[LAU] bit-transparent playback/recoding over AES using an RME 9632 card

[Gerhard Zintel]

On Monday 21 November 2016, Tino Mettler wrote:
> On Fri, 2016-11-18 at 11:30 -0600, Chris Caudle wrote:
> > On Fri, November 18, 2016 8:59 am, Tino Mettler wrote:
> > > Actually, a colleague of mine did exactly that in Windows,
> > > using another RME card.
> > >
> > > Here are example screenshots of the original and the recording:
> > >
> > > https://tikei.de/playback.png
> > > https://tikei.de/recording.png
> >
> > That looks correct.  Do you have pictures of your result?
>
> Hi,
>
> the recording.png is the result from recording the playback from
> playback.png. It should be identical for bit-transparency.
>
Be aware that a rectangular wave has infinite frequency components in 
its edges. In any real physical system you have to lowpass this 
signal (either the reconstruction and / or the anti-aliasing filter). 
After filtering into the frequency range of interest (smaller than 
half sampling frequency) the wave looks like what you show in 
recording.png.

This is in each case true for a analog out- and input. I assume that a 
digital connection as well has to filter the signal as well to stay 
in the allowed frequency band according to your sample rate. Others 
might skim in with more knowledge on the digital side.

Gerhard

PS: apply a lowpass filter in Audacity to your playback signal and you 
will see the effect.