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

[Markus Seeber]

On 11/21/2016 12:33 PM, Gerhard Zintel wrote:
> 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.
Additional filtering in this case would only be necessary when
converting the sample rate between the audio file and the target output
sample rate. If both are the same, we should be able to get "precise"
output. (neglecting eventual numerical issues from converting floating
point to integer samples and vice versa, which are not that relevant in
the square wave case anyway)