Jim Lesurf wrote:
In article , DAB sounds worse
than FM wrote:
Dave Plowman (News) wrote:
In article , DAB sounds
worse than FM wrote:
Well, I've argued this issue over and over, and have yet to be
convinced in the slightest that Radio 3 should have a 50% higher
bit rate than Radios 1 & 2. Given the following reason, I really
do not have a clue how you can actually argue that Radio 3 should
have a far higher bit rate than Radios 1 or 2:

Clue. Look at the dynamic range of the samples on your website.
R1&2 - about 3 dB. R3 - about 25.


Exactly! It is the narrow dynamic range that makes R1 and R2 more
difficult to encode than R3.

I bet that's confused ya!

It has certainly puzzled me. Can you explain your reasoning and
define what you mean by "more difficult"?


The noise to mask ratio (NMR - noise (error) energy to energy under
masking curve for each subband) gives a measure of coding head-room, and
you want it to be as low as possible (i.e. noise as far below the
masking threshold as possible). Because Radios 1 & 2 and all the pop
stations have audio processing applied then the spectrum tends to be
wide and flat, which tends to result in aa lot of remaining frequency
components after the psychoacoustic model has produced the masking
curves to throw away the inaudible subbands. The same is not true for
classical music, because its spectrum isn't as flat, and on average less
frequency components remain after masking. Therefore, for a given bit
rate, there are more bits per post-masking frequency component for Radio
3 than for Radios 1 & 2, thus the NMR is superior (lower) for Radio 3,
because the noise energy is the quantisation noise, which decreases as
the bits per frequency component encoded increases.


FWIW I have no experience of DAB. But with freeview the times I
(think!) I may have noticed problems with R3 are mostly when the
sound levels are quite low. e.g. Strings playing very quietly. i.e.
at levels well below what I hear on R2.


Dynamic range and sound level for MPEG-encoded audio are irrelevant,
because the MPEG encoder changes the sample values to floating point.


--
Steve - www.digitalradiotech.co.uk - Digital Radio News & Info

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