From: Vangelis forthnet Sent: Monday, July 17, 2017 21:24
... If you are referring to the original *low radiomodes as fetched by GiP,
then, and someone correct me, please, if I'm wrong, I believe 48.0kHz SR
applies to hardware/software media players which are capable of reproducing
the SBR portion of the HE-AACv1 encode; for SBR incompatible players, only
the LC portion is played back at half the SR, i.e. 24.0kHz (resulting in
most higher frequencies of the spectum being muted...).
Thanks for that, Vangelis. I have just found this in Wikipedia which
confirms what you say.
https://en.wikipedia.org/wiki/High-Efficiency_Advanced_Audio_Coding
"MPEG-2 and MPEG-4 AAC LC decoders without SBR support will decode the AAC
LC part of the audio, resulting in audio output with only half the sampling
frequency, thereby reducing the audio bandwidth. This usually results in the
high-end, or treble, portion of the audio signal missing from the audio
product."
That is something I didn't know. It would seem that for many players there
is a heavy penalty in using AAC with bitrates below hlsaacstd, dafstd and
hafstd, because the *med and *low modes use SBR.
That was an aside. My original question was why the BBC was using a 44.1kHz
sampling rate for its podcasts (which are MP3) instead of standardising on
48kHz throughout. Dave Lambley thought the reason might be that the LAME
encoder had been tuned for a 44.1kHz sample rate. There are certainly posts
in hydrogenaudio which support that. One on the dbpoweramp forum said there
were dire consequences of encoding a 48kHz sample rate as 320kbit/s MP3.
https://forum.dbpoweramp.com/showthread.php?14876-terrible-sound-quality-with-lame-mp3-48Khz
All those posts are 10 to 14 years old, so I don't know if they still apply.
There is no mention of it on the Wikipedia and Sourceforge LAME pages.
https://en.wikipedia.org/wiki/LAME
http://lame.sourceforge.net/about.php
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