似乎圆润点，滑点，密度好点，尤其中低频。
但大了那么多不太值得诶。
[ 本帖最后由 mifeng 于 2009-12-13 21:18 编辑 ]
这里有解释：
As Steve said it before me, it is different compared to video. But one thing is the same for both: the quality differs between several upsamplers or upconverters. I don´t know how video upconverters function so I´ll concentrate on Audio.
Mostly upsamplers are used to get around the limitations of a cheap or bad DAC. With limitations I mean that these DACs have a bad performance when anti-aliasing is performed. In order not to have aliasing effects in the listanable audio area (20 - 20.000 Hz) everything above must be eliminated. So every DAC uses a very steep frequency cut-off at 20.000 Hz. Sometimes these algorithms are not that good so in the end they are hurting the sound. With upsampling you shift this 20.000 Hz of anti-aliasing further away to 40.000 Hz where you can´t hear it anymore. What you can´t do of course is recreating a signal that came from an original 24/96 source that was downconverted to 16/44.1. An upsampler or resampler uses an interpolation filter in combination with an anti-aliasing filter and fills up the spaces between the original 44.1 kHz with zeros when upconverting to 96 kHz.
So, an upsampler really is an oversampling filter without the D/A converter, because that is also what oversampling does. That means you could have frequencies over 20.000 Hz, but they are erased because of the believe that they can destroy loudspeakers or create problems for the amplifier. With 95 % of upsamplers you have a frequency response that goes from 20 to 20.000 Hz - beyond that is nothing. With good upsamplers the quality of the outcoming signal is the same as the original 16/44.1 data.
However, some people in the industry always knew that there could be more. WADIA & Pioneer for example. The spline algorithm is nothing else as an oversampling filter where the following anti-aliasing filter is not steep anymore and very soft. There the aliasing components are deliberate. Aliasing mirrors the frequencies starting with 22.050 Hz up to the double amount of 44.100 Hz. The data mirrored is the data from 20-22.050 Hz. Pioneer called this "Legato Link". Wadia and Pioneer did this to improve impulse response. The major drawback of steep aliasing filters is audio impulse that has pre- and post-ringing, means it adds ripples to the audio signal just by filtering above 20.000 Hz. With things like Legato Link this could be avoided - in the end you´ll get a frequency response up 44.100 Hz (faked of course) and nearly perfect impulses.
There is only one resampler on the market that can be configured to achieve this thing written above: iZotope RX Resampler. With this you can shift the cutoff frequency up or down, influence the kind of ripple (more or less pre-ringing) and configuring the steepness of aliasing cutoff. It is fast and produces perfect results, it really is very good. You can also use it for re-creating your standard resampler like SSRC or else. Then it sounds like a very good version of these "normal" resamplers.
With original 24/96 data, downsampled with iZotope and then upsampled again with iZotope I was able to find a perfect configuration that actually "recreates" 60-70 % of the sound of original 24/96 material without the errors of bad up- or resampling (smearing, less precision). So I´ll say Upsampling CAN have a benefit - if you use the right tools. Have a look here for pictures and more description (I hope I´m allowed to do that): http://www.thesoundtrackzone.com/viewtopic.php?f=35&t=323
非即时软件升频 > 即时软件升频 > 硬件升频
原帖由 mifeng 于 2009-12-13 21:11 发表 http://bbs.headphoneclub.com/images/common/back.gif
似乎圆润点，滑点，密度好点，尤其中低频。
但大了那么多不太值得诶。
这个就不好说了，毕竟买硬盘总是更便宜的
现在CD机很普遍采用硬件升频了,象前不久我介绍的JVC Z999EX的Extended K2线路就是升频,天龙DCD2000AE的AL24 Processing也是升频,其他各家有各家的升频做法,但都在升频,很普遍了.
关键点在于升频算法的优劣. 好的升频,对声音提升相当大,而不好的升频,令声音不自然,出现一种人工味,处理味.
