[Tech1] More Audio Skulduggery

[Dave Plowman]

Really quite remarkable in some ways. Previous car had a CD autochanger 
which held 10 discs. This one has a single CD player - but a USB input 
that takes a memory stick. The one I'm using about the size of a 
thumbnail. And has about 100 CDs on it, all of which I transferred 
myself. And a prog (can't remember which one) added the track etc 
information automatically, which appears on the screen in the car. I 
find MP3 OK for car use. After all, we put up with cassette or 8-track 
at one time, if wanting to play our own music.
On 13/09/2022 12:28, Alan Taylor via Tech1 wrote:
 > To expand on what Nick said.  CDs do not incorporate digital audio 
compression ( but of course will faithfully reproduce any audio 
compression used in the recording ). If you use sufficiently good A-D 
and D-A converters, the reproduced sound should be pretty well 
indistinguishable from the original to most ears.
 >
 > Where you start getting audible differences is when digital audio 
compression is used.  Digital audio compression can drastically reduce 
the amount of data needed, which means that more audio can be stored in 
a given amount of memory, or for streaming and broadcasting, less 
bandwidth is needed to transmit it.
 >
 > Compressed formats include MiniDisc, or for computer storage, MP3 and 
AAC. DAB radio uses digital compression too.  A typical MP3 file might 
need less than 20% of the data used  by a CD.  Streaming might squeeze 
what would originally be 100kB into less than 15kB. Obviously when 
you’re throwing away  80-85% of the original data, something has to give 
and the reproduced audio is sufficiently different that an untrained ear 
can detect the difference in A/B comparisons, but will most likely 
regard the reproduced audio as being acceptably good if listened to in 
isolation. A small reduction in quality would be a sensible trade off in 
return for storing much more music on a portable device, or having more 
radio channels available.
 >
 > Digital audio compression cleverly exploits a number of 
psychoacoustic techniques in order to mask what it’s doing.  Because 
different tricks are used to fool the ears and brain by different 
compression systems, you can’t simply compare the number of bits, sample 
rates, or megabytes used in order to deduce that one should sound better 
than another.  What you hear does not necessarily relate to what you can 
measure.  If you want to know more, try doing a search for ‘how digital 
audio compression works’ and choose an article which suits your 
preferred level of detail.
 >
 > Alan
 >
 >> On 13 Sep 2022, at 10:21, Nick Ware via Tech1 <tech1 at tech-ops.co.uk> 
wrote:
 >>
 >>  That was minidisc.
 >> N.
 >> Nick Ware - Sent from my iPad
 >>
 >>> On 13 Sep 2022, at 10:37, Pat Heigham via Tech1 
<tech1 at tech-ops.co.uk> wrote:
 >>>
 >>> 
 >>>
 >>> Correct me if I'm wrong, but I believe that coding the audio onto 
CD dispenses with frequencies that are 'masked' by stronger levels.