[hatari-devel] LMC1992 and Microwire emulation

npomarede at corp.free.fr npomarede at corp.free.fr
Sun Mar 7 20:35:51 CET 2010


On Sun, 7 Mar 2010, Laurent Sallafranque 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 ?

Hello,

I think we can find some pointers for this on the web, but this certainly 
requires more computations than a simple filter (fft or maybe some 
specific faster method ?)

>
> 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)

for the ym2149, volume is clerly not linear and the table is logarithmic, 
maybe you can use it as a starting point (there're only 16 values, but you 
can deduce a similar table for 256 values)

> Do you agree ?
>
> Could somebody compare volume in protracker in hatari and on a real ste ?

The real solution would be to play a constant sample sound (square wave 
consisting of values 127 and -127) at 50 kHz and then measure the output 
voltage on the audio out pin of the ste for example. By doing measures for 
32 different volumes or so between 0 and max, this should give the correct 
graph to extrapolate all values (that's the method used to get the 16 
volumes level of the ym2149)

Nicolas




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