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What's the
difference: Dynamic vs lossy audio
compression?
People mix up the two types of audio
compression all the time. Dynamic
range and lossy compression are very
different things.
Dynamic range compression squashes
soft-to-loud volume shifts. This
form of compression has been used by
recording, mixing and mastering
engineers for decades.
Other than bona-fide audiophile
recordings, most of the music you
hear has been dynamically
compressed--which isn't necessarily
a bad thing, as dynamic range
compression adds punch, presence,
and impact to music.
It's just that over the past decade
or so the trend is to over-compress
dynamics, so not only has music lost
most of its natural soft-to-loud
dynamics, but nuance and subtle
detail are missing as well. The
loud-all-the-time aesthetic is
boring.
Recordings with less compression
have lower (quieter) overall volume,
so if you go from listening to
maximally compressed contemporary
recordings to something with less
compression you need to turn up the
volume to compensate for the
difference.
As a consumer of music, you don't
have the option of buying
uncompressed music. If the engineers
squashed the soft-to-loud dynamics
out of the new Lady Gaga record
there's no way of getting them back.
Once sound is compressed, you can't
decompress it. If you want to hear
music with less compression, buy
original pressings of 1960s or 1970s
LPs. Yes, some of those will be
compressed, but less than
contemporary recordings.
On the other hand, you don't have to
buy lossy compressed music, at least
as long as CDs are made. I'm talking
about lossy audio compression here,
but lossy compression is also used
to compress video, streaming media,
still images, telecommunications,
etc. Lossy audio compression reduces
the transmission bandwidth
requirement of digital audio streams
and the storage size of audio files.
For music, MP3s intentionally "lose"
sounds that the MP3 software
designers deemed to be inaudible. In
the real world, the amount of
compression and the applied bit rate
determine how much audible sound is
lost by compression. At 128kbps,
it's easy to hear the losses, those
MP3s sound harsh, grainy and crude
compared with CDs, which are
completely uncompressed. Other forms
of lossy compression include AAC,
Dolby Digital, and DTS.
At 320 kbps, the difference between
MP3 and CD sound is barely audible;
you really have to listen carefully
to hear it. Listening on a train,
plane, bus or car I doubt you could
hear the difference. At home, played
over a decent stereo system in a
quiet room, the CD would sound a bit
clearer.
And now the really bad news.
If you buy iTunes or Amazon MP3
files you're getting dynamically
compressed AND lossy compressed
music. Congratulations, you're
getting the worst of both forms of
compression! You can avoid lossy
compression by buying the CD, but
chances are it will still be
dynamically compressed.
Thanks to Steve Guttenberg for this
article. | 
