Fix multiple white noise instances

Audio.h

 #define Audio_h_
 
 #if TEENSYDUINO < 120
-#error "Teensyduino version 1.20 or later is required to compile the Audio library"
+#error "Teensyduino version 1.20 or later is required to compile the Audio library."
+#endif
+#ifdef __AVR__
+#error "The Audio Library only works with Teensy 3.X.  Teensy 2.0 is unsupported."
 #endif
 
 // When changing multiple audio object settings that must update at
 #include "synth_whitenoise.h"
 #include "synth_pinknoise.h"
 
-// TODO: more audio processing objects....
-//  waveforms with bandwidth limited tables for synth
-
 #endif

synth_whitenoise.cpp

 	release(block);
 }
 
+uint16_t AudioSynthNoiseWhite::instance_count = 0;
 
 

synth_whitenoise.h

 class AudioSynthNoiseWhite : public AudioStream
 {
 public:
-	AudioSynthNoiseWhite() : AudioStream(0, NULL), level(0), seed(1) {}
+	AudioSynthNoiseWhite() : AudioStream(0, NULL) {
+		level = 0;
+		seed = 1 + instance_count++;
+	}
 	void amplitude(float n) {
 		if (n < 0.0) n = 0.0;
 		else if (n > 1.0) n = 1.0;
 private:
 	int32_t  level; // 0=off, 65536=max
 	uint32_t seed;  // must start at 1
+	static uint16_t instance_count;
 };
 
 #endif