Re: [hatari-devel] YM2149 Anti-Alias Filter

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On 10/06/2012 23:27, David Savinkoff wrote:
Yes. By-the-way, the low-pass anti-alias cutoff frequency is not
critical as long as it doesn't filter the music, thus, a convenient
and existing filter is used. Note that this filter (and the previously
disabled filter) are an alternative to BLEPs.

This anti-aliasing makes an improvement to the sound. Listen to
P7ACTION (STE) and other tunes in 505's BLUBBER.PRG for

The pull-up and pull-down resistance are of significance when making
DSP filters; however, these resistances are usually the same. To
model the YM2149, one must do circuit analysis and go beyond what
is written in DSP textbooks. This exercise got me to 'at least' make
some personal discoveries which others can now ponder over.


thanks for the explanations.

While applying the patch, I noticed in Audio_SetOutputAudioFreq in audio.c :

        if ((ConfigureParams.System.nMachineType == MACHINE_ST) &&
                (nAudioFrequency == 44100 || nAudioFrequency == 48000))
                /* Apply YM2149 C10 filter. */
                UseLowPassFilter = true;
                UseLowPassFilter = false;

Should this be changed ? Should we use piecewise filter all the time ?


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