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Changing instrument speed in RMT when playing


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i try to playback an RMT in Mad Pacal (PAL, 50 Hz, the song is Somewhere by PG,

https://demozoo.org/music/125553/)-- but i call it via DLI instead of VBL.

if i call it once per DLI it sounds much too slow. i need to call it trice during DLI

to make it sound normal.

 

i have no knowledge on RMT, but i think that certain C64 trackers need to be

called more than once every frame to allow for better sound/extra effects,

and the feature file for the track contains ```FEAT_INSTRSPEED equ 3```

so i suppose that is the reason? if so, is there any way to convert the track

to INSTRSPEED 1? i would expect that i loose some quality then? or is it

not possible altogether without 'remixing' the track? or can i just change that

in RMT before exporting the stripped RMT? 

 

sorry, if this is clear, but could not find documentations that i understand.

 

 

 

thanks for any help!

 

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I'm no expert on it here but - if you increase the number of RMT calls to get more iterations per frame you won't lose quality.

A trick to get PAL/NTSC at the (almost) same tempo is to skip every 6th call on NTSC, generally it's not noticable.

 

On the other end of the scale to get more finess with portamento as an example, more calls per frame can help - but of course note that you'll be burning about the same number of cycles per call - in some songs you get that scanline colour change representation of how long each RMT call is taking which is generally that 10-20 scanlines worth.

If you wanted 3 calls per frame then you'd probably want to do 1 in VBlank and the other two spaced accordingly down the screen for NTSC or PAL.

So for NTSC probably about 90 and 175 scanlines after VSync, and 110 and 215 for PAL.

 

If CPU usage becomes a problem there's always the option of having the entire song packed and played back from memory resident samples - there was a thread on that some time back, I think it uses compression to store all the required register changes and is useful to save CPU though at the cost of potentially significantly more memory usage.

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7 minutes ago, Rybags said:

I'm no expert on it here but - if you increase the number of RMT calls to get more iterations per frame you won't lose quality.

A trick to get PAL/NTSC at the (almost) same tempo is to skip every 6th call on NTSC, generally it's not noticable.

 

On the other end of the scale to get more finess with portamento as an example, more calls per frame can help - but of course note that you'll be burning about the same number of cycles per call - in some songs you get that scanline colour change representation of how long each RMT call is taking which is generally that 10-20 scanlines worth.

If you wanted 3 calls per frame then you'd probably want to do 1 in VBlank and the other two spaced accordingly down the screen for NTSC or PAL.

So for NTSC probably about 90 and 175 scanlines after VSync, and 110 and 215 for PAL.

 

If CPU usage becomes a problem there's always the option of having the entire song packed and played back from memory resident samples - there was a thread on that some time back, I think it uses compression to store all the required register changes and is useful to save CPU though at the cost of potentially significantly more memory usage.

 

thanks!

 

but, sorry, it seems i was unclear about my goal:

i need the other way around, the song needs to be called three times per frame

to sound correct, but i dont have that CPU time, so what can i do to 'reduce quality'

and call it only once per frame? can i somewhere in RMT change the instrument

speed to 1, and save it, and be done with it? or is this a no-go, because one would

need to change the whole track to get this? or is there any other trick?

as said, i am not afraid to sacrifice sound quality.

 

also, i am very low on memory, so the packing option you mentioned will not

work for me 😕

 

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