An observation of cd-mastering, 16-bit audio, and the "almost silent"
cd:
The bit depth of an audio file determines the number of different
possible volume levels in the file. A 2 bit audio file could have 4
levels (00, 01, 10, 11), a 4 bit audio file has 64 levels, etc.
A big deal is/was made in the microsound "scene" (or at least the
press) about "near-silent" cds, while at the same time, a big deal is
made about "proper monitoring", about wide frequency ranges, etc.
While recently working on mastering a new cd relase of mine, I had a
revelation about making music artificially quiet on a cd (by not using
all of the available dynamic range)... this is bad for sound quality.
why?
well, read this quote from a FAQ about 24-bit field recording:
"16-bit recordings are capable of a theoretical maximum limit of 96dB
of dynamic range. This means that a single wave could have up to 65536
discrete values that can be used to represent it. But if the same wave
recorded at 16-bit peaks at 48dB below its maximum possible limit,
then there would only be 256 discrete values that can be used to
represent it, taking advantage of only 8 of the least significant
bits. The 8 most significant bits would contain no information
whatsoever, and would remain unused. In the case of 24-bit recording,
you’d have a maximum of 16,777,216 values to choose from, and in the
case of a wave peaking at 48dB below its maximum possible limit, the
wave would still have 65536 possible discrete amplitude values that
could be used to represent it."
from http://www.24bitfaq.org/#Q0_1_1
So a really quiet microsound / lowercase cd that never hits 0db never
uses all 16 bits of it's available data. A cd that stays bellow 48b
(which is really quiet, I realize), is really just an 8 bit recording
with an additional 8 bits of silence dropped on top of it.
Any subtle decay in sounds, such as reverb tails, suffer the most from
this.
Why then, do microsound/lowercase cds come mastered quietly, rather
than having a command to the audience of "PLAY QUIETLY" (the inverse
of the all too common command to "play loud".)
most of the time, people just end up turning the cd up anyway....
note that, assuming I'm understanding this correctly, if you had a
very quiet 24 bit recording that never peaked above -48db, you could
normalize it to 0db and then drop it to 16bit with zero loss of
data/fidelity.
Anthony
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