Some fiddling with the journal+issuetitle
bibmacro alongside with some formatting directives should get things as intended. Notice I had to make some decisions regarding the order of other fields you didn't consider in your example, with repercussions on punctuation. I also use babel to get localized bibstrings such as "Nr.".
\RequirePackage{filecontents}
\begin{filecontents}{\jobname.bib}
@Article{asmz,
author = {Hans Zimmer},
title = {Minimal music},
journal = {Some journal},
year = {2013},
number = {12},
pages = {40-41},
}
\end{filecontents}
\documentclass{article}
\usepackage[style=authortitle]{biblatex}
\usepackage[ngerman]{babel}
\usepackage{csquotes}
\renewbibmacro{in:}{}
\renewbibmacro*{journal+issuetitle}{%
\usebibmacro{journal}%
\setunit*{\addcomma\space}%
\printfield{issue}%
\setunit*{\addspace}%
\usebibmacro{date}%
\setunit{\addcomma\space}%
\iffieldundef{series}
{}
{\newunit
\printfield{series}%
\setunit{\addspace}}%
\printfield{volume}%
\setunit{\addcomma\space}%
\printfield{number}%
\setunit{\addcomma\space}%
\printfield{eid}%
\setunit{\addcolon\space}%
\usebibmacro{issue}%
\newunit}
\DeclareFieldFormat[article,periodical]{date}{\mkbibemph{#1}}
\DeclareFieldFormat[article,periodical]{volume}{\mkbibemph{\bibstring{volume}~#1}}
\DeclareFieldFormat[article,periodical]{number}{\mkbibemph{\bibstring{number}~#1}}
\DeclareFieldFormat[article,periodical]{pages}{\mkbibemph{\mkpageprefix[bookpagination]{#1}}}
\addbibresource{\jobname.bib}
\begin{document}
Let's cite! \footcite{asmz}
\printbibliography
\end{document}