25-Apr-2015: This is a summary in German language about analog audio interfaces. Based on excellent and essential papers of Bill Whitlock and Bruno Putzeys it explains why and how single-ended in- and outputs are a very fragile construct with obvious sonic deficiencies.
The paper was put together for the German speaking DIY-community and I keep updating it as I find new details worthwhile mentioning.

03-Aug-2012: Douglas Self presents extracts from his well done book about active cross-overs at the Burning Amp Festival 2011.
An anecdote about the book:
I was reading it around October 2011 partly during vacation on a scuba diving safari. One of the instructors was asking what thick a book I would read and I said that it had to do with loudspeakers, which was my hobby etc. And the guy was like...what, you can write a book about loudspeakers ?!? And I said: Weeellll, you is actually only about cross-overs for loudspeakers. And he was like...WHAT ?!? you can write a book only about cross-overs for loudspeakers ?!?
In the end I did not tell him that the book was actually only mainly about analogue active cross-overs for loudspeakers...J

Updated 01-Jun-2012 to add some better explanations and due to some interesting findings with Demokrit (originally posted 23-Nov-2011):
This is an interesting article by Alvin Foster, member of the Boston Audio Society (BAS). It was originally published in May 1999 in the BAS Speaker (BASS), which is the newsletter of the society (Volume 22, Number 2). The link embedded in the document was recently posted in a discussion at I have created the pdf with my comments and markups.
Over the time I have obviously come to many equal conclusions as the author.

Last updated 12-Mar-2024