fast_coefficient_to_dB() returns a lower bound value, unsuitable
to catch audio peaks. The difference to 20*log10 is as large as 0.4 dB!
The effective speedup of fast_log10 compared to log10f is marginal
(sweep of all 24bit values)
i686 (1.6GHz Intel core): 2.36 [times faster]
x86_64 (core2 2.4GHz): 1.63
x86_64 (I3 2.80GHz): 2.03
the execution time of one log10f() averaged over a
sweep of all 24 bit values
i686 (1.6GHz Intel core): 0.131 usec
x86_64 (core2 2.4GHz): 0.033 usec
x86_64 (I3 2.80GHz): 0.044 usec
PeakMeter::run() is called from dedicated non-rt, no harm done.
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