Steve, OK. I put your denormal-zeroing function w/SSE into the freeverb.cpp code, and when compiling with the SSE option and calling set_denormal_flags() in the activateFreeverb3 function (see below), I get this error wherever asm is called: freeverb/freeverb.cpp: In function `void set_denormal_flags()': freeverb/freeverb.cpp:48: error: can't find a register in class `BREG' while reloading `asm' Do you have an idea of what might be wrong? Here is where I put the call to your function. Does this make sense? void activateFreeverb3(LADSPA_Handle Instance) { Freeverb3 * poFreeverb = (Freeverb3 *)Instance; poFreeverb->mute(); /* call the Steve Harris denormal zeroing function w/SSE flag */ set_denormal_flags(); } --Neil PS: Maybe we should move this discussion to just linux-audio-dev for now PPS: For reference, this is your function for zeroing denormals w/SSE that I am using: #ifdef __SSE__ #include <xmmintrin.h> #endif void set_denormal_flags() { unsigned long a, b, c, d; #ifdef __SSE__ asm("cpuid": "=a" (a), "=b" (b), "=c" (c), "=d" (d) : "a" (1)); if (d & 1<<25) { /* It has SSE support */ _MM_SET_FLUSH_ZERO_MODE(_MM_FLUSH_ZERO_ON); asm("cpuid": "=a" (a), "=b" (b), "=c" (c), "=d" (d) : "a" (0)); if (b == 0x756e6547) { /* It's an Intel */ int stepping, model, family, extfamily; family = (a >> 8) & 0xf; extfamily = (a >> 20) & 0xff; model = (a >> 4) & 0xf; stepping = a & 0xf; if (family == 15 && extfamily == 0 && model == 0 && stepping < 7) { return; } } asm("cpuid": "=a" (a), "=b" (b), "=c" (c), "=d" (d) : "a" (1)); if (d & 1<<26) { /* bit 26, SSE2 support */ _mm_setcsr(_mm_getcsr() | 0x40); } } else { fprintf(stderr, "This code has been built with SSE support, but your processor does not support\nthe SSE instruction set.\nexiting\n"); exit(1); } #endif } -------------Steve Harris wrote:--------------- For something like a reverb the best option is going to be to build with SSE maths and call the function I posed here a week ago or so. There are so many places where denormals can occur in reverbs that youre going to burn a load of CPU trying to kill them. OTOH I'm not sure how that function would interact with the host when loaded as a plugin