MultiPCM: High-pitched noise with single-shot samples.

[ValleyBell]

MAME version

0.261 (g2b20c5ef178)

System information

Ubuntu 23.10

INI configuration details

N/A

Emulated system/software

Virtua Racing (vr), other systems using MultiPCM/YMW258

Incorrect behaviour

"One-short samples" that are terminated by looping over only 1 value can cause audible noise at the point where they should end.
The bug was introduced by #11105.

Expected behaviour

One-shot samples should be silent after they finish.

Steps to reproduce

In Virtua Racing, enter Service Mode -> Music Test and play the song SELECT.

You will hear a quiet but noticeable high pitched sound everytime the kick drum sample ends, which keeps playing until the kick restarts.

Additional details

I think the issue is caused by the interpolation code here:

mame/src/devices/sound/gew.cpp

Lines 595 to 606 in a3c9dd3

	slot.m_offset += step;
	if (slot.m_offset >= (slot.m_sample.m_end << TL_SHIFT))
	{
	slot.m_offset -= (slot.m_sample.m_end - slot.m_sample.m_loop) << TL_SHIFT;
	// DD-9 expects the looped silence at the end of some samples to be the same whether reversed or not
	slot.m_reverse = false;
	}
	if (spos ^ (slot.m_offset >> TL_SHIFT))
	{
	slot.m_prev_sample = csample;
	}

When the loop is only 1 sample value long, it doesn't update slot.m_prev_sample and will keep interpolating between data[end-2] and data[end-1] when it should stay at data[end-1].

[devinacker]

Good catch. I guess it probably got broken by a fix I made to sample length loops in that PR. I'll submit a fix sometime soon if nobody else does.