[MPlayer-dev-eng] [PATCH] fix for -srate bug

[Ed Wildgoose]

>>how the hell do you get aliasing when upsampling? aliasing comes from
>>downsampling without bandlimiting.
>>
>>rich
>>    
>>
>
>Sorry for jumping in here but I have a few comments:
>
>When doing upsampling the unwanted bands are called imaging bands. They
>have a similar effect as aliasing when downsampling. Unfortunately in
>both cases you have to filter _after_ the upsampler and _before_ the
>downampler, i.e at the high speed side. However, efficient realizations
>can be made by using a poly-phase structure of the aliasing/imaging
>filters. Maybe this is of small value here, since we are talking about
>conversions 44.1kHz to/from 48kHz, or?
>  
>

Sure they can.  I haven't done any extensive testing on resampling 
algorithms, so I can only speak from a theoretical angle.  However, I 
think the point is that your interpolation between points can easily 
(accidently) introduce frequencies which are outside of the desired 
frequency band, these then get folded back into the audible spectrum on 
the downsampling.

As I said, I have no practical experience comparing implementations, so 
I really couldn't comment on how audible this is with a certain 
implementation (as in here).

Ed W