Actually, yes. If you play a PCM clip, be it sound effect or whatever, you're going to hear a honking big glitch in the PCM with dma that lasts more than a few scanlines.Oerg866 wrote:Actually no, it's not that big of a deal. We once did DMA stuff with music, the engine survives with minimal cpu time. You'll notice a little flakyness. But in honesty, you either skillfully use the YM and PSG to their fullest without relying on PCM too much or you just don't belong in that field, end of story. PCM-Only stuff on Mega Drive is LAME.Chilly Willy wrote:What would suffer the most with DMA direct color is PCM via the YM2612 - unless you only did a line or two, you'd have a BIG click everyframe. Even a low sample rate wouldn't help. But just using FM updated in the vblank wouldn't have a problem.
Let's do some math... 1 scanline is about 63.5 microseconds. Let's take an extremely crappy PCM clip you'd be embarrassed to play on an 8-bit system... say 4kHz. That's 250 microseconds per sample - which is 3.93 scanlines per sample. So even a ridiculously tiny one cell tall DMA (8 scanlines) will hold off the PCM for two sample periods... well within the hearing of even an average gamer. Using 100 lines will hold off the PCM for 25 samples, and if you can't hear that, you're deaf!
The problem gets worse the higher the PCM sample rate. At 12kHz, a 200 line DMA will hold off the PCM for 150 samples.
Remember that this delay is for EVERY SINGLE FRAME of the display, and periodic noise is FAR more easily heard than random noise... which is just noise. You have the equivalent of a 60 Hz square wave added to your PCM.
Now if you're playing a 1kHz sample, MAYBE the sample is sooooooo crappy you won't notice the pop from the DMA, but who's going to use PCM that bad?