Re: Apple and EMI

Jaimie Vandenbergh <jaimie@xxxxxxxxxxxxxxxxxxxxx> wrote:

That's a different thing though, that also drives me to distraction.
What you're hearing is audio compression, which is different to file
compression.

A fair number of things on telly these days appear to suffer from what
I would think of as the opposite of compression, but correct me if I'm
wrong. Compression raises the volume of quiet bits so that you get a
relatively constant noise level output, yes? Good for radio in cars.

A lot of TV seems to bang on the deadeners so that quiet parts gets
quieter, like when you turn Dolby C on for a tape that had no Dolby
encoding at all. It stifles subtle noises and sort of rounds the edges
of the sounds off, often removing the beginning and ends of words.

Yes, audio compression basically squashes the wave form to reduce the
dynamic range. It tries to make all the frequencies have the same
uniform volume, so as you say, the quiet bits get louder, and the loud
bits get quieter. It has the effect of making it all sound rather
'flat'.

The compression that is used in the AAC files is not the same thing, it
is simply reducing the size of the file for better transfer across the
net. This removes bits of data that it deems unessential to reproduce a
reasonable copy when it's played back.

You can possibly see this more graphically when you see image files
compared - RAW or TIFF against JPG for example. Just have a look at the
histogram for each. On the RAW you should see a nice wave form fitting
well in between the ends of the scale. This gives you a full dynamic
range. The JPG will likely be chopped off at one, or each end, of the
scale, this limits the amount of information you can see in the image,
and you will most likely see a less vibrant, and less contrasty image.
This is similar to audio compression.

File compression is where you see see similar looking images, but if you
look in detail at the JPG you will see some blockyness (artifacts) which
means there is data loss. MP3s and AACs are the same, you will get
enough data to hear the track, and most likely be quite happy with the
results. Use some decent equipment and you'll hear the difference.

I have a pair of Grado headphones, and my HiFi is fronted by a pair of
Castle Severns, and I have to say, that although I *can* hear a
difference between the AACs I get from iTunes, and an original CD
recording, I can only say they are 'different'. The iTunes tracks
produce a sound that I find quite acceptable, and for most of my
listening, they are now the bulk of my source material.

If you were to just listen to a track from your iTunes collection, and
be happy with it, why bother looking any further?

--
Andy Hewitt
<http://web.mac.com/andrewhewitt1/>
.

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