> Using .mp3 to archive is a BIG mistake, it's a lossy format - that
> is, when .wav has been compressed to .mp3, a good portion of the
> information is "thrown away"
Tim,
That's the theory. I do theory but I am practical as well. The way I
am recording - long runs of wildlife and selecting - I simply can't
afford the time for daily selecting and discarding, or the cost of
storing Terabytes on HD.
I therefore did some experimentation before I settled on MP3/320. I
took a number of different WAV recordings and copied them to MP3/320.
I then subtracted the original and listened to the differences. MP3
encoding does at least three things: 1) it moves the time scale and
adds a slight "reverberation " effect 2) it adds artifacts 3) it phase
shifts.
If you do this test at a low bit rate like 128bps, you can hear these
effects without doing the subtraction, but at 320bps, these
distortions are below the natural background, natural reverb and I
defy anyone to detect the slight phase shifting. Has anyone checked
out the phase shifts from stereo mics? It is in the S signal and
completely swamps any subsequent MP3 phase shifting.
When I take a selection and process it, of course I go back to WAV.
Several generations of MP3 even at the top bit rate will show up. And
the best thing about all this it is that I ma the only one who has
heard the original mixer sound so you have to take my word for it. :-)
WAV compression by sampling is not lossless as I have said previously,
but the distortion is below normal audible limits. For my field
recordings, MP3/320 is also below practical audible limits. If I was
recording high quality music or speech (even more difficult to record
well) in perfect silent acoustics I would prefer WAV at 96Ks/s and 24
bits, in other words ridiculously high quality, but I am not and I
don't.
As a practical man and primarily a pragmatist, I am very happy to pass
on my archives to the next generation as MP3's, warts and all. The
warts include anthropogenic noise, unwanted species and just managing
to miss that perfect moment because my recorder only has a 1 second
pre-record. I want a 1 minute pre-record. :-(
BTW I quoted optical storage as the likely best archive medium as this
is what long term libraries are using. As for hard drive magnetic
storage, I've had too many corruptions to even trust a single drive
for daily backing up, so I back up on two drives. One of these
garbaged itself last winter.
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
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