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PostPosted: January 8th, 2019, 12:36 am 
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Joined: July 25th, 2013, 9:41 am
Posts: 33
I'm not getting good results while taking measurements.

Specifically, it appears the Impulse Response has a slight "DC offset". This is causing low-end frequency (i.e., less than 1,000Hz) response to be irregular.

If anyone uses it locally, I'm hoping they could help


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PostPosted: January 8th, 2019, 7:29 am 
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Joined: January 15th, 2015, 7:19 am
Posts: 813
Location: Baltimore MD
This looks like interesting stuff.
Did you build the measurement box. I am trying to understand the need for it.
I use trueRTA with Berlinger mic and an M audio usb mic preamp off my laptop.
I also use pink noise to measure freq response. I have never been very successful using pulse.
Also true RTA cannot do impedance measurement


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PostPosted: January 8th, 2019, 9:40 am 
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Joined: February 28th, 2013, 3:31 pm
Posts: 1091
I have replaced LAUD with ARTA and have been using it for some time, My interface from analog to USB is the Focusrite Scarlett 2i2. It works well but I did have an offset problem at one time when I went from an unbalanced signal lead to the balanced input to the2i2. I found that I had to use a shorting TS to RCA adapter. Apparently if one side of the balanced was left open it created the offset.

The interface between the ARTA test setup and the USB interface serves two functions. First it protects the interface from going up in smoke if an inadvertent signal gets too high. Second, it allows you to adjust the gain going into the interface. For example if you want to do a high power amplifier test the attenuation in the interface brings the signal level down to an appropriate level. I don't use the ARTA recommended interface because it uses zeners for protection which have non-distinct knees leading to potential errors. Using my own I was also able to calculate the divider values taking into account the actual input impedance of the 2i2. I did an article in Speaker Builder back in 1999 with the box being used with LAUD. It is still relevant with exception of the divider values. I'm including a copy of that article.

Please let me know if you have any questions.


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PostPosted: January 8th, 2019, 9:43 am 
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Joined: February 28th, 2013, 3:31 pm
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Sorry but the article file is just over 2Mb which is too big for this forum. If you send me a PM with your email address I'll send it to you.


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PostPosted: January 8th, 2019, 1:22 pm 
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Joined: July 25th, 2013, 9:41 am
Posts: 33
tomp wrote:
Sorry but the article file is just over 2Mb which is too big for this forum. If you send me a PM with your email address I'll send it to you.


Tom - just sent you a PM.

Thanks,
D


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