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1. Re: iRig pre

Subject: 1. Re: iRig pre
From: "John Crockett" naturalcontemplative
Date: Sun Jan 6, 2013 8:19 am ((PST))
Do we know which devices do this properly, handing the full signal to  
the unbalanced 3.5mm input? The 3.5mm output of the ART USBDualPre  
(which is far from ideal on many levels)  is 6dB lower than the  
balanced 1/4" output, so I imagine it is just dropping the - channel.

What is currently the best way to get a balanced XLR stereo signal  
into an unbalanced 3.5mm input, either mic or line? Do the SD preamps  
(mixpre, usbpre2) do this properly?

many thanks,

John

John Crockett


Let us live in harmony with Earth
And all creatures
That our lives may be a blessing

> 2.6. Re: iRig pre
>     Posted by: "Raimund"  animalsounds
>     Date: Sat Jan 5, 2013 9:20 am ((PST))
>
>> I just measured the iRig Pre this morning as well.  I got and EIN of
>> -112 dBu 20 Hz-20KHz unweighted (-114dBu A-weighted) with input
>> terminated at 150 ohms.
>
> Thanks for the confirmation, Rob!
>
> There is one thing that might explain the differences observed by  
> Marco between the iRig PRE and the ART Phantom II Pro:
>
> The iRig PRE internally probably subtracts the two output signal  
> rails (+ and -) of the balanced microphone from each other and  
> outputs the difference of both at its single-ended output. So, this  
> is obvioulsy a perfect conversion from the balanced input to the  
> unbalanced (single-ended) output.
>
> If one however connects the balanced output of the ART Phantom II  
> Pro to the single-ended input of the SONY PCM-M10 through the XLR  
> pins 1 and 2 only (leaving pin 3 open), then the output signal  
> level (as seen by the single-ended input) will be reduced by 6 dB  
> because the other rail is not being used. This would mean that the  
> effective sensitivity of the microphone is halved (from 20 mV/Pa to  
> 10mV/Pa), which would in turn increase the demands to the preamp  
> and may increase the overall system noise floor.
>
> For a mono recording setup, there would be a relatively simple way  
> to improve the final signal-to noise ratio by about 3 dB:
>
> 1. Connect the balanced output of the phantom power box to the  
> unbalanced stereo input as follows:
>
> XLR 1 <---> Sleeve
> XLR 2 <---> Ring
> XLR 3 <---> Tip
>
> This will record the positive output rail of the microphone to the  
> right channel and the negative output rail to the left channel.
>
> 2. Subtract the recorded stereo tracks from each other, which will  
> result in a mono track with doubled signal level for those signal  
> components that are present in both tracks. Because the noise  
> components of the both tracks are not related to each other, the  
> noise floor should only increase by 3 dB.
>
> Regards,
> Raimund







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