Piecewise item list in beamer with transparency

Question

I'd like to have a list in beamer that fits with the following requirements:

1. blank page
2. item 1 is shown
3. item 2 is shown and item 1's opacity is reduced to the beamer "standard"
4. item 3 is shown and item 2 and 1's opacity is reduced to the beamer "standard"
5. item 4 is shown and item .... and so on

What I have so far:

\documentclass[aspectratio=169]{beamer}
\usepackage[utf8]{inputenc} % UFT8x - danske bogstaver
\usepackage[T1]{fontenc}
\begin{document}
\begin{frame}
\begin{itemize}
    \item $x$-aksen: kemisk skift, elektrontæthed omkring det atom, som proton(erne) er bundet til
    \pause
    \item $y$-aksen: ækvivalente antal protoner
    \pause
    \item Intensitet $=$ areal (integral) under signal
    \pause
    \item Intensitet $=$ antal ækvivalente protoner
    \pause
    \item Kan ``mærke'' nærliggende protoner $\to$ opsplitning
\end{itemize}
\end{frame}
\end{document}

Gives me a list where they get covered one after another.

\documentclass[aspectratio=169]{beamer}
\usepackage[utf8]{inputenc} % UFT8x - danske bogstaver
\usepackage[T1]{fontenc}
\begin{document}
\begin{frame}
\setbeamercovered{transparent}

\begin{itemize}[<+->]
    \item $x$-aksen: kemisk skift, elektrontæthed omkring det atom, som proton(erne) er bundet til
    \item $y$-aksen: ækvivalente antal protoner
    \item Intensitet $=$ areal (integral) under signal
    \item Intensitet $=$ antal ækvivalente protoner
    \item Kan ``mærke'' nærliggende protoner $\to$ opsplitning
\end{itemize}
\end{frame}
\end{document}

Gives me a list where the first item is visible and the rest are semi-transparent in the start, and gets uncovered one after another.

Answer 1

The following uses the capability of action specifications (the bit after the | symbol) to enable what you want. These are described on page 88 of the beamer 3.33 manual:

\documentclass[aspectratio=169]{beamer}
\usepackage[utf8]{inputenc} % UFT8x - danske bogstaver
\usepackage[T1]{fontenc}
\begin{document}
\begin{frame}
\setbeamercovered{transparent}

\begin{itemize}[<+(1) | invisible@-+>]
    \item $x$-aksen: kemisk skift, elektrontæthed omkring det atom, som proton(erne) er bundet til
    \item $y$-aksen: ækvivalente antal protoner
    \item Intensitet $=$ areal (integral) under signal
    \item Intensitet $=$ antal ækvivalente protoner
    \item Kan ``mærke'' nærliggende protoner $\to$ opsplitning
\end{itemize}
\end{frame}
\end{document}

EDIT: the code now uses the incremental specifiers, instead of hard coded slides.