This appens to be a 'fallout' from sdl2_mixer 2.0.2, at least accordingly to the AUR comment I found when I was searching. See 0b100100 comment https://aur.archlinux.org/packages/xnp2
The diff is the one linked in the comments in AUR, it makes audio works for me in Touhou 1 Highly Responsive To Prayers and 5 Mystical Square. Upstream seems dead and I have wip a port for NP2Kai that works, but it could still be worthwile to fix this in the meantime. Index: Makefile =================================================================== RCS file: /home/cvs/ports/emulators/xnp2/Makefile,v diff -u -p -r1.18 Makefile --- Makefile 21 Sep 2023 13:10:27 -0000 1.18 +++ Makefile 21 Nov 2023 18:26:14 -0000 @@ -2,7 +2,7 @@ COMMENT = PC-9801 emulator DISTNAME = xnp2-0.86 EPOCH = 0 -REVISION = 5 +REVISION = 6 CATEGORIES = emulators HOMEPAGE = https://www.nonakap.org/np2/ Index: patches/patch-x11_soundmng_c =================================================================== RCS file: /home/cvs/ports/emulators/xnp2/patches/patch-x11_soundmng_c,v diff -u -p -r1.3 patch-x11_soundmng_c --- patches/patch-x11_soundmng_c 11 Mar 2022 18:59:43 -0000 1.3 +++ patches/patch-x11_soundmng_c 21 Nov 2023 18:24:59 -0000 @@ -1,7 +1,9 @@ -disable asm on i386, PIE uses registers used by asm code. +- disable asm on i386, PIE uses registers used by asm code. +- fix audio ---- x11/soundmng.c.orig Wed Mar 9 02:25:50 2016 -+++ x11/soundmng.c Sat Dec 31 06:21:29 2016 +Index: x11/soundmng.c +--- x11/soundmng.c.orig ++++ x11/soundmng.c @@ -401,7 +401,7 @@ soundmng_setreverse(BOOL reverse) } else { fnmix = satuation_s16x; @@ -20,3 +22,24 @@ disable asm on i386, PIE uses registers void PARTSCALL _saturation_s16(SINT16 *dst, const SINT32 *src, UINT size) { +@@ -1179,8 +1179,9 @@ sdlaudio_callback(void *userdata, unsigned char *strea + SNDBUF_FILLED_QUEUE_REMOVE_HEAD(); + sndbuf_unlock(); + +- SDL_MixAudio(stream, ++ SDL_MixAudioFormat(stream, + sndbuf->buf + (sndbuf->size - sndbuf->remain), ++ AUDIO_S16SYS, + sndbuf->remain, SDL_MIX_MAXVOLUME); + stream += sndbuf->remain; + len -= sndbuf->remain; +@@ -1198,7 +1199,8 @@ sdlaudio_callback(void *userdata, unsigned char *strea + sndbuf_unlock(); + } + +- SDL_MixAudio(stream, sndbuf->buf + (sndbuf->size - sndbuf->remain), ++ SDL_MixAudioFormat(stream, sndbuf->buf + (sndbuf->size - sndbuf->remain), ++ AUDIO_S16SYS, + len, SDL_MIX_MAXVOLUME); + sndbuf->remain -= len; +