向大家推荐
非时实： izotope rx advance 升频。
foobar2000实时升频插件： 基于sox rate算法的： http://www.hydrogenaudio.org/forums/index.php?showtopic=67373
[ 本帖最后由 yyhapril 于 2009-12-13 22:50 编辑 ]
试了一下这个SOX RATE的插件。
请问里面的一些参数如何设置：
PASSBAND默认值是95％，是否可调得更大？
ALLOW ALIASING默认是不选，是否应打钩？
PHASE RESPONSE默认是LINEAR，是否应该调整？
原帖由 yyhapril 于 2009-12-13 22:46 发表 http://www.headphoneclub.com/bbs/images/common/back.gif
向大家推荐
非时实： izotope rx advance 升频。
foobar2000实时升频插件： 基于sox rate算法的： http://www.hydrogenaudio.org/forums/index.php?showtopic=67373
原帖由 frui 于 2009-12-13 21:19 发表 http://bbs.headphoneclub.com/images/common/back.gif非即时软件升频 > 即时软件升频 > 硬件升频 随着硬件性能的提高，非实时的算法就可能变成实时算法了，哇哈哈
关于这几个选项，参考sox如下的说明， 摘自 rate.txt
All resamplers use filtersthat cansometimes create ‘echo’
(a.k.a. ‘ringing’)artefactswithtransient signals such as
those that occur with ‘finger snaps’ or other highlypercussive
sounds.Such artefacts are much more noticable to the human ear
if they occur before the transient(‘pre-echo’) thanifthey
occurafterit (‘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
ofanytransientecho between ‘pre’ and ‘post’: with minimum
phase, there is no pre-echo but the longest post-echo; with lin-
earphase,pre andpost 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, orlinearphase responseisselected
usingthe-M, -I, or -L option; a custom phase response can be
created with the -p option.Note that phaseresponsesbetween
‘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
ratewhenup-sampling, orthenewsampleratewhen down-
sampling) is preserved during conversion.The term‘pass-band’
isused to refer to all frequencies up to the band-width point
(e.g. for 44.1kHz sampling rate, and a resampling band-widthof
95%,thepass-bandrepresents frequencies from 0Hz (D.C.) to
circa 21kHz).Increasing the resampler’s band-width resultsin
aslowerconversionand can increase transient echo artefacts
(and vice versa).
Ifthe -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 abovethepass-
band (i.e.above the highest frequency of interest/audibility),
this may not be a problem.The benefits ofallowingaliasing
arereduced processing time, and reduced (by almost half) tran-
sient echo artefacts.Note that if this option isgiven,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 ]
试了一下这个SOX RATE的插件。
请问里面的一些参数如何设置：
PASSBAND默认值是95％，是否可调得更大？
ALLOW ALIASING默认是不选，是否应打钩？
PHASE RESPONSE默认是LINEAR，是否应该调整？
PASSBAND可以调更大，Increasing the resampler’s band-width resultsin
aslowerconversionand can increase transient echo artefacts。
Allow Aliasing 选与不选， Ifthe -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;The benefits ofallowingaliasing
arereduced processing time, and reduced (by almost half) tran-
sient echo artefacts
PHASE RESPONSE默认是LINEAR，是否应该调整？ 可以调，
A phase response setting may be used to control the distribution
ofanytransientecho between ‘pre’ and ‘post’: with minimum
phase, there is no pre-echo but the longest post-echo; with lin-
earphase,pre andpost 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.
什么是最佳参数，没有定论吧， 还是得自已比较。
不会调， 用默认也是不错的选择。
[ 本帖最后由 yyhapril 于 2009-12-14 00:31 编辑 ]
保守派，还是稀饭 标准格式
原帖由 小白 于 2009-12-13 13:56 发表 http://www.headphoneclub.com/bbs/images/common/back.gif
试了一首歌曲,47.6M的文件被弄成142M的. 16/44100的抓轨文件,升频到24/88200. 文件扩大到原来的3倍. :L :L :L
PASSBAND可以调更大，Increasing the resampler’s band-width resultsin
aslowerconversionand can increase transient echo artefacts。
PASSBAND调大了，会导致更多的transient echo artefacts，这是负面的吧？正面作用是什么呢？
Allow Aliasing 选与不选， Ifthe -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;The benefits ofallowingaliasing
arereduced processing time, and reduced (by almost half) tran-
sient echo artefacts
看这个说法，似乎是选ALLOW ALIASING能够减少transient echo artefacts，这应该是正面的作用吧。那么会有什么负面作用呢？
原帖由 yyhapril 于 2009-12-14 00:28 发表 http://www.headphoneclub.com/bbs/images/common/back.gif
试了一下这个SOX RATE的插件。
请问里面的一些参数如何设置：
PASSBAND默认值是95％，是否可调得更大？
ALLOW ALIASING默认是不选，是否应打钩？
PHASE RESPONSE默认是LINEAR，是否应该调整？
PASSBAND可以调 ...
1。PASSBAND越大频率响应越高。注意不是192kHZ的95%而是源文件的频宽的95%.
2。Aliasing自己会造成失真，不建议选
哎，你们都不用cplay的么，早就用SOX了
一般推荐99%的频宽（再大得不偿失）、不允许aliasing，应该是SOX的较佳设置，PHASE一般设成linear。当然机器要够快，但是够快的同时功耗不能高。自己玩咯！
[ 本帖最后由 pig2man 于 2009-12-14 12:02 编辑 ]
下载试试。
