These are derived from single precision AudioParam values
and so there is little to gain from using double.
double has the disadvantage that values intended to be integer
frame counts are less likely to be integer. e.g.
(rr) print ((float)(128.0/48000.0))*48000.f
$91 = 128
(rr) print ((float)(128.0/48000.0))*48000.0
$92 = 127.99999862909317
(rr) print ((float)(128.0/44100.0))*44100.f
$93 = 128
(rr) print ((float)(128.0/44100.0))*44100.0
$94 = 127.99999765120447
(rr) print ((float)(768.0/48000.0))*48000.f
$95 = 768.000061
(rr) print ((float)(768.0/48000.0))*48000.0
$96 = 768.0000364780426
(rr) print ((float)(768.0/44100.0))*44100.f
$97 = 768
(rr) print ((float)(768.0/44100.0))*44100.0
$98 = 768.00002697855234
MozReview-Commit-ID: FlmZJeBjUYY
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