To be honest I'm a bit surprised that 'just' changing an optimization setting could lead to a (linker?) error.
Here it is:Your code would be interesting indeed.
#include <Audio.h>
AudioSynthWaveformSