[hatari-devel] STe DMA sound

[Vincent Rivière <vincent.riviere@xxxxxxxxxxx>]

Hello.

I'm not really satisfied of Hatari DMA sound emulation.
Basically, Hatari lacks a low-pass filter, which is a key signature of STe 
DMA sound at low frequencies such as 6 or 12 KHz.
This can particularly be heard in Lethal Xcess. Digidrums are very 
bass-boosted on real hardware. On the other hand, on Hatari (emulating sound 
at 44 KHz), we can hear some bogus-treeble sound. This is typical of samples 
upscaled with "nearest" algorithm, without filter.

I played Lethal Xcess with Effects only, and I recorded the sound with 
Hatari feature. See explosion sound as attachment.

I looked at it with Audacity.

First, see audacity1.png. We can see big stairs effect, which is typical of 
upscaling with "nearest" algorithm.
But if you look closely, there are big peaks at the beginning of each step. 
This is particularly visible when zooming more, see audacity2.png.

That's a complete nonsense. I can't understand where such peaks come from. 
They cause the apparition of bogus high frequencies, even more than standard 
upscaling. On the contrary, a normal low-pass filter would smooth such 
transitions. While currently, Hatari does the opposite, degrading the sound 
instead of improving it.

Definitely, Hatari STe sound can be improved.
I don't hear such problem in Steem.

--
Vincent Rivière

Attachment: explode.wav
Description: Wave audio

Attachment: audacity1.png
Description: PNG image

Attachment: audacity2.png
Description: PNG image