Podcast sample rate

Dave Lambley dave at lambley.me.uk
Mon Jul 17 10:18:26 PDT 2017

On 17 July 2017 at 17:32, RS <richard22j at zoho.com> wrote:
>> From: Dave Lambley
>> Sent: Monday, July 17, 2017 15:43
>> There are also CODEC internals to consider. The LAME people used to
>> recommend resampling down to 44.1kHz before encoding, because that was
>> the sample rate they had done most of their tuning against.
> I didn't know about that recommendation and it may be what has influenced
> the BBC.  I have transcoded a fair number of 48kHz sample rate AAC files to
> MP3 using LAME with no audible problems.  That has mainly been at 128kbit/s.
> Maybe problems occur at lower bit rates.  At 48kbit/s Mediainfo shows the
> sampling rate as 48.0kHz / 24.0kHz.  I guess that means a Nyquist frequency
> of 12kHz.  Moneybox used to use a very low rate for its podcast.  I think it
> may have been a sample rate of 16kHz and a bit rate of 32kbit/s.

Surely a Nyquist frequency of 24kHz for a 48kHz sample rate? I don't
remember where I heard the "stick to 44.1" lore from, but Google has
turned up https://hydrogenaud.io/index.php/topic,9105.0.html

Yes, I'd have thought that any problems relating to tuning would
related to the psycho-acoustic stuff, and so would vanish given a high
enough bit rate.

>> For playback, 48kHz files are relatively rare outside video, and receive
>> less testing.
> A lot of audio is distributed on CD and of course the CD sampling rate is
> 44.1kHz.
>> My old Sony Ericsson phone, for example, would play back
>> 48kHz AAC with periodic digital splats.
> Was that a 48kHz problem or an AAC problem?  Some players are very fussy
> about the AAC they will play.  I used to have a DAB+ radio which would also
> record DAB+ stations in AAC.  It was a struggle to find a DAB+ station but I
> found one in Poland.  Playback of its own AAC recordings was fine.  It was
> also fine playng MP3 files from its microSD card.  When it played external
> AAC files there was warbling sound over the top.

I can't answer that as the phone sadly died. The files would have been
from get_iplayer in ~2010.


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