FlorentFlament / stella-lag

Code to illustrate lag between image and sound on the Stella emulator

• Compile main.bin with make
• Run the code with stella main.bin or make run

The code changes the background color at the same time it changes the audio. When the screen is white, the TIA plays white noise; when the screen is black, no sound should be heard.

Here's the relevant code:

fx_vblank SUBROUTINE
        lda framecnt
        and #$20
        bne .white
.black:
        lda #$00
        jmp .color_chosen
.white:
        lda #$ff
.color_chosen:
        sta COLUBK
        sta AUDV0
        rts

When running main.bin in Stella 6.3 (stella 6.0.2 as well), I can experience a lag between the picture and the sound (Rough estimate about 50-100 ms). When running the same binary on the real hardware I don't see/hear any lag.

As I don't notice any lag when playing a video on my machine, I don't think my OS (Linux Ubuntu 20.04) introduces it. It feels like it comes from the Stella emulator (Even though I selected "Ultra Quality, minimal lag", in the Audio Mode options).