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发表于 2009-12-14 00:21:44
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关于这几个选项，参考sox如下的说明， 摘自 rate.txt
All resamplers use filters that can sometimes create ‘echo’
(a.k.a. ‘ringing’) artefacts with transient signals such as
those that occur with ‘finger snaps’ or other highly percussive
sounds. Such artefacts are much more noticable to the human ear
if they occur before the transient (‘pre-echo’) than if they
occur after it (‘post-echo’). Note that frequency of any such
artefacts is related to the smaller of the original and new sam-
pling rates but that if this is at least 44.1kHz, then the arte-
facts will lie outside the range of human hearing.
A phase response setting may be used to control the distribution
of any transient echo between ‘pre’ and ‘post’: with minimum
phase, there is no pre-echo but the longest post-echo; with lin-
ear phase, pre and post echo are in equal amounts (in signal
terms, but not audibility terms); the intermediate phase setting
attempts to find the best compromise by selecting a small length
(and level) of pre-echo and a medium lengthed post-echo.
Minimum, intermediate, or linear phase response is selected
using the -M, -I, or -L option; a custom phase response can be
created with the -p option. Note that phase responses between
‘linear’ and ‘maximum’ (greater than 50) are rarely useful.
A resampler’s band-width setting determines how much of the fre-
quency content of the original signal (w.r.t. the orignal sample
rate when up-sampling, or the new sample rate when down-
sampling) is preserved during conversion. The term ‘pass-band’
is used to refer to all frequencies up to the band-width point
(e.g. for 44.1kHz sampling rate, and a resampling band-width of
95%, the pass-band represents frequencies from 0Hz (D.C.) to
circa 21kHz). Increasing the resampler’s band-width results in
a slower conversion and can increase transient echo artefacts
(and vice versa).
If the -a option is given, then aliasing above the pass-band is
allowed. For example, with 44.1kHz sampling rate, and a resam-
pling band-width of 95%, this means that frequency content above
21kHz can be distorted; however, since this is above the pass-
band (i.e. above the highest frequency of interest/audibility),
this may not be a problem. The benefits of allowing aliasing
are reduced processing time, and reduced (by almost half) tran-
sient echo artefacts. Note that if this option is given, then
the minimum band-width allowable with -b increases to 85%.
[ 本帖最后由 yyhapril 于 2009-12-14 00:24 编辑 ] |
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楼主
发表于 2009-12-13 21:32:43
