iplayer audio to lpcm

[Jim Lesurf]

In article <E1XnuQp-0000HO-40 at bombadil.infradead.org>, Dave Liquorice
<allsorts at howhill.com> wrote:
> On Mon, 10 Nov 2014 17:41:05 +0000 (GMT), Jim Lesurf wrote:

> >> IMO any significant difference in sound is going to be down to
> >> relative codec efficiency, not due to huge differences in the TX
> >> chain. iPlayer desktop uses AAC-LC, DSAT is MP2 and AAC for HD, DTT
> >> the same albeit at lower bit rates.
> > 
> > In general terms, that's what I'd be expecting. Particularly when my
> > favourite source material for comparisons has tended to be proms
> > concerts where I can compare R3 with BBC4, for example. 

> <cough> False assumption that there is only one mix leaving site... or
> even that the same mics are being used across the different services.
> Particulary for broadcasts on BBC1/2, not so sure what happens for BBC4.

< cough syrup :-) > I know from measurement and from discussions with some
involved that for the Proms on BBC4TV they use the R3 feed for the music.
BBC1/2TV do their own things, though. At times, that shows up clearly in
terms of things like reduced dynamic range on BBC1/2.

So in general for R3 vs BBC4TV Proms the mains differences tend to be
due to the encoder type/settings choices and any resamplings for changes in
base sample rate. e.g the way they used to HF limit one route to force the
bits available to be devoted to describing lower frequencies with more
detail.

You can see various examples by measurement on my website. In some cases
people at the BBC also kindly gave me source copies as LPCM pre-encoders
for comparisons. (For some years they found me useful as a 'health check'
on what emerged at the user end of the chains. They've been very helpful.)

Some quite subtle differences can crop up at times. <pun alert!> e.g.
the 'time travel' I found one year. The best guess we reached for it
was the presence of asynch resamplers in a chain.

Jim

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