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REW measurements
Old 15th September 2013
  #1
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Mctwins's Avatar
 

REW measurements

Hallo!

I downloaded the REW 5.01 version and using ASIO mode with Cubase LE5 and measurerd my room and notice that if you set higher samplingrate from 256k to 1M the peak distortion will dissapear before the actual Impulse in Filtered Impulse Response and Impulse response.

This is how my soundcard Tascam US-122 looks like in REW's Spectrum using Blackman-Harris 7 window. Measured in loopback mode.

.....and my Filtered Impulse Response measured in 1M sampling there is no distortion.

Regarding the mic dbx RTA-M there is no calibration file neither is it for my EMC8000 mic. There is no use for it. I measured with the dbx and EMC mic and there was no difference in the freq reponse, so just measure away without the calibration file for the mic.

Most importantly is do do a loopback measurement and calibrate the soundcard.
Attached Thumbnails
REW measurements-tascamjspectrum.jpg   REW measurements-prx600rew.jpg  
Old 16th September 2013
  #2
Gear Guru
 
Glenn Kuras's Avatar
Please post the IR file. I would like to view it in my program.

Thanks!
Old 16th September 2013
  #3
Gear Guru
What?

McT, the THD shown is 0.0150% Hardly significant.
More importantly, Loopback Correction is absolutely not needed for everyday measurements. But a cheap mic without a Cal file is almost useless for HF.

DD
Old 16th September 2013
  #4
Gear Maniac
 

It doesn't disappear, it just moves further back in time. The location of the distortion images depends on the sweep rate.
Old 16th September 2013
  #5
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Mctwins's Avatar
 

Quote:
Originally Posted by JohnPM View Post
It doesn't disappear, it just moves further back in time. The location of the distortion images depends on the sweep rate.
Yes, I have notice it when I change the sweep rate. I understand that it dosen't disappear, but, does it mean that the measurement itself is less infuenced by the distortion when using higher sweep rate?

Is it correct that higher sweep rate is more demanding for the computer/processor to work harder?
Old 17th September 2013
  #6
Gear Maniac
 

Quote:
Originally Posted by Mctwins View Post
does it mean that the measurement itself is less infuenced by the distortion when using higher sweep rate?
No, the distortion images are excluded by the IR window, they don't affect the displayed responses.

Quote:
Is it correct that higher sweep rate is more demanding for the computer/processor to work harder?
Not really, a longer sweep uses more memory but not enough to be a big deal.

Just for correctness: a longer sweep has a lower sweep rate
Old 20th September 2013
  #7
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Mctwins's Avatar
 

Quote:
Originally Posted by JohnPM View Post
No, the distortion images are excluded by the IR window, they don't affect the displayed responses.

Not really, a longer sweep uses more memory but not enough to be a big deal.

Just for correctness: a longer sweep has a lower sweep rate
Thanks John...

I understand that now and did more test and realized that it is important to do the Check Level procedure and when this was done, the distortion was gone in all sweep level from 128k to 1M. To me, it is very important to do soundcard calibration and the Check Level. This can be seen in the Scope graph if the signal is good or not.

It seem that the Scope graph disappers, it has to be seen directly after a measurement has been done, Why?? Why can't it be saved in the Scope graph so one can see it at later time. Hope you understand what I mean.

I also noticed that when a measurement is done it has to be dead quiet in the room before pressing the Start Measureing button. REW seem to be sensitive to surrounding environment.

There is differen't in settings on the knobs in my Tascam soundcard between REW and ARTA. The phones/line out is the same but the Mic In is diffren't

I will do more test and see if I have differen't readings if let my soundcard operate in the distortion area.

There is alot of things to do before making measurements
Old 20th September 2013
  #8
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Here one can see the difference between 35% and increase to 40% on my preamp volume level. The signal is good at 35% but it goes into clipping at 40%.
Attached Thumbnails
REW measurements-prx600vis35-.jpg   REW measurements-prx600vis40-.jpg  
Old 20th September 2013
  #9
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Mctwins's Avatar
 

Here is a measurement and when I clapped my hands during the measurement, it lookted like this.
All the measurement was catastrophic. In Filterd Impulse all the reading was in N/A and the Distortion graph was horrible.

So, don't fart when measurement is being done.
Attached Thumbnails
REW measurements-prx600handclap.jpg  

Last edited by Mctwins; 20th September 2013 at 11:11 AM.. Reason: spelling
Old 20th September 2013
  #10
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Mctwins's Avatar
 

I did a test with full knobs all the way up in my Tascam and the where distortion.

I have also notice if I move the mic closer to the speaker the signal in Scope isin't good. It means that if the mic is changed to another position a new Check Level must be done, either turn down the volume on AV receiver or knobs control on the soundcard or Levels on the computer so a good signal is achive in the Scope.

It is a good idea to check the Scope before presenting the data so everything is OK.
Old 20th September 2013
  #11
Gear Maniac
 

Quote:
Originally Posted by Mctwins View Post
It seem that the Scope graph disappers, it has to be seen directly after a measurement has been done, Why?? Why can't it be saved in the Scope graph so one can see it at later time. Hope you understand what I mean.
The raw sweep data in the scope graph consumes a lot of memory, so it is not retained. There are circumstances where it can be useful to have this, so one day there may be an option to retain the raw measurement.
Old 21st September 2013
  #12
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Mctwins's Avatar
 

Quote:
Originally Posted by JohnPM View Post
The raw sweep data in the scope graph consumes a lot of memory, so it is not retained. There are circumstances where it can be useful to have this, so one day there may be an option to retain the raw measurement.
Thanks, good to know.
Old 20th November 2013
  #13
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Mctwins's Avatar
 

Hallo!

Here is measurements from my Tascam US-122mkII soundcard connected in loopback.

SPL&Phase
Distortion
Waterfall
Scope

In the Distortion graph one can see that the fundamental is at 110dB and THD+second harmonics is at 30dB, (it is at the same level) and all other harmonics is below that. The red curve is the soundcards freq response and it derives from SPL&Phase and ALL SPL graphs. Why it is showing here, I don't know.

Just to verify that everything is OK with the soundcard when measurement is performed.

It schould be enough to see the distortion graph to see how the noise level is during measurement in the room.
Attached Thumbnails
REW measurements-tascamsplphase.jpg   REW measurements-tascamdistortion.jpg   REW measurements-tascamwaterfall.jpg   REW measurements-tascamjscope.jpg  
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