all measures i do. low or high level

 

[John Mulcahy]

The classic results are generated by choosing the same octave fraction on the RT60 graph.

 

[user44455555]

The classic results are generated by choosing the same octave fraction on the RT60 graph.

thanks, i test now and notice when i choose in rt60 decay 1/1 or 1/3 it switches to same value in RT 60. but RT 60 is not able to do more than 1/3 . is this limit enhance in future ?

 

[John Mulcahy]

RT 60 is not able to do more than 1/3 . is this limit enhance in future ?

That limit was part of the reason for developing the RT60 Decay processing.

 

[user44455555]

That limit was part of the reason for developing the RT60 Decay processing.

Do you mean in the rt 60 curve is no higher resolution as 1/3 possible ?.
I think the RT60 much better to see where to place foam and basstraps as the rt60 decay because it work with overlays. rt 60 deay not. the resolution i think should be at least 1/6 to see more easy when diffrent foam positions change and compare results . I hear this before and later after measure i see that at 800 hz decay time (T30) of left speaker is double as right speaker in the result. but better resolution is better

or is there a way in REW to show in rt60 decay the diffrence of left right speaker measure only with calc funtion or so ?

 

[John Mulcahy]

Do you mean in the rt 60 curve is no higher resolution as 1/3 possible ?

Yes.

I think the RT60 much better to see where to place foam and basstraps as the rt60 decay because it work with overlays. rt 60 deay not.

You can choose the RT60 decay T60M parameter for the RT60 overlay just as you can choose any other.

 

[user44455555]

Yes.

You can choose the RT60 decay T60M parameter for the RT60 overlay just as you can choose any other.

The T60M in RT60 overlay choose did not show anything first, but i notice there need first press Generate in the RT60 decay page to see drawing in overlay. but it is great have high resolution. is it possible that this algo can also do a high resolution T30M ?. I think T60 is not so usefull in real life. . left and right speaker curve look as this on overlay in T60M . In Bass the SPL is reduce (noise -48 db) so can not get good dynamic also because of car traffic low rumble. but in T60M 800 hz is ok noise is -55 db. I dont want it make very loud when measure.

 

[John Mulcahy]

The T60M figure, like all the RT figures, is the time to decay by 60 dB. It does not require a noise floor at -60 dB, nor do any of the other RT measures, such as T20 or T30. You misunderstand the process, which is explained in the help.

 

[user44455555]

The T60M figure, like all the RT figures, is the time to decay by 60 dB. It does not require a noise floor at -60 dB, nor do any of the other RT measures, such as T20 or T30. You misunderstand the process, which is explained in the help.

the results i get with T60m look as the noise floor is too high in the bass, because lots diffrent in compare to T30(from RT 60 page) in bass. I read about T60 T30 T20 here

Reverberation Time

Typically, the ambient noise in a room (e.g. an apartment or office) would create a noise floor of 40-50 dB. To measure a decay of 60 dB from a sound source, we have to inject the sound at 75 dB (with 5 dB for the auto trigger and 10 dB headroom to the noise floor) above this noise floor. Creating such sound at 125 dB across the whole spectrum, and particularly at low frequencies, requires awfully high sound pressure and is often practically or even technically not feasible.

In practice, therefore, the standards ISO 3382-1 and ISO 3382-2 specify to measure the time taken for the reverberation to decay by 20 dB or 30 dB only. These readings can then be linearly extrapolated to a decay time of 60 dB.

 

[John Mulcahy]

Once again: T20, T30, Topt and T60M all give figures for the time to decay by 60 dB. They differ in how they calculate the figure. None of them require 60 dB SNR. Your assumptions about the impact of the noise floor are wrong.

 

[user44455555]

Once again: T20, T30, Topt and T60M all give figures for the time to decay by 60 dB. They differ in how they calculate the figure. None of them require 60 dB SNR. Your assumptions about the impact of the noise floor are wrong.

I have done tests and upload the mdat files. below you can see also on T30. below 100 hz the loudest measure have the shortest decay time. so my conclusion is, the lower volume measures have too few SNR. also the old T30 measure bring no better results. above 160 hz the loudest measure have the longest decay time. you can see in the FR. FR is identical, because i only increase volume on audio device and measure again. the old algo have above 180 hz too much jumps so seem not correct.

if the longer decay time at lower level below 100 hz is not too low SNR what can it be ?.

 

[John Mulcahy]

Your system has a strange echo at 40 ms and 80 ms that gets stronger with level and causes significant problems with RT60 calculation, it is abnormal. The 84 dB measurement shows it clearly:

 

[user44455555]

Your system has a strange echo at 40 ms and 80 ms that gets stronger with level and causes significant problems with RT60 calculation, it is abnormal. The 84 dB measurement shows it clearly:

View attachment 85756

maybe that it get higher on higher level happen becaue of treatment ? .because of more air pressure the foam did not absorb so much as with lower volume ?

at 84 db it is -26 db on 40 ms is 100 hz . and -52 db is 80 ms is 200 hz. is this not normal in higher levels on untreat rooms ?.o treatment work better on low volume. . i use 5 cm - 12 cm basotect.

at 72 db it is - 39 db.
at 78 db(which is my hearing volume) it is -33 db . so should be enough to calc T30

 

[John Mulcahy]

Those features are not normal, you should try and determine what in the system is causing them.