I've enjoyed this thread.
Two subjective experiences I've had lately have prompted a shift in
which gear I use to record.
I've been doing sound effects work lately with some minidisc-recorded
sounds. I've discovered that pitch shifting, particularly extreme
pitch shifting, say slowing down a metallic sound by a factor of 8,
makes the compression artifacts much more audible for certain types
of sounds.
Given: The ATRAC process (or any perceptual coding process) does
result in artifacts being present in the decoded signal. Also given:
the codec process is designed so that these errors will occur at
places in the sound where the majority of listeners will be the least
likely to hear them, according to statistically developed
psychoacoustic models.
If the speed of playback of the decoded signal is varied, the
psychoacoustic model is shifted outside of it's design and the
process becomes more audible.
I've also noted, in careful listening, that certain types of
broadband sound are more likely to exhibit compression artifacts with
minidisc. I've noticed it particularly with closeup ocean waves:
acoustic energy spread all over the spectrum from deep bass to
ultrasonic, with lots of textural detail such as individual splashes.
The artifacts sound like a swirlyness, a lack of solidity, and what
I'd describe as a fuzzing, blurring or rippling of the tactile edges
of the texture. The latter is consistent with "you will see
significant distortions (additional noise) around rapidly modulated
sounds." from Raymond Specht's compression effects page. (thanks!
very informative.)
After these experiences, I'm going back to linear PCM for certain
sound effects recording, esp. anything which will be pitch shifted,
and certain broadband sounds.
(one has to admit, in ways Tape, and I don't mean cassettes, has
digital beat out when it comes to varispeeding.)
However, Minidisc is just so convenient in certain ways that I
definitely can't see quitting it. Sometimes, just waiting for the
DAT machine to rewind and thread, or running out of batteries, or
carrying extra weight, means that the recording can't happen or will
be compromised.
Thanks Walt for pointing out:
>DAT is lossy compression, hard disk digital is lossy compression, every
>single digital sampling method for sound is lossy. The question is not
>is it lossy, they all are. The question is what does that mean. Saying
>it's lossy is just the beginning, not the end of the discussion.
and Dan Dugan for (semantics regarding "data" understood):
>Since ATRAC has higher fidelity than, say, pre-Dolby analog master
>tape recording (compare to 15 ips 2-track: better s/n, flatter
>frequency response, lower distortion, better group delay), one could
>ask "what percentage of the data does tape recording throw away?"
We're imperfect beings using imperfect tools. No recorder/playbacker
chain is going to put you in the original acoustic environment. For
me, an important part of the craft is understanding the tools so they
can be best chosen and used in the service of whatever it is that
needs to be done.
-jeremiah
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jeremiah lyman moore | san francisco | sound+media |
http://babyjane.com/timeweb/
http://northstation.net/ organic, mechanized, organized sound
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