Re: [LAU] OT(ish): Connecting balanced out to line in

James Stone wrote:
> On Wed, Dec 8, 2010 at 3:49 PM, Gabriel M. Beddingfield
> <gabrbedd@email-addr-hidden> wrote:
>>
>> On Wed, 8 Dec 2010, James Stone wrote:
>>
>>> I guess in hardware?
>>>
>>> Thinking more about it, do I need to plug the DI out into a preamp
>>> before it goes into the line in for the soundcard? (the instrument is
>>> a bass guitar unamplified).
>> If you can, just skip the DI and plug the guitar straight into the sound
>> card's line-in.
>
> I've tried that before, but (at least with an electric (non-bass)),
> the sound was rather woolly and lacking in treble - I though due to
> the mix of Hi-Z and line level input.
>
> James
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If you are connecting a guitar to a soundcard input you will almost
certainly need some kind of DI box to provide the necessary high
impedance input for the guitar otherwise you will get a dull "woolly"
sound - as you describe.

A balanced line has three conductors instead of the usual two. These
are the screen, and the two signal wires. The signal wires carry the
audio signal, but in opposite polarity.

In a conventional balanced input stage, the two signal inputs are
subtracted from each other - and being of opposite polarity, the result
is the original audio. However, the important advantage of this method
is that any noise or interference induced on the wire(s) will be of the
same polarity on both signal conductors (in theory) and so will be
cancelled out (this is what common-mode rejection is all about).

You can get a signal for your single-ended input to the soundcard
between either signal phase and the screen. To avoid any phase
inversions, connect the positive signal out from the DI box (XLR pin 2)
to the signal in on your sound card input (Tip of the jack connector),
and the screen (XLR pin 1 ) to the ground on the soundcard input (Body
of the jack connector).

This is not the ideal way to convert between balanced and unbalanced
signals, but it will provide a working solution. There's some more info
here:

http://www.rane.com/note110.html

As for whether the signal level will need more amplification, that
depends on the DI box. If you can feed a line level mixer input, then
probably not, but try it and see.

Mike

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Received on Wed Dec 8 20:15:04 2010