[LAD] [LAU] Computer noise, was: Ardour MIDI tracer

[Will Godfrey]

On Sun, 17 Aug 2014 04:21:09 +0200
Ralf Mardorf <ralf.mardorf at alice-dsl.net> wrote:

> On Sat, 2014-08-16 at 20:17 +0200, Dennis Schulmeister wrote:
> > On Sat, 16 Aug 2014 18:21:52 +0200
> > Ralf Mardorf <ralf.mardorf at alice-dsl.net> wrote:
> > 
> > > Increase the volume and you will hear digital noise from the analog IOs
> > > of a card inside of the computer. Move the mouse and extra noise will be
> > > audible, no MIDI is needed to get annoying noise. MIDI noise is very
> > > silent compared to mouse noise, but there is some noise.
> > 
> > That's exactly the noise I'm talking about. With ground-lift it goes
> > away. At least it did for me.
> 
> I'll keep it in mind and test it someday. The idea of a DI-box between
> analog out from the sound card and input of the mixing console is
> strange, but that's were the problem appears. Parasitic noise might
> disappear, but transformers of a DI-box likely will have negative effect
> to the sound quality. Is there a DI-box without negative effect to the
> sound quality?

You get what you pay for. An active DI with quality transformers can easily
give a flat 20-20 response at up to +24dBu and with THD better than 0.1 %.

I'm getting that at +10dBu with a home build using the the transformer makers
recommended schematic, and was quite astonished to be able to reproduce a
flat-topped square wave at 100Hz with no visible overshoot.

-- 
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.