[hatari-devel] LMC1992 and Microwire emulation

Laurent Sallafranque laurent.sallafranque at free.fr
Mon Mar 8 23:33:49 CET 2010


Another question :

Is there an order for effects computing ?

Should I compute volume before and IIR after, or IIr before and sound 
after ?

Regards

Laurent



David Savinkoff a écrit :
> Hi,
>
> A FFT is not the solution, an IIR filter is required. See:
> http://www.dspguide.com/
> for a freely downloadable book.
> My recommendation is to use a running average filter.
> This is similar to a FIFO, but where you add samples into
> a variable and subtract an old sample out every time you
> add a new one in. How many samples are averaged depends
> on the cut off frequency desired (this is a low pass filter) and
> the sampling frequency. To make a treble filter, subtract an
> averaged value from an input value. Note that the delay of
> the filter is considered to be half of the averaging length.
>
>
> Mar 7, 2010 09:18:03 AM, laurent.sallafranque at free.fr 
> <mailto:laurent.sallafranque at free.fr> wrote:
>
>     Hello,
>
>     I've added LMC1992 and Microwire emulation to hatari.
>
>     For now, Master volume, left volume and right volume are emulated.
>     Still to do : Bass and Treble.
>     Does it need a FFT and FFT -1 transformation or are there specifics
>     algorythms for bass and treble ?
>
>     I've done my tests with protracker Ste.
>
>     I think there's a problem anyway for both falcon volume table and ste
>     volume table :
>
>     I've used a linear volume table to calculate values from the min
>     to the max.
>     I think values should be calculated with a logarythmic algo.
>     (There's only values in the volume_table to change, nothing else)
>
>     Do you agree ?
>
>     Could somebody compare volume in protracker in hatari and on a
>     real ste ?
>
>     Regards
>
>     Laurent
>
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