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Last thursday or thereabouts I decided to sit down and fix the noise channel on my SMS emulator.

When I was comparing my emulator to a real SMS, however, I discovered that the frequencies for the
pulse channels were wrong (I don't remember if they were too low or too high).

It isn't a problem with my math (because the music is dead on for relative pitch, just not absolute pitch,
and because my NES emulator has the frequencies correct), so it has to be a mistake in one of my given
values.

I have been using the info from the file richard.txt in the S8-dev archives, which is almost entirely correct.
It is demonstrably wrong, however, in its suggestion of 125,000 Hz for the PSG clock (could this be the
correct value for a PAL or SECAM system?).

What is the correct value for an NTSC system?

--Nyef

Quote

> Last thursday or thereabouts I decided to sit down and fix the noise channel on my SMS emulator.

> When I was comparing my emulator to a real SMS, however, I discovered that the frequencies for the
> pulse channels were wrong (I don't remember if they were too low or too high).

> It isn't a problem with my math (because the music is dead on for relative pitch, just not absolute pitch,
> and because my NES emulator has the frequencies correct), so it has to be a mistake in one of my given
> values.

> I have been using the info from the file richard.txt in the S8-dev archives, which is almost entirely correct.
> It is demonstrably wrong, however, in its suggestion of 125,000 Hz for the PSG clock (could this be the
> correct value for a PAL or SECAM system?).

> What is the correct value for an NTSC system?

I *think* that you just add 17.5% of the PAL value to get the NTSC value. (21875 Hz?)
Don't flame me if I'm wrong ;-)
~unfnknblvbl

Quote

> --Nyef

Quote

> I *think* that you just add 17.5% of the PAL value to get the NTSC value. (21875 Hz?)
> Don't flame me if I'm wrong ;-)
> ~unfnknblvbl

> > --Nyef

isnt it 20%? 20% of 50 is 10, and 50+10 = 60
i do assume that pal is 50 hz and ntsc is 60hz - are those the correct exact hz?
anyways, wouldnt a pal system and a ntsc system sound the same (except for the tempo of the sound due to diferent timing of the Vint) ? here again i assume that the system oscalator is the same value between machines.

what is the clock frequency of the sms? its around 3.5 mhz, but what is it exaclty?

if we say its exaclty 3.5mhz, then
3500000 / 32 = 109375 which is around the 110khz mark. substitute the original clock value and it may be more accurate to the real thing.

one clock speed i have read was 3579540hz, but i found that the clock in a megadrive 2 i have ( its broken :( ) was 53.203mhz / 15 ( for z80 speed) which gives me 3546866hz which would alter the sound pitches..
hmm, i must get my original mega drive 1 back to see if sega changed the clocks between the two models, or perhaps the mega drives/genesises (which a powerbase converter) sound different to a sms..

Quote

> I have been using the info from the file richard.txt in the S8-dev archives, which is almost entirely correct.
> It is demonstrably wrong, however, in its suggestion of 125,000 Hz for the PSG clock (could this be the
> correct value for a PAL or SECAM system?).

> What is the correct value for an NTSC system?

> --Nyef

Quote

> what is the clock frequency of the sms? its around 3.5 mhz, but what is it exaclty?

XTAL1 is 10.7386 MHz. Divide by 3 to get 3.579533333333 (a close match for the NTSC color subcarrier, if anyone cares).

Quote

> if we say its exaclty 3.5mhz, then
> 3500000 / 32 = 109375 which is around the 110khz mark. substitute the original clock value and it may be more accurate to the real thing.

This sounds reasonable. I'll try it tonight to see if it's better than what I'm currently using.

Quote

> one clock speed i have read was 3579540hz, but i found that the clock in a megadrive 2 i have ( its broken :( ) was 53.203mhz / 15 ( for z80 speed) which gives me 3546866hz which would alter the sound pitches..

One of the signals in any NTSC color video game system has to come close to 3.579545 in order to work. It it's too far off the mark, the system doesn't work.

Quote

> hmm, i must get my original mega drive 1 back to see if sega changed the clocks between the two models, or perhaps the mega drives/genesises (which a powerbase converter) sound different to a sms..

Hrm... I'll have to try the power base again. And I'll see if any of the genesis systems I have have that 9-pin expansion connector while I'm at it...

--Nyef

The Game Gear clock is 3.579545 mhz. I don't know exactly the SMS, but it should be the same.
Game Gear is refreshed at 60 hz.

That is so true. Pal and NTSC games will play the exact same tones and frequencies but at a different
tempo due to the Vints. NTSC is 50 and PAL is 60.

