Better music capabilities

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By Timmy

Expert (88)

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30-05-2018, 17:49

Grauw wrote:

Ok, it seems you are talking about 100% CPU use, thus audio rate modulation after all. But then I don’t get your remark about total clock cycles being equal, modulating with envelopes is almost free on the CPU, so they can be used in-game. Or where interrupts come into play with CPU-driven audio rate modulation, surely you would time it by CPU clock cycles since there’s no sufficiently high freq timer?

Oh, I think we are talking about the same thing. The main point I wanted to make there was that all the current youtube examples in this thread are "100%-CPU-use" songs, but they were described as examples of "envelope-use" songs and that they were used as in-game songs. (But I might have read that wrong.)

By hit9918

Prophet (2853)

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30-05-2018, 17:56

so, there is no chance with AY phase.

and the atari ST thing is made by poking the pulse width into the AY frequency register.
fixed interrupt hz, asyncronous to the tone, the maximum possible pulse width is double the time, halve the Hz, nyquist style.

300hz interrupt, 150hz pulse, 75hz tone when square wave, 37.5hz tone when it was a 25% thing

By hit9918

Prophet (2853)

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30-05-2018, 18:24

300hz interrupt cant make an electric guitar but I imagine it can make effects like the envelope.
the envelope has fixed volume, so the news with the line interrupt effects is the full volume control, ADSR. and you got 3 independant channels.

By Grauw

Enlighted (8064)

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30-05-2018, 18:35

@Timmy Ahh, yes, no, for Atari ST I assume it’s all CPU-driven (via a timer, so maybe not 100%).

hit9918 wrote:

and the atari ST thing is made by poking the pulse width into the AY frequency register.

Are you sure? That’s the first time I’ve read that. From what I’ve read it’s done by toggling the volume.

There’s one possibility to reduce the envelope volume I think, by setting the tone period to 0 or 1 it should output at half the amplitude.

For doing stuff with ADSR envelopes you don’t need 300 Hz, 60 Hz is sufficient.

By yzi

Champion (441)

yzi's picture

30-05-2018, 18:37

The PSG's hardware envelope tuned to high frequencies can make a slightly more "interesting" sound, but it gets boring and irritating quite quickly.

The more powerful and versatile the host computer is, the better the results, but the sound chip's role is diminished. Taken as a whole, the C64 is one of the best 1980s systems for music, if not the best. I'm starting to actually prefer C64 tunes even over a lot of Amiga stuff. A C64 is an actual synth, with a filter and everything, but Amiga is used as a simple PCM player.

By hit9918

Prophet (2853)

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30-05-2018, 18:50

Grauw wrote:

Are you sure? That’s the first time I’ve read that. From what I’ve read it’s done by toggling the volume.

I could swear that we discussed this same topic some months ago Big smile

By hit9918

Prophet (2853)

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30-05-2018, 18:55

when the atari folks poke the volume in 300hz interrupt, then they get a 150hz square wave, nothing else

By hit9918

Prophet (2853)

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30-05-2018, 19:10

I found this
https://www.msx.org/forum/msx-talk/development/ay3-psg-duty-...
something is quoted from another thread

By hit9918

Prophet (2853)

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30-05-2018, 20:16

what I am trying to say is that if you poke a pulse width to AY frequency register, the AY will count to precisely that value, even if the poke was too late.
and one can be quite much late
so much that it is possible to run the whole thing from a fixed interrupt
a software counter estimates where the ay counter is
to tell when the next poke is due

By hit9918

Prophet (2853)

hit9918's picture

30-05-2018, 21:54

DarkSchneider wrote:

Some good examples of "usable on MSX" (no sample channels) setting 4 line interrupts (200Hz for PAL and 240Hz for NTSC):
https://youtu.be/hlXyyW7W9VI

it is unexplainable
it is said to be made by a 240hz interrupt. this means there could be max 120hz tone, but the tones in the video are much higher than 240hz!
the only thing I can imagine is arpeggio. the switching speed being 200hz while the frequencies are much higher.

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