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P3 Adjustment for the average Hobbyist
P3 Adjustment for the average Hobbyist
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Old 12th July 2018, 04:46 AM   #11
PRR is offline PRR  United States
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Quote:
Originally Posted by silasmellor View Post
...I am not sure what voltage input these interfaces tolerate....
"Crazed musicians with no technical sense".

The 2i2 has the extra feature of the knob glowing red when input levels are "too high". So start low and come-up slow. Basic audio common-sense.

You could also read the well-hidden slim specifications:
Downloads | Focusrite -- "User Guide"

"Line Inputs... Maximum Input Level ...+22 dBu"

"dBu" is jargon for "dB re 0.775V". So 9.7V is specified max. Essentially equivalent to a plain opamp fed with +/-15V supplies, still a favored source in semi-pro audio. And well above typical Hi-Fi working levels.

Gain Range is stated 50dB, which would imply signals as small as 31mV could be brought-up to 0dBfs on the digit-stream. (However you don't get 50 smooth dB on a dollar potentiometer, it may be glitchy at the extremes.)
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Old 12th July 2018, 05:42 AM   #12
silasmellor is offline silasmellor  Denmark
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P3 Adjustment for the average Hobbyist
Quote:
Originally Posted by PRR View Post
"Crazed musicians with no technical sense"
Yeah that’s pretty close to hitting the nail on the head. I don’t come from an engineering background, but have recorded music with my wife (who is a real musician, so I know the interfaces well enough but have not really needed to know the maximum input voltages. Thanks for showing the way on that PRR.

Yes the behringer will work. It may have a higher noise floor, but it should be low enough for this use.
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Old 12th July 2018, 06:03 AM   #13
MEPER is offline MEPER  Denmark
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There are also at help menu in the ARTA software. If you click on this there are a lot of topics. One of them is how to perform measurements and how an anp should hook up to a sound card. They also show a schematic of a input protection circuit with a couple of z-diodes etc. It seems the ARTA software has a signal generator so this is used as input via the 2i2 to the preamp and then output from preamp is going back again to 2i2 and then hopefully something will show up in the FFT analyzer window. There are a lot of adjustments possible……..
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Old 12th July 2018, 06:03 AM   #14
wintermute is offline wintermute  Australia
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P3 Adjustment for the average Hobbyist
The important thing with the focusrite 2i2 is to ensure that the input is not referenced to ground. fully differential the distortion performance is very good. But if running single ended the distortion goes up significantly.

Using a SE to differential circuit on the input, or even just simply using a TRS plug with only T connected to hot and R connected to earth with no connection to sleeve should improve the results.

I made a simple breadboard differential to SE for the output, thinking the problem was output distortion when in SE mode but that was not enough to fix the problem, the input seems to be key to getting good results.

Tony.
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Old 12th July 2018, 10:54 AM   #15
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Electronic Equiptment - DIY soundcard scope probe

Visual Analyser details

Audio Spectrum Analyser - free software
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Old 12th July 2018, 12:55 PM   #16
wintermute is offline wintermute  Australia
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P3 Adjustment for the average Hobbyist
Example of the difference between balanced loopback and SE loopback on the focusrite 2i2.

I was going to post results with balanced to SE converter and TR connection comming back but I did not get any better than with just an SE loopback, so not sure what happened there as I was sure I had much better results in the past. I'll have to delve a bit deeper.

Balanced was done with physical volume control at max, arta generator output at -6db and input level pot set to get -9db

SE was done without changing anything except the loopback cable.

Tony.
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File Type: png 2i2_balanced_loopback.png (19.9 KB, 235 views)
File Type: png 2i2_Bal2_SE_TR.png (21.2 KB, 239 views)
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Old 12th July 2018, 01:27 PM   #17
Russellc is offline Russellc  United States
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Quote:
Originally Posted by MEPER View Post
There are also at help menu in the ARTA software. If you click on this there are a lot of topics. One of them is how to perform measurements and how an anp should hook up to a sound card. They also show a schematic of a input protection circuit with a couple of z-diodes etc. It seems the ARTA software has a signal generator so this is used as input via the 2i2 to the preamp and then output from preamp is going back again to 2i2 and then hopefully something will show up in the FFT analyzer window. There are a lot of adjustments possible……..
Nice. I will read that over this evening. Thanks everyone who has added to this topic, much appreciated!

Russellc
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Old 12th July 2018, 09:54 PM   #18
MEPER is offline MEPER  Denmark
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I just received the 2i2 I ordered. Drivers are installed and ARTA software can use it. When I started recording using a sine wave as output I can hear the sine if I plug in a headphone at the monitor jack on the front. ARTA of course only shows noise as nothing is connected to the inputs. Could be interesting to make a loop back and check the quality of the sine. Now there is some work to find connector adapters etc. so everything can be hooked up.
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Old 13th July 2018, 12:57 AM   #19
Russellc is offline Russellc  United States
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P3 Adjustment for the average Hobbyist
Quote:
Originally Posted by vdi_nenna View Post
Ok, I just have one bit of advise to people starting on using "P3".
Monitor the current draw across whatever resistor you used to adjusted the bias. I had a bad experience and it wasn't my own amp. I was helping someone else. It's real bummer.

Maybe not so much on preamps, but power amp's current setting needs to be watched and your P3 changes should be done slowly. I would still watch preamp current adjustment. Can't hurt.

I have 2 spectrum analyzer applications; one is more complicated than the other. The results are basically the same. The more complicated version allows for more adjustment of measurement, results and views.
Are you referring to monitoring the FE bias, the output stage bias, or both?

Russellc
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Old 13th July 2018, 12:59 AM   #20
Russellc is offline Russellc  United States
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Quote:
Originally Posted by MEPER View Post
I just received the 2i2 I ordered. Drivers are installed and ARTA software can use it. When I started recording using a sine wave as output I can hear the sine if I plug in a headphone at the monitor jack on the front. ARTA of course only shows noise as nothing is connected to the inputs. Could be interesting to make a loop back and check the quality of the sine. Now there is some work to find connector adapters etc. so everything can be hooked up.
Excellent. I am glad you have received your device and have started experimenting. So it begins.

Russellc
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