Better music capabilities

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By DarkSchneider

Paladin (769)

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31-05-2018, 17:23

hit9918 wrote:

DarkSchneider, on the one hand you say 200hz timer, on the other hand the atari text talks of a variable interrupt

Are different sources. The 200Hz one is from here:
http://atari-forum.com/viewtopic.php?f=18&t=14204
Seems that the musicmon works at up to 200Hz. Can search for MusicMon on youtube, but ignore the channels with waveform thumbs, they are samples.
But the sentence:

Quote:

Well in musicmon you can set your sounds to be 50,100 or 200Hz which changes the effects applied to the sound

Says that for PSG (non-sampled) effects they use 200Hz. I ignore if that is some way of speaking and internally works different, but why they would do that. Also, the Atari timer C seems to work at 200Hz, so it fits.

Here an example:
Intensity (200Hz)
https://www.youtube.com/watch?v=SWVSbVpEP-8

If you can do that with 200Hz, it is suppossed that with 300Hz even better.

By hit9918

Prophet (2823)

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31-05-2018, 17:35

after just 2 seconds into the vid I again got the same comment:
these tones are much higher than 200hz, not to speak of their overtones,
therefore it is nyquist-impossible that this was done by wiggeling the volume register!!!

the only thing I can imagine is the "arpeggio" corner
and arpeggio is about writing the frequency register

By hit9918

Prophet (2823)

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31-05-2018, 19:02

I tried 200hz arpeggio in audacity. it sounds bad.
now the question is whether the atari stuff has a secret or just hasnt told the spec properly.

By Grauw

Enlighted (7789)

Grauw's picture

31-05-2018, 20:15

Maybe the 200 Hz refers to the tracker step, ADSR and macro speed, and not the timer for the PWM effect? That seems more likely...

Trying to do PWM at 200 Hz, it seems like it would introduce tones under 200 Hz due to aliasing.

By DarkSchneider

Paladin (769)

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01-06-2018, 09:34

Could be, but I see excesive an update cycle of 200Hz for music, and for that music that is not so fast.

@hit9918 arpeggio on Spectrum, at 50Hz:
https://youtu.be/3QA9mpTH3C8
Many other games used it also. It was much used on Spectrum in-game that only has the 50Hz VBLANK interrupt.
Switchblade (I remember very well this game :) )
https://youtu.be/vdOO4hRzSbE

If I had to say, I think that the main problem is that this maybe should be seen from the sound expert POV instead the programmer one, that always will look for generating the theorical perfect waveform, instead looking for generating the effect itself (this is, something that sounds like, instead the theorical one).

Take a look again to the Zelda music:
https://youtu.be/gKXGDuKrCfA
How it modifies slightly the freq. Also in this guy channel:
https://www.youtube.com/playlist?list=PL92E73FD91764173B
What I see from the wave is how they tremble in both axes, this is, they vary their freqs and volume slightly and that generates the vibrating sound that probably we look for.

Let's see the NES. The NEs only have the VBLANK interrupt:
Arpeggio.
https://youtu.be/4HWHneafZ8w
Some interesting things:
https://youtu.be/kl9v8gtYRZ4
Well, it has PWM, but fixed ones, they sound different, but also constant. It does not allow to define att/sus/dec, they are fixed. But introducing variations at 1/60th sec rate, they get the sound effects.

Then I ask, should we step back? Maybe are starting from the hardest point.

But, what about to see what the hardware itself can do? The envelope itself can apply modulation to the square form. Applying variations, put the oscilator and envelope freqs at decimal ratios instead integer, vary the envelope freq slightly to generate vibrating PWM on the square one, modify the square freq and volume, do like in NES and hold the envelope modulation x/60th sec and then turn off envelope or change its shape and see what happens...

On the list I put before, I see many interesting effects applied to base square forms, simply varying its freq and volume.

So, I think there is no need to try to simulate what other chips do, and create its own sound effects for the PSG. Just like they did for the NES, that has its own sound style. But, ignoring the envelope just like until now, can't be achieved, as it allows to get lots of variations combining waves in so many manners, for one channel.

By DarkSchneider

Paladin (769)

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01-06-2018, 11:13

The other Switchblade music, while it shows the intro:
https://youtu.be/eNdENmbxJd4
With interesting effects at 50Hz.

By PingPong

Prophet (3177)

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01-06-2018, 11:26

What's the point? a lot of chips can be misused to do things not originally intented .
Plus the" continuos signal is a square wave" is a non sense. By definition a continuos signal have period infinite.
So taliking about square wave (a function of time) does not make sense at all.
The point is : can the psg output a triangle wave with programmable period?. Yes using the envelope trick.
And if you still are convinced that only square wave is possible i can suggest you to put an oscilloscope on the psg output

By Metalion

Paladin (982)

Metalion's picture

01-06-2018, 13:02

It seems to me that what we're discussing here is not very far from trying to apply a Fast Fourrer Transformation to form a new wave from the PSG using only the square one available. The principle is to break a waveform into discrete signals (here square ones) and modulate them (by frequency and volume) to form it. The problem is that there's only 3 discrete signals available, and therefore the result cannot be very good.

By hit9918

Prophet (2823)

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03-06-2018, 00:00

the future lies in combining multiple channels

By syn

Paragon (1891)

syn's picture

11-06-2018, 00:18

Grauw wrote:

Maybe the 200 Hz refers to the tracker step, ADSR and macro speed, and not the timer for the PWM effect? That seems more likely...

Trying to do PWM at 200 Hz, it seems like it would introduce tones under 200 Hz due to aliasing.

Ive read somewhere that not all trackers on atari use the HW volume envelope but instead do it though "software", thus allowing more flexibility (volume control for instance). I just assumed this 200hz/300hz is the rate of volume change. Something about this is mentioned here https://en.wikipedia.org/wiki/General_Instrument_AY-3-8910 under advanced techniques. But I may be interpreting it wrong.

PingPong wrote:

What's the point? a lot of chips can be misused to do things not originally intented .
Plus the" continuos signal is a square wave" is a non sense. By definition a continuos signal have period infinite.
So taliking about square wave (a function of time) does not make sense at all.
The point is : can the psg output a triangle wave with programmable period?. Yes using the envelope trick.
And if you still are convinced that only square wave is possible i can suggest you to put an oscilloscope on the psg output

You are missing the point of my posts. I know very well what can be done and not be done with a PSG/AY-3 but I was merely stating the "official" technical specifications of the chip(s).

Before any changes/modulation/HW volume envelope, psg/ay can generate square wave and/or noise
just like the OPLL can generate either of TWO waveforms, sine and halve-sine before applying whatever it is FM synthesis uses (total FM noob here)
An the Y8950 (MSX-AUDIO) has only sine.

This is all regardless of what the sound can actually become AFTER. Anyway kinda side-tracked/offtopic/nitpicking on details from my end ;)

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