Roger,
Here is a page that looks at the numbers for the 670/671:
http://www.avisoft-saslab.com/tutorial_mic_recorder.htm
It appears they both have the same gain stages (48 dB XLR gain, then
attenuating recorder gain controls, as confirmed by the spec sheets on both
recorders). Avisoft demonstrates that 24-bit recording (671) adds nothing to
the signal quality of most available mics, and that both machines adding 0.2
to 0.5 dB noise to most mics (according to calculations following Rane Note
148, http://www.rane.com/pdf/note148.pdf). Only if you are using a mic in
the 5 dB self noise range will you significantly detect preamp noise (1.8
dB) on a Marantz recorder. To use a very quiet mic you'd need something like
a 722 (-130 dBu self noise, contributing 0.2 dB noise to the mic signal).
I've just been running over these figures this weekend to calculate if I
should get a 722 and Rode NT1-A mics (or similar) for canyon recording.
Bruce Wilson KF7K
http://science.uvsc.edu/wilson
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