[MPlayer-dev-eng] [PATCH] Proof of concept extrasurround plugin

[Anders Johansson]

Hi

> 
> 
> On Thu, 4 Apr 2002, Anders Johansson wrote:
> 
> > Try using my lowpass filter you find it in libao2/fir.h. It is
> > assembly optimized and quite easy to use. Have you read the specs of
> > how steep and how long the filter should be? Guess you will find them
> > in the dolby surround specifications. According to Steve Davies who
> > wrote the plugin the filter needs to be quite long to sound well. I
> > will be happy to help you out with using the FIR filter. We could
> > replace the other filters in this plugin as well while we are at it.
> 
> Hi - the thing with fir filters is that you need a lot of taps to get a
> steep roll-off at a low frequency.  That may be fine with the asm filter
> you wrote but my C version wouldn't be fast enough.
> 
> So I agree to replace the filter with yours.  I haven't looked at it.  One
> question in my mind is whether it will be compatible with the coefficient
> calculating that I do.

Filtertaps int16_t* normalized to +/- 32768 where pw[0] is the first
filtertap (will be multiplied with the latest value of x). I think my
C implementation is a bit quicker than yours as well cause I use a
linear buffer with double storage and you a circular one.

> > We might want to use this even if there is no surround sound
> > information just to generate the necessary sub-woofer channel. That
> > would make the sound a lot better on cheap surround sound systems,
> > where the front L and R speakers are small.
> 
> Don't speaker systems like that usually do that bass diversion anyway?  As
> you can tell I only have 4 speakers!

Depends on what kind of power amplifier that is used and if the
sound card has digital out or not.

> Steve

//Anders