Kernel abuse and sound?

[iesposta]

Bear with me for a bit.

In tweaking batari Basic, my game has a non-standard line count, 270, and 58.22 fps as opposed to 60 fps.

I know that there is the specifications that are considered optimal, but even with games dead on that spec it is still said the Atari 2600 produces an odd signal, right?

Also, many game are way, way off and displays handle things just fine.

 

What I noticed is that the pitch of the music is slightly altered in my game due to the slower frames per second. (The human ear can detect the smallest changes.)

Of course things will sound different if a note is played at 60 fps as opposed to 58.22 fps. Those fps are what Stella reports.

 

Can a kernel be made to change fps down and back up?

In theory this would produce a vibrato effect.

If that is possible how far could it be pushed and keep a stable picture, I wonder?

Or the Atari could play a tune and have each note played at a different fps to make them in tune.

 

Something for assembly coders to try, or I'll revisit this as I learn to make an assembly kernel.

 

Remember to think differently.

[Rybags]

On real hardware the TIA generated sounds should be the same. Only difference being PAL vs NTSC due to different master clock speed.

 

Of course if your line count and frame rate differs then the tempo is going to be different assuming music playback with tracker driven at VSync interval. If you're doing sample playback it shouldn't matter if it's based on scanlines or multiples of per wave step (aside from the 2 things mentioned already).

 

I suspect if you're getting pitch variations in emulation then the emulator is the problem, possibly it thinks the game is running on PAL and adjusts accordingly - there's no firm way of knowing if a game is intended for PAL or NTSC other than checking CRC of known Rom variants or (more likely) having a # of scanline threshold that it assumes should be PAL.

[iesposta]

On real hardware the TIA generated sounds should be the same. Only difference being PAL vs NTSC due to different master clock speed.

...

Yes. That make sense.

A hardware generate tone would be the same despite changes in the video signal.

 

I may have remembered it wrong, hearing the slower tempo and thinking the pitch had changed.

[Rybags]

Tempo is a definite thing - since 2600 has no Interrupt capability and video generation is so CPU intensive, games generally just have to live with the frame rate differences.

Although with music you can always just skip the playback call every 6th frame on NTSC to give the same tempo as PAL, albeit with slight jitter but it'd be mostly unnoticable.