Best possible Audio-Output-Stage

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Re: Best possible Audio-Output-Stage

Postby joska » Thu Jul 30, 2015 6:59 am

I have never really noticed the bad sound quality because I've always used the mono output from the monitor connector which isn't nearly as loud as the stereo output.
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Re: Best possible Audio-Output-Stage

Postby joska » Thu Jul 30, 2015 3:40 pm

AtariZoll wrote:Now I can say that we should listen better to Amiga people and their comments about bad audio :D


The difference is quite dramatic. I played some of the tunes from the excellent "Stuck somewhere in time" music-disk on my A600 through a decent set of speakers, and then the same tunes on my unmodified STE. You can't even compare the sound quality, the Amiga sounds so much better.

However, when playing the same tunes on my modified STE the difference was negligible. Yes, there is a difference, but that is due to the replayer. With Paolo's modified Lance-player at 50kHz I'd say that the STE sounds just as good as the A600.
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Re: Best possible Audio-Output-Stage

Postby troed » Sat Aug 01, 2015 11:16 am

AtariZoll wrote:After all seen, I think that Atari screwed it seriously. That -12db for PSG should be always active. Those who made my STE mix-fix can activate -12db for PSG via SW. But it can be overriden by some SW. So, best would be to swap lines leading to pins 4-5, 25-26 - then default Microwire setting (in TOS too) will set -12db for PSG.


Will that accomplish mostly the same thing as this modification? I read your thread around the STE mix-fix with interest and I agree it seems Atari had a "proper" design in mind and just failed to implement it. Maybe they never even understood the intended design didn't make it into production.

It would explain why the STE default sound output is at a too high level.

/Troed

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Re: Best possible Audio-Output-Stage

Postby AtariZoll » Sat Aug 01, 2015 11:55 am

I think that it is good fix for too loud YM sound. DMA audio is silencer by some 12 db .
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Re: Best possible Audio-Output-Stage

Postby troed » Sat Aug 01, 2015 1:25 pm

AtariZoll wrote:I think that it is good fix for too loud YM sound. DMA audio is silencer by some 12 db .


I guess my question really was if it's only YM-output that's "too loud" on the STE, and that in reality what nada-san found and fixed is the same thing as you found: Atari really intended for YM to be -12db and if that fix is made then the STE regular output stage is "fine".

/Troed

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Re: Best possible Audio-Output-Stage

Postby Stefan jL » Sat Aug 01, 2015 1:44 pm

troed wrote:I guess my question really was if it's only YM-output that's "too loud" on the STE, and that in reality what nada-san found and fixed is the same thing as you found: Atari really intended for YM to be -12db and if that fix is made then the STE regular output stage is "fine".


I have not followed the discussion properly but afaik so is Nada-san's fix just lowering the soundoutput from the phono sockets and Atarizoll's mod is fixing the actual mixing of PSG and DMA, so the best thing is to do both mods to get quality sound... although all software (except Atarizoll's own) is only supporting the original PSG/DMA mixing.
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Re: Best possible Audio-Output-Stage

Postby troed » Sat Aug 01, 2015 3:58 pm

Stefan jL wrote:I have not followed the discussion properly but afaik so is Nada-san's fix just lowering the soundoutput from the phono sockets and Atarizoll's mod is fixing the actual mixing of PSG and DMA, so the best thing is to do both mods to get quality sound... although all software (except Atarizoll's own) is only supporting the original PSG/DMA mixing.


Right, I'll rephrase :) The default STE sound output is too loud - thus nada-san's fix. However, what AtariZoll found is that there seems to be a faulty implementation of the LM-mixer in Atari's design. Maybe it was Atari's intention all along to use the -12db option on the LMC for YM sound - thus the default STE sound (YM) output would (maybe) not be too loud at all?

So, if one does activate -12db as default - are the STE sound output levels still too high (distorted)?

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Re: Best possible Audio-Output-Stage

Postby AtariZoll » Sat Aug 01, 2015 4:12 pm

There is not much SW using STE DMA audio, and even much less is what uses simultaneously YM and DMA sound.
I think that we need some testings with proper audio sources. Since there is request for sine test and DMA playback proggie, I think that best will be to do both things at once. I have already code to playback 25 KHz STE mono sample via YM, so just need to generate some sine sample in proper formats.
So, I will work on it next week ..
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Re: Best possible Audio-Output-Stage

Postby dma » Sat Aug 01, 2015 4:19 pm

AtariZoll, i recommend you check some STe tunes composed on maxYMiser from the SNDH archive (check "DMA/" subfolder in various composer folders of the archive).
Those tracks mix YM and DMA sound. And some are featured in demos. Also this tendency is growing in ST(e) demoscene productions.

