Re: [MP3 ENCODER] default high pass filtering

[Istvan Varga]

Segher Boessenkool wrote:

> > On some signals, however, highpass filters can do bad things as > > well.
> > For example, after processing this file
> >     http://www.geocities.com/SiliconValley/Bit/5683/test1c.zip
> > with a 5 Hz highpass filter, the peak amplitude increased
> > to about 52000, resulting in lots of clipped samples.
> 
> True. But you should always adjust the volume to less than 100% before
> encoding, because the clipping happens anyway. Can be worse with a low > cut filter, 
>though.

Yes, low frequency "ringing" caused by the highpass filter
can do bad things on some signals (such as this test).

> Anyway, what filter is it? How sharp etc.

I used MiXViews (a sound editor) on Linux, elliptical filter with
these parameters:
    passband cutoff: 6 Hz
    stopband cutoff: 4 Hz
    passband ripple: 0.1 dB
    stopband attenuation: 90 dB
(note: I converted the signal to float format before filtering).

Btw. most mp3 encoders seem to have problems with the
4 short noises at the beginning of the file (pre-echo
is cleanly audible).
--
MP3 ENCODER mailing list ( http://geek.rcc.se/mp3encoder/ )