Chris :o)

Author	Message
Nyef Guest	SMS PSG clock frequency? Posted: Tue Sep 07, 1999 5:20 pm
Nyef Guest	Last thursday or thereabouts I decided to sit down and fix the noise channel on my SMS emulator. When I was comparing my emulator to a real SMS, however, I discovered that the frequencies for the pulse channels were wrong (I don't remember if they were too low or too high). It isn't a problem with my math (because the music is dead on for relative pitch, just not absolute pitch, and because my NES emulator has the frequencies correct), so it has to be a mistake in one of my given values. I have been using the info from the file richard.txt in the S8-dev archives, which is almost entirely correct. It is demonstrably wrong, however, in its suggestion of 125,000 Hz for the PSG clock (could this be the correct value for a PAL or SECAM system?). What is the correct value for an NTSC system? --Nyef

unfnknblvbl Joined: 12 Jul 1999 Posts: 891	I think... Posted: Wed Sep 08, 1999 6:53 am
unfnknblvbl Joined: 12 Jul 1999 Posts: 891	Quote > Last thursday or thereabouts I decided to sit down and fix the noise channel on my SMS emulator. > When I was comparing my emulator to a real SMS, however, I discovered that the frequencies for the > pulse channels were wrong (I don't remember if they were too low or too high). > It isn't a problem with my math (because the music is dead on for relative pitch, just not absolute pitch, > and because my NES emulator has the frequencies correct), so it has to be a mistake in one of my given > values. > I have been using the info from the file richard.txt in the S8-dev archives, which is almost entirely correct. > It is demonstrably wrong, however, in its suggestion of 125,000 Hz for the PSG clock (could this be the > correct value for a PAL or SECAM system?). > What is the correct value for an NTSC system? I think that you just add 17.5% of the PAL value to get the NTSC value. (21875 Hz?) Don't flame me if I'm wrong ;-) ~unfnknblvbl Quote > --Nyef

Limbs a Flyin' Guest	Re: I think... Posted: Wed Sep 08, 1999 11:14 am
Limbs a Flyin' Guest	Quote > I think that you just add 17.5% of the PAL value to get the NTSC value. (21875 Hz?) > Don't flame me if I'm wrong ;-) > ~unfnknblvbl > > --Nyef isnt it 20%? 20% of 50 is 10, and 50+10 = 60 i do assume that pal is 50 hz and ntsc is 60hz - are those the correct exact hz? anyways, wouldnt a pal system and a ntsc system sound the same (except for the tempo of the sound due to diferent timing of the Vint) ? here again i assume that the system oscalator is the same value between machines.

Limbs a Flyin' Guest	Posted: Wed Sep 08, 1999 11:40 am
Limbs a Flyin' Guest	what is the clock frequency of the sms? its around 3.5 mhz, but what is it exaclty? if we say its exaclty 3.5mhz, then 3500000 / 32 = 109375 which is around the 110khz mark. substitute the original clock value and it may be more accurate to the real thing. one clock speed i have read was 3579540hz, but i found that the clock in a megadrive 2 i have ( its broken :( ) was 53.203mhz / 15 ( for z80 speed) which gives me 3546866hz which would alter the sound pitches.. hmm, i must get my original mega drive 1 back to see if sega changed the clocks between the two models, or perhaps the mega drives/genesises (which a powerbase converter) sound different to a sms.. Quote > I have been using the info from the file richard.txt in the S8-dev archives, which is almost entirely correct. > It is demonstrably wrong, however, in its suggestion of 125,000 Hz for the PSG clock (could this be the > correct value for a PAL or SECAM system?). > What is the correct value for an NTSC system? > --Nyef

Nyef Guest	Posted: Wed Sep 08, 1999 1:12 pm
Nyef Guest	Quote > what is the clock frequency of the sms? its around 3.5 mhz, but what is it exaclty? XTAL1 is 10.7386 MHz. Divide by 3 to get 3.579533333333 (a close match for the NTSC color subcarrier, if anyone cares). Quote > if we say its exaclty 3.5mhz, then > 3500000 / 32 = 109375 which is around the 110khz mark. substitute the original clock value and it may be more accurate to the real thing. This sounds reasonable. I'll try it tonight to see if it's better than what I'm currently using. Quote > one clock speed i have read was 3579540hz, but i found that the clock in a megadrive 2 i have ( its broken :( ) was 53.203mhz / 15 ( for z80 speed) which gives me 3546866hz which would alter the sound pitches.. One of the signals in any NTSC color video game system has to come close to 3.579545 in order to work. It it's too far off the mark, the system doesn't work. Quote > hmm, i must get my original mega drive 1 back to see if sega changed the clocks between the two models, or perhaps the mega drives/genesises (which a powerbase converter) sound different to a sms.. Hrm... I'll have to try the power base again. And I'll see if any of the genesis systems I have have that 9-pin expansion connector while I'm at it... --Nyef

Zoop Joined: 24 Jun 1999 Posts: 1732 Location: Paris, France	Posted: Wed Sep 08, 1999 5:55 pm
	The Game Gear clock is 3.579545 mhz. I don't know exactly the SMS, but it should be the same. Game Gear is refreshed at 60 hz.

Chris Guest	Correct Posted: Wed Sep 08, 1999 9:54 pm
Chris Guest	That is so true. Pal and NTSC games will play the exact same tones and frequencies but at a different tempo due to the Vints. NTSC is 50 and PAL is 60. Chris :o)

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