At 11:19 AM -0800 1/8/06, Dan Dugan wrote:
>Rob Danielson, you wrote,
>
>>A
>>recorder's overall mic pre gain can also play a role in final quality
>>in terms of generated bit depth saturation when ambient sound levels
>>are low.
>
>It isn't necessary to use the terminology "generated bit depth
>saturation." The noise floor of the recording process, as
>distinguished from the noise of the mic and the noise of the preamp,
>is determined by the A/D converter and the bit depth of the recording
>(16 or 24). The converter is always the limiting factor; I don't
>believe it's actually possible to record 24-bit sound from a
>microphone. 24-bit files, yes, but the actual dynamic range of the
>converter is rarely more than 21 bits (126 dB) in the most expensive
>gear, so the bottom bits of 24-bit files are filled with noise anyway.
>
>In my opinion it's more helpful to talk about the dynamic range of
>the converter in dB than to talk about bits. The bottom is noise,
>just like in analog audio; the only difference is that the noise can
>be uglier in digital.
>
>-Dan Dugan
>
Though the recording conditions I'm suggesting for judging "quality"
may be irrelevant to some recordists, I do think its beneficial when
recording ambience in quiet locations to achieve bit depths above the
sources of noise whether from the A-D converter, quantization, or
both. I'll do my best to clarify the significance. In this test,
http://www.uwm.edu/~type/Mic%20Preamps/MicroTrack_NH900_722Compare2.mov
the HiMD recorder at full gain using NT1A's->Rolls PB224->HiMD,
produced a sound file with 5% (peak) saturation from minimum urban
room ambience at 2 am. (I record each test for 20 minutes and use the
least saturated, 3 second passage in the test movie segment). The
MicroTrack 2496 at full gain produced a .23% peak for the minimum
background. After amplifying/equalizing the quiet background
recording to play at a comfortable listening level in my living room,
recordings made from originals with ~.23% peaks will exhibit less
clarity, less body and what sounds to me like more quantizing noise
compared to ones made from the recordings with ~5% peaks. The
additional noise could be from A-D too; that's a interesting
suggestion. The MT2496 is spec'd at 53dB of mic pre gain and the HiMD
gain has ~75dB gain referenced to the SD 722's 70dB of mic pre gain.
I'm not sure how to confirm this with math and likely there are
factors I'm ignorant of, but it sounds/seems like the 16 bit HiMD
recording at 5% might even possess more effective bits of resolution
than the MT2496's 24 bit recording at .23%.
Does anyone happen to know what the 671's mic pre gain is? Rob D.
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
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