Minor filter example fixes and tweaks

Signed-off-by: Christopher Arndt <chris@chrisarndt.de>

examples/multimode_filter.nim

@@ -24,7 +24,7 @@ type
 proc instantiate(descriptor: ptr Lv2Descriptor; sampleRate: cdouble;
                  bundlePath: cstring; features: ptr ptr Lv2Feature):
                  Lv2Handle {.cdecl.} =
-     var plug = createShared(SVFPlugin)
+     let plug = createShared(SVFPlugin)
      plug.svf = initFilterSV(fmLowPass, sampleRate)
      return plug
 
@@ -56,7 +56,7 @@ proc activate(instance: Lv2Handle) {.cdecl.} =
 
 proc run(instance: Lv2Handle; nSamples: cuint) {.cdecl.} =
     let plug = cast[ptr SVFPlugin](instance)
-    plug.svf.setMode(plug.mode[].int.clamp(0, 4).FilterMode)
+    plug.svf.setMode(plug.mode[].int.clamp(0, 3).FilterMode)
     plug.svf.setCutoff(plug.cutoff[].clamp(16.0, 7_000.0))
     plug.svf.setQ(plug.q[].clamp(0.8, 10.0))
     plug.svf.calcCoef()

examples/svf.nim

@@ -1,5 +1,7 @@
 ## State Variable Filter after Hal Chamberlin, Musical Applications of Microprocessors
+##
 ## Only stable up to fc ~= fs / 6.5 !
+## Sensible range for q ~= 0.8 .. 10.0
 
 import std/math
 
@@ -18,23 +20,23 @@ type
         a: float
         b: float
         maxCutoff: float
-        sampleRate: float
+        sampleRate: float64
         needs_update: bool
 
 
 proc reset*(self: var FilterSV) =
-    self.lowPass = 0
-    self.hiPass = 0
-    self.bandPass = 0
-    self.bandReject = 0
+    self.lowPass = 0.0
+    self.hiPass = 0.0
+    self.bandPass = 0.0
+    self.bandReject = 0.0
 
 
-proc initFilterSV*(mode: FilterMode = fmLowPass, sampleRate: float = 48_000): FilterSV =
+proc initFilterSV*(mode: FilterMode = fmLowPass, sampleRate: float64 = 48_000.0): FilterSV =
     result.mode = mode
     result.sampleRate = sampleRate
     result.reset()
-    result.a = 0
-    result.b = 0
+    result.a = 0.0
+    result.b = 0.0
     result.maxCutoff = sampleRate / 6.0
     result.needs_update = true
 
@@ -52,7 +54,7 @@ proc calcCoef*(self: var FilterSV) =
 
 
 proc setCutoff*(self: var FilterSV, cutoff: float) =
-    let fc = if cutoff > self.maxCutoff: self.maxCutoff else: cutoff
+    let fc = min(self.maxCutoff, cutoff)
 
     if fc != self.cutoff:
         self.cutoff = fc