calling all msx uk based users

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By Grauw

Ascended (9343)

Аватар пользователя Grauw

10-02-2015, 01:55

I like to listen to this song and then imagine we had MSX PSG trackers like that :).

Atari trackers like this use its fast 16-bit CPU and high resolution timer interrupts to get pulse waves and digidrums. Hard to achieve on MSX, but it could get pretty far I bet! Using the hblank 15 kHz timer and some smart tables for digidrums and pulse waves… Obviously little time left to do anything else.

Here’s a PSG pulse wave test (source) I made a little while ago which plays back a pulse wave on the MSX. Just plainly timed with Z80 wait loops, nothing fancy with hsync and LUTs. Use recent openMSX builds to get a straight pulse wave, use older openMSX builds to get a nice pulse width modulation :).

Anyway that kind of advanced trickery aside, I’ve got to say I have also heard a lot of great PSG music on MSX, especially in scene products.

By tvalenca

Paladin (747)

Аватар пользователя tvalenca

10-02-2015, 16:29

First of all, Z80 clock on a CPC is 4 MHz, so it's natural to have the PSG running at half bus clock speed like in MSX. (and so, l_oliveira is right to infere that it is running at 2MHz) Since the PSG uses the clock input to generate it's sound, music will sound different on each model, a little higher pitched on CPC (but not a full or a half tone, I'm talking about micro-tones). This alone could be mistaken by bad sound quality for untrained ears.

Second, you have all the sound mixing issues that l_oliveira and flyguile pointed.

The fairest way to do such comparision is lifting the 3 sound outputs from the AY chip on each machine (Speccy +2 too if desired) and use the same mixer layout on all computers. I'm not sure, but I think it could be based on the AY datasheet suggestion. Each system still sound "detuned" when compared to the other, (due to different bus clock speeds, Spec +2 is 1.75MHz, MSX is 1.7897MHz, and CPC is 2.0MHz, all of them are bus speed divided by two) but sound quality has to be the same.

By hit9918

Prophet (2897)

Аватар пользователя hit9918

10-02-2015, 19:35

The ST doesn't have a different chip, it has timer interrupt + fast cpu. I am yet to see an AY clone with real different feature.

@grauw, does the demo go with reloading the frequency register?

One doesnt need the usual interrupt rate to make digi, one just needs to reload frequency register to make different length arms.
The cpu load is much less than digi.
The nice thing is that the cpu can even be a bit late on this and jitter and it doesn't matter. The tone is perfect.
Because the bitflip is decided by AY counter / comparator (the frequency register).
The AY started counting from 0 and when you tell the new comparator value a bit later, it doesn't matter.

When timer granularity is too little, the wait time should be rather rounded up than down.
Poking to early means before AY has gotten to the flip, messes the result.

Still in the long run the timer interrupt must be exactly same hz.
When timer granularity is little, every soandso time there is some hiccup.
When starting a tone, make phase reset. When tone is short enough, no hiccup.

Well I again wonder whether 9938 sends interrupts with opened borders.
Then MSX2 could sound like the ST.

Another idea: the game for every of its loop makes a cycle estimation. With that simulate a timer interrupt.
Again, this method can stand cpu jitter and still sound clean.

Wait... it should take no more cpu to not use two arms, but say 4 different arms.
Then AY becomes synthesizer Smile

By flyguille

Prophet (3028)

Аватар пользователя flyguille

10-02-2015, 19:36

Just talking about it, check this just new video from computerphile channel.

youtube

By Grauw

Ascended (9343)

Аватар пользователя Grauw

11-02-2015, 00:54

I copied the above posts into a new thread AY3 PSG duty cycle & digidrum effects

By valkyre

Champion (455)

Аватар пользователя valkyre

11-02-2015, 12:04

Meanwhile.... getting back to the core of this thread - did all the uk users receive my email last week? If not please mail me and i will re send.

By jonesypeter

Expert (74)

Аватар пользователя jonesypeter

23-02-2015, 20:47

Hi. Please see my post on UK magazines. Best wishes

By Hit-Biter

Rookie (30)

Аватар пользователя Hit-Biter

03-11-2018, 22:15

Hi Guys, Im late to the party but my MSX interest has returned after a 30 year break. Looking to get into basic programming and then maybe Machine Code or some other language depending on resources available. Would love to hear from anyone selling or giving away books on MSX. Also looking to complete my MSX Computing and MSX User collections. Contact me if you can help.

Woould love to hear from any user group or club here in the UK. I am in remote part of Scotland so cant visit but this new MSX thing is great >< : )

By valkyre

Champion (455)

Аватар пользователя valkyre

03-11-2018, 22:30

@hit-biter. I will send you an email over the next couple of days with some info.

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