At 4:42 PM -0500 7/25/07, Bruce wrote:
>I wanted to put my two cents into the 24-bit discussion.
>
>I think you are missing the real advantages of 24-bit over 16-bit for
>recording soundscapes. I see it as an advantage to record at lower levels
>than I would have using a 16-bit system. When recording nature sounds there
>is always the unexpected sound that is louder than we would expect. To make
>best use of a 16-bit system, you would have to play with gain controls to
>achieve a signal of less than 0dB, but as close as you can to 0dB with out
>going over. You can be just happy with a setting, recording at -10 to -20db
>average, giving you around a 75dB dynamic range. Then a bird, a thunder
>clap, or other sound suddenly comes and clips the recording sequence, many
>times ruining the entire recording. Sometimes just a turn in the sound
>maker's body can clip the signal. With a 24-bit system, you can comfortably
>record at signal levels of -30 to -40dB average, while still getting over
>80dB of dynamic range. At those levels you are unlikely to have an inherent
>sound go into clipping, and gives you the added advantage of getting
>rare sounds when say an owl perches over your mic set-up. Post
>editing can bring the signals up to the level you want. I see 24-bit
>systems as an advantage
>to the recordist to use the added dynamic range, not necessarily as being
>better sound quality. With my 24-bit system, I set the gain to 30, 40, or
>50dB and walk away. No fussing around anymore, watching meters. I have
>colored LED meters I can watch through binoculars from a long distance away,
>just to make sure everything is cool. I will say that I found out how easily
>a signal can saturate, and how many mini-disc type level meters are too slow
>to know the event occurred. Any saturating, no mater how brief will cause a
>loss in quality, and that alone maybe the advantage of sound quality in a
>24-bit system. While out recording this Spring I can't tell you how many
>times my recordings would have been ruined by some birds that came in close
>to my recording set-up if I was still using a 16-bit system and flirting
>with saturation. Instead, those recordings came out perfect. Very few 24-bit
>recorders can achieve true 24-bit performance. The only ones that I know of
>are from Core Sound and Sound Devices, but their specifications are more
>based on part specification than actual measurements from completed units,
>but they seem to work ok. The one problem is that those recorders have
>higher noise levels at low gain settings, making the whole advantage
>somewhat pointless. All those other "24-bit" recorders from Zoom, M-Audio,
>Fostex, and others should be thought of as 16-bit recorders and no more. The
>advantage of the M-Audio is that it at least has a 24-bit input to bypass
>their poor inputs. I still use 16-bit recorders for capturing singles, as I
>can adjust gain on the fly to get the best results as I follow the subject
>around.
>
>Bruce Rutkoski
>www.natureguystudio.com
>
Hi Bruce--
I hear you about the potential advantages with dynamic range. My
test/report is intended as a response to Sound Devices' page
http://www.sounddevices.com/tech/24-bit.htm suggesting that 24 bit
recording offers less quantization noise than 16 bit recording under
practical, "real world" recording conditions.
Though amplitude quantizing noise is the only performance factor I
tried to study, one could deduce from the results that the dynamic
range with 16 bit recording might be more than sufficient for many,
many natural settings. My listening-based test suggests to me that if
I create a _16 bit_ file with a background level above (louder than)
-55 to -60 dBFS, I should be able to safely avoid any quantizing
noise. I suppose one can measure the background levels in one's 16
bit recordings after the fact for another sense of how much
"under-recording" in the field one can get by with. SD did produce
the quantizing noise in their test by "under recording" a very
significant amount. I tend to not under-record to great extent, but
should the circumstance call for lots of headroom, I'll be much less
hesitant to do it in the future-- even with 16 bits. From a small
amount of testing I've attempted with Richard's help, large digital
gain increases (like 30+dB) seem capable of altering qualities in a
recording so one might want to factor this into one's gain strategy
as well. Rob D.
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