[hatari-devel] STE sound breakage with lower sound frequencies

[Laurent Sallafranque]

Hi,

 > Sound under 44 kHz is anyway rather ugly most of the time, so if no 
one objects, I think I will add a change to apply IIR filters only for 
"quality" output freq >= 44 kHz. Applying filters to lower output freq 
will just alter a sound that is already of poor quality (especially in 
ym mode only).

If there's no other solution, I agree for this change.

Laurent


Le 13/02/2011 20:10, Nicolas Pomarède a écrit :
> Le 08/02/2011 20:07, Eero Tamminen a écrit :
>> Hi,
>>
>> On tiistai 08 helmikuu 2011, Nicolas Pomarède wrote:
>>> Le 07/02/2011 23:15, Eero Tamminen a écrit :
>>>> I tried Utopos demo.
>>>>
>>>> If I use "--sound 11025" or "--sound 16000", there's just a short
>>>> "dup"[1] sound and then no sound at all.  With e.g. 22kHz or 48kHz,
>>>> sound works fine for STE emulation too.
>>>>
>>>> The issue happens also for Hatari from end of december and for Hatari
>>>> v1.4. Keyclick on STE TOS works for Hatari v1.4 even at 11025Hz
>>>> though.
>>>
>>> Yes, I can reproduce similar issues ; not related to my latest changes,
>>> certainly there since a long time and specific to dma sound.
>>>
>>> It seems that if Hatari starts with a too low freq then there's no 
>>> sound
>>> (changing sound freq with F12 don't correct it). But if I start Hatari
>>> in default mode (44.1 kHz) in my case and change freq with F12 to 
>>> 11025,
>>> I still get sound.
>>> Do you have the same behaviour ?
>>
>> Yes.  If I change the freq from options, there's no problem.
>>
>>
>>> So, it's not the freq change, but probably some inits based on the
>>> starting sound freq that are not correct.
>>>
>>> I'll try to give it a look later.
>
> Hello,
>
> I found the cause of the problem, it's the bass/treble filter.
>
> In previous version of Hatari (1.4) it was only applied when DMA sound 
> was on, but in rev 3159 laurent applied the patch submitted by david 
> to also apply the filter when DMA sound is off too and only ym2149 is 
> used (-> key sound under gem)
>
> This is the correct behaviour to apply the filter in all case, the 
> problem is that according to the comment by David "The tone control's 
> sampling frequency must be at least 22050 Hz to sound good".
> It seems that at 16 kHz or less, it just sound empty in fact :)
>
> You can test this is the cause :
> 1) in dmaSnd.c comment lines 355/356 to get key sound under gem again 
> when running "./hatari --machine ste --sound 16000"
>
> 2) in dmaSnd.c comment lines 491/492 to get dma sound under utopos for 
> example when running "./hatari --machine ste --sound 16000"
>
>
> David, is there a way to have the filter behave better when sound freq 
> is less that 22050 Hz without changing too much code ?
>
> We could build other filter tables in 
> DmaSnd_Init_Bass_and_Treble_Tables for lower ouput freq, but I'm not 
> sure this is necessary.
>
> Sound under 44 kHz is anyway rather ugly most of the time, so if no 
> one objects, I think I will add a change to apply IIR filters only for 
> "quality" output freq >= 44 kHz. Applying filters to lower output freq 
> will just alter a sound that is already of poor quality (especially in 
> ym mode only).
>
>
> Nicolas
>
>
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