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Old 17th May 2010, 10:08 PM   #101
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Hi,

<<<<<<< Chapter 1/4 of ARTA user manual:

Delay (ms) - enters the delay in the measured system, i.e. delay from loudspeaker to microphone (used only in a dual channel mode).

Chapter 4/4:

In the ARTA, the referent position is sample index 300. In single channel measurement mode there is no reference zero delay position, and zero delay position is not fixed - ARTA always puts at referent position the first sample whose amplitude is 20dB below the impulse response maximum. >>>>>>>>>>>



-----------------> OK but while being in dual channel mode I'm unable to get correct times/distance from mic to measured driver! Why? How to proceed?

Thanks
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Old 20th May 2010, 05:07 PM   #102
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UP

Nobody?
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Old 26th May 2010, 10:27 PM   #103
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still nobody!
Maybe my question wasn't clear enough...
So: Is ARTA able to give us the time of the travelling sound between an impulse and the mic? Or is this question a nonsense because it cannot exist a fixed impulse time (no physical "beginning" of an impulse)?

Thanks
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Old 27th May 2010, 07:12 AM   #104
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Latest manual 1.6.1 Page 60 Chapter 4.5

4.5 System Delay Estimation
The fixed delay in some measured system, for example the delay of sound wave from loudspeaker to microphone, or delay in digital processing systems, can be easily estimated (to accuracy of one sample), from the position of maximum of the cross-correlation function of the system excitation and measured response.
The estimation of delay can be obtained automatically by clicking the menu command 'Recorder->Crosscorreletion/delay estimation' in Fr2 mode, after initial measurement of frequency response. That command opens the dialog box 'Input Channels Cross-correlation' as shown in Fig. 4.14.
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Old 27th May 2010, 10:05 AM   #105
Jmmlc is offline Jmmlc  France
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Hello,

If the impulse reponse has been acquired by the logsweep method and without the "center" option of Arta then you can use the mouse and move the arrow in order to place it at the beginning of the rise of the main pulse Then you can read the corresponding arrival time expressed in milliseconds near the bottom left corner ("cursor").

If the impulse response has been acquired by the logsweep method using the "center" option of Arta which allows to obtain additionally the distortion curves H2, H3 and H4, then:

after opening a .pir response impulse: using the mouse move the arrow in order to place it at the beginning of the rise of the main pulse and you can read the corresponding time expressed in milliseconds near the bottom left corner.

Remember this time t_read. Then the arrival time t_arrival you are looking for is the result of the formula:

t_arrival = t_read - 2721.354

t_arrival is expressed in milliseconds

Best regards from Paris, France

Jean-Michel Le Cléac'h
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Old 28th May 2010, 07:20 AM   #106
Jmmlc is offline Jmmlc  France
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Hello,

I forgot to mention that the formula I gave is for an record done using a "sequence length" of 256 k and a sampling requency of 48kHz.

As I only use that large sequence length I cannot say if the formula is valid for other sequence lengths...

Best regards from Paris, France

Jean-Michel Le Cléac'h


Quote:
Originally Posted by Jmmlc View Post
Hello,

If the impulse response has been acquired by the logsweep method using the "center" option of Arta...

... the arrival time t_arrival you are looking for is the result of the formula:

t_arrival = t_read - 2721.354

t_arrival is expressed in milliseconds
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Old 28th May 2010, 09:43 AM   #107
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Quote:
Originally Posted by Jmmlc View Post
As I only use that large sequence length I cannot say if the formula is valid for other sequence lengths...
No not valid.
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Old 28th May 2010, 10:45 AM   #108
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Hello guys,

As I am able to measure in dual channel mode, jerome69's advise works fine! Finally I got correct results using this method. Thanks Jérome!

Jean-Michel: I am unable to get correct times using your two single-channel methods even with the same sampling (48k)and length(256k)...Are you sure about?
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Old 28th May 2010, 11:57 AM   #109
Pano is offline Pano  United States
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BTW, why is ARTA cheaper in Euros than US dollars? Not taking current exchange rates into account?
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Old 28th May 2010, 12:28 PM   #110
Jmmlc is offline Jmmlc  France
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Hello,

I never use the 2 channels method (due to the added complexity). But as, in order to estimate the arrival time, a crosscorrelation seems to be performed between the ouput of the amplifier and the signal recorded by the microphone it is probably the best method as it will avoid artifacts due to the operating of the soundcard.

If a single channel is used we have to take in account some lattency between the input and the output of the soundcard and everyone will have to use a different formula...

Best regards from Paris, France

Jean-Michel Le Cléac'h






Quote:
Originally Posted by crazyhub View Post
Hello guys,

As I am able to measure in dual channel mode, jerome69's advise works fine! Finally I got correct results using this method. Thanks Jérome!

Jean-Michel: I am unable to get correct times using your two single-channel methods even with the same sampling (48k)and length(256k)...Are you sure about?
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