Trackerboy playback speed differs from gbt-player in emulators

[tadashibashi]

Bug description

Trackerboy playback is slightly slower than playback in emulators (tested in SameBoy, Emulicious, GB Studio).
I'm using GB Studio's GBT Player with the same tick speed as in Trackerboy. Either increasing or decreasing tick speed doesn't align.

How to reproduce

1. Write equivalent song with tempo ticks in .mod (F04) file as a .tbm (F40)
2. Play back .mod in GB Studio or build ROM to test in other emulators

Information

• Trackerboy version: v0.6.2

SourceFiles.zip
GBSpeedComparisonFiles.zip

[stoneface86]

Interesting, I'm guessing the naive assumption of a vblank being exactly 59.7 Hz is the cause as each tick gets samplerate / 59.7 samples (with an extra sample on some ticks after accumulating the remainder).

I'll have to test this in the Nim rewrite to see if the same problem occurs there, which would confirm this is an architectural problem with the emulator.

[tadashibashi]

I built a rom outside of GB Studio using their version of gbt-player and it's playing back at the speed of Trackerboy. I have no idea what the issue could be, but it's definitely on their end. Even the example files are playing back at the wrong speed.

Edit: I confirmed with one of the developers (Rulz) that this is an effect of GB Studio 3.0+ sound engine feature. It's running at a 64Hz tick speed to support playing WAV files at an even sample rate. 16384hz / 64 = 256hz (sample update) / 4 = 64hz music update