> I am interested is VBR encoding so when I discovered LAME I started to
> play
> with it.
>
> For relative low quality I used -V 7 and didn't specify a minimum bit
> rate.
> To increase the quality I changed to -V 5 and added -b 64 (or something
> comparable). After upgrading from 3.50 to 3.58 I saw that a low pass
> filter
> was applied (cutting above 15,xxx Hz and decreasing above 12,xxx Hz) in
> this case.
>
> My first question is: is this automatic filter also in 3.50 (there was
> no
> output on the screen that told me about the filter in this version).
>
No, in 3.50 there was no automatic filter, but the sfb21 (16kHz) cutoff
for VBR quality settings lower than 3, (4-9)!
Since 3.55 this automatic filter is active depending on the compression
ratio, and therefore the bitrate (-b option) and sampling frequency.
I plugged the information print in, as I introduced the lowpass filtering
option in version 3.57.
> I discovered that this low pass filter was induced by the bit rate
> setting
> and independent from the VBR quality setting. I thought that the point
> where this filter isn't used is somewhere around 112.
>
> When I want to encode a file containing some difficult/dynamic parts and
>
> some easy parts using VBR I have the following options:
>
> lame -v -b 80 -h file.wav file.mp3
>
> in this case the low pass filter is used so especially the dynamic parts
>
> aren't at best
>
> lame -v -h file.wav file.mp3
>
> no low pass, but the easy parts may have a to low bit rate
>
> lame -v -b 128 -h file.wav file.mp3
>
> no low pass, no low bit rate for easy parts, but file size is bigger
> then
> necessary (getting a smaller file is the most important reason for
> encoding
> it to mp3, isn't it?)
>
> So my second question is how to control (or disable) this filter
> manually?
>
To be sure to get the full frequency range, I suggest using -k and
--lowpass 999.
I think we should change the -k option, to not only disable the sfb21
cutoff, but all kind of automatic filtering.
>
> Marc
Robert
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