+
+\opt{play_frequency}{
+ \section{Frequency}\index{Frequency}
+   This is the sampling frequency used for the rockbox playback engine.  Audio
+   at a different sampling rate will be converted to this sampling rate prior to
+   mixing using a cubic Hermite polynomial resampler.
+   \note{For best quality and battery life, select the sampling rate used by
+   your audio.  This is typically 44.1kHz.}
+   \note{Opus files are always 48kHz.}
+}