At the risk of making things worse, normalisation is a technical term,
perhaps the correct term I was looking for is replay gain.
The BBC 'normalises' it's output to ensure everything is at the same
apparent sound level (relative to other output).
I was suggesting that some sort of automatic gain control is deciding
that the output is too loud and automatically reducing the gain for the
rest of the output. This may be particular to the iplayer output, the
original or could be the result of many stages of processing (e.g
normalising and already normalised input).
But then I am sure the staff at the BBC are well aware of this, and it
may not be the issue.
http://en.wikipedia.org/wiki/Audio_normalization
http://en.wikipedia.org/wiki/Replay_Gain
"Replay Gain works by first performing a psychoacoustic analysis of an
entire audio track to measure peak levels and perceived loudness. The
difference between the measured perceived loudness and the desired
target loudness is calculated; this is considered the ideal replay gain
value (the target loudness of most Replay Gain utilities is 89 dB SPL ---
6 dB higher than the Replay Gain specification and SMPTE
recommendation[1]). Usually, the gain value and the peak value are then
stored as metadata in the audio file, allowing Replay Gain-capable audio
players to automatically attenuate or amplify the signal so that tracks
will play at a similar loudness level. This avoids the common problem of
having to manually adjust volume levels when playing audio files from
albums that have been mastered at different levels. Should the audio at
its original levels be desired (e.g., for burning back to hard copy),
the metadata can simply be ignored."
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