low-frequency noise

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StanZ
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low-frequency noise

Postby StanZ » Tue Mar 07, 2017 12:06 am

Hi
I have a noise under Steem boiler 3.90 or Steem SSE 3.91. I can't get rid off by the sound option. (only if muted) Win 7/64.
Boiler 3.90 on the screenshots, but I did a fresh install of SSE 3.91.
The noise is inaudible but sometime it makes clics.
steem_noise.png
steem_noise2.png


:cheers:
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Steven Seagal
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Re: low-frequency noise

Postby Steven Seagal » Fri Mar 31, 2017 10:16 am

Hi
Sorry to reply only now, but I don't get it, is it a buzz that is always present with all configs, all programs?
Other people would complain.
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Steem SSE: http://ataristeven.exxoshost.co.uk/Steem.htm

StanZ
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Re: low-frequency noise

Postby StanZ » Fri Apr 14, 2017 8:25 pm

Hi
I have it when I run Steem (and only), the noise is under GEM and any app with music or not, with all configs. It seems to die at 60Hz. I saw it first on my audio gear (led meter) the level change after a reset between 0 to -12 dB. I tried a good phone but I can't hear it. I'm thinking it could be DC offset. https://www.freelists.org/post/steem/steem-Extreme-DC-Offset-in-recorded-WAV,1

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Steven Seagal
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Re: low-frequency noise

Postby Steven Seagal » Sat Apr 15, 2017 7:41 pm

RE: the signed/unsigned discussion

The YM2149 is supposed to have DC offset.
But that's not the problem.
The problem is that when option 'Sampled YM2149' is checked, Steem uses a 16bit unsigned volume table for PSG sound.

steem_dc.png


I don't know how you convert this to a proper signed 16bit table with no DC offset. :?:
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Steem SSE: http://ataristeven.exxoshost.co.uk/Steem.htm

StanZ
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Re: low-frequency noise

Postby StanZ » Sat Apr 15, 2017 9:07 pm

Maybe someone will help on this. I only know that a classic (nonlinear) high pass filter could get rid of the DC offset, even at 10 Hz.

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charles
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Re: low-frequency noise

Postby charles » Sat Apr 15, 2017 10:02 pm

sample vision ,,or audicy can do simple conversions of sound formats
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Steven Seagal
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Re: low-frequency noise

Postby Steven Seagal » Sun Apr 16, 2017 7:00 am

We clearly have more than a little DC offset problem here.
The wave is one-sided, large, and shifted down to make room. Technically, it's signed, but if we eliminated the DC offset (by reducing values and shifting up), it would be unsigned (all values>=0).
It explains why there's a little click at start/stop.
But it sounds realistic when running.
In the CIA we learned that ST ruled
Steem SSE: http://ataristeven.exxoshost.co.uk/Steem.htm

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Steven Seagal
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Re: low-frequency noise

Postby Steven Seagal » Thu Apr 20, 2017 7:50 am

steem_sound_centred.png

PSG


steem_sound_centred_dma.png

DMA

OK I think I solved the DC issue, maybe some noise/clicks too, by reducing the range of the PSG tables. It is divided by 2.
I don't think the ST had real 16bit range anyway, right?
DMA sound is now signed.
PSG sound needs to be unsigned. I tried to make it signed, but it would fail on the "sync-buzzer" effect. I suppose this effect relies on the actual sound wave being positive.
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