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Re: Best possible Audio-Output-Stage

Postby joska » Sat Aug 01, 2015 4:34 pm

troed wrote:Maybe it was Atari's intention all along to use the -12db option on the LMC for YM sound - thus the default STE sound (YM) output would (maybe) not be too loud at all?

So, if one does activate -12db as default - are the STE sound output levels still too high (distorted)?


DMA sound is way too loud on stock STE, and cause a lot of clipping and distortion when connected to a normal audio amplifier. The -12db fix by AtariZoll only affects YM output.
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Re: Best possible Audio-Output-Stage

Postby troed » Sat Aug 01, 2015 4:59 pm

joska wrote:DMA sound is way too loud on stock STE, and cause a lot of clipping and distortion when connected to a normal audio amplifier. The -12db fix by AtariZoll only affects YM output.


Thanks, that was what I was looking for (the distortion applying to both DMA as well as YM).

/Troed

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Re: Best possible Audio-Output-Stage

Postby Hippy Dave » Sat Aug 01, 2015 7:43 pm

Hi,

I looked at nada-san's schematic and the STE schematic to determine what was done to make the sound better.
The STE sound is actually not distorted... the sound is simply too loud for the device connected to the output jacks.

Here is a two wire (stereo) mod that will lower the output and invert the signal by 180 degrees:

- grab a STE schematic and turn to the page with the LMC1992.

- unsolder the lead of R520 (1K) that is connected to LMC1992, pin 14.
- use a wire to connect the R520 lead to U504B, pin 7 (U504 is LF347).

- unsolder the lead of R533 (1K) that is connected to LMC1992, pin 16.
- use a wire to connect the R533 lead to U504C, pin 8 (U504 is LF347).

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Re: Best possible Audio-Output-Stage

Postby joska » Sun Aug 02, 2015 9:05 am

Hippy Dave wrote:Here is a two wire (stereo) mod that will lower the output and invert the signal by 180 degrees:


I just tried this. Unfortunately it does not lower the signal enough, my amp is still clipping the signal.
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Re: Best possible Audio-Output-Stage

Postby joska » Sun Aug 02, 2015 9:10 am

troed wrote:Thanks, that was what I was looking for (the distortion applying to both DMA as well as YM).


I'm sure that a lot can be said about STE audio, but the main problem is that the output from the mixer is too loud. So it applies to both YM and DMA. AtariZoll's fix only applies to YM input to the LM mixer.
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Re: Best possible Audio-Output-Stage

Postby AtariZoll » Sun Aug 02, 2015 12:01 pm

I made some simple test SW and measured output levels on STE and Falcon .

AUDTEST.ZIP


Voltage levels measured on Mega STE RCA and Falcon 3.5 mm, without load:

PSG : MSTE - 1.2 V , Falcon 160 mV
DMA: MSTE - 1.35V, Falcon 1 V

PSG is silenter as normal as it is sample playback via tables. Visible is that on Falcon it is aprox 6x lower than on STE - and that ratio is exactly what missing on STE for proper PSG and DMA audio mixing.
In any case, this are pretty high amplitudes. and go thru only 1K resistor. So, not intended for some high sensitive, high impedance input. But are OK for usual PC line input as I see .

What to do if there is distortion, overdrive ? I think that simplest way is to add external dividers in both channels. No need to open machine, and 2 smaller resistors can fit in RCA connector . One res. go to signal (conn. middle), other end to second res. and cable, second res.'s other end to ground. 1K and 150 ohm will give approx. 6x lower amplitude.
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Famous Schrodinger's cat hypothetical experiment says that cat is dead or alive until we open box and see condition of poor animal, which deserved better logic. Cat is always in some certain state - regardless from is observer able or not to see what the state is.

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Re: Best possible Audio-Output-Stage

Postby joska » Sun Aug 02, 2015 1:29 pm

AtariZoll wrote:What to do if there is distortion, overdrive ? I think that simplest way is to add external dividers in both channels. No need to open machine, and 2 smaller resistors can fit in RCA connector . One res. go to signal (conn. middle), other end to second res. and cable, second res.'s other end to ground. 1K and 150 ohm will give approx. 6x lower amplitude.


I actually ended up doing this, but inside the STE. Then I'm not dependant of some special cable to get correct amplitude.
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Re: Best possible Audio-Output-Stage

Postby junosix » Mon Aug 03, 2015 9:41 am

Really interested in this mod, do any of the methods detailed in this thread also get rid of the high-pitched squeal that a lot of (all?) STEs exhibit in the left-hand channel?

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Re: Best possible Audio-Output-Stage

Postby AtariZoll » Mon Aug 03, 2015 9:55 am

junosix wrote:Really interested in this mod, do any of the methods detailed in this thread also get rid of the high-pitched squeal that a lot of (all?) STEs exhibit in the left-hand channel?

Not sure what you mean under that, and I never heard some squeal. But it may be because of overdrive.

joska wrote:...
I actually ended up doing this, but inside the STE. Then I'm not dependant of some special cable to get correct amplitude.


It depends on what user may connect his STE: if there are multiple amplifiers, then better is to have separated cable with divider and without . All it costs really not much - for those with little soldering skill.
Famous Schrodinger's cat hypothetical experiment says that cat is dead or alive until we open box and see condition of poor animal, which deserved better logic. Cat is always in some certain state - regardless from is observer able or not to see what the state is.

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Re: Best possible Audio-Output-Stage

Postby junosix » Mon Aug 03, 2015 1:40 pm

I'll try to capture the audio of the left-channel squeal, should have a chance to this evening. It's quiet enough to be masked when audio is playing but is noticeable when nothing is playing. My STE has done it since it was new and I've noticed it on other STEs and have seen mention of it by others as well. Hopefully it is just an overdrive thing and these mods may cure it!

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Re: Best possible Audio-Output-Stage

Postby joska » Mon Aug 03, 2015 1:55 pm

junosix wrote:Really interested in this mod, do any of the methods detailed in this thread also get rid of the high-pitched squeal that a lot of (all?) STEs exhibit in the left-hand channel?


These mods does not remove the noise. I guess the noise is introduced before (or maybe in?) the mixer.
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Re: Best possible Audio-Output-Stage

Postby junosix » Mon Aug 03, 2015 2:58 pm

Ah, that's a shame. You get the left-channel squeal on your STE too? It drives me mental.

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Re: Best possible Audio-Output-Stage

Postby junosix » Mon Aug 03, 2015 4:17 pm

Here's an example of the squeal that I mean: https://dl.dropboxusercontent.com/u/294 ... squeal.mp3 (from an unmodified STE audio output via stereo phono).

Seems to do it out of both channels actually, but more evident in the left. Most noticeable from about 20 seconds in, you can even hear it through the music when it's quiet enough. Sounds like data leaking over the bus into the audio circuit as it has a kind of "Spectrum loading" sound to it at times. My STE has done this from new and I've noticed others have too.

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Re: Best possible Audio-Output-Stage

Postby joska » Mon Aug 03, 2015 4:35 pm

junosix wrote:Sounds like data leaking over the bus into the audio circuit as it has a kind of "Spectrum loading" sound to it at times. My STE has done this from new and I've noticed others have too.


Yes, I recognise this noise. My totally untested theory is that this is noise from the shifter. Would be interesting to pick up audio directly from the DAC and see if the noise is there as well.
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Re: Best possible Audio-Output-Stage

Postby AtariZoll » Mon Aug 03, 2015 5:08 pm

It is normal that there is some little noise in audio by computers. Removing it completely is not cheap.
And that audio is DMA or PSG ? For me it sounds as PSG .
Famous Schrodinger's cat hypothetical experiment says that cat is dead or alive until we open box and see condition of poor animal, which deserved better logic. Cat is always in some certain state - regardless from is observer able or not to see what the state is.

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Re: Best possible Audio-Output-Stage

Postby junosix » Mon Aug 03, 2015 5:35 pm

The sampled sound is being played over DMA (game is Obsession, STE only) rather than PSG. I understand it would be difficult to totally eliminate noise but compared to the Amiga it sounds excessive, particularly as it can often be heard through the music.


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