On Wed, Dec 08, 2010 at 05:00:34PM +0000, linuxdsp wrote: > James Stone wrote: >> On Wed, Dec 8, 2010 at 3:49 PM, Gabriel M. Beddingfield >> <gabrbedd@xxxxxxxxx> 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 >> _______________________________________________ >> Linux-audio-user mailing list >> Linux-audio-user@xxxxxxxxxxxxxxxxxxxx >> http://lists.linuxaudio.org/listinfo/linux-audio-user >> > > 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. > I have a slightly different question: I need to convert a non-balanced consumer-grade headphone input (from a laptop or iPod), to a non-balanced consumer-grade amplifier (Cambridge SoundWorks).... but with complete ground isolation. I'm guessing a simple transformer should do the trick, but the question is: WHICH transformer? What should the specs be in order to get the impedance right for both sides? -ken _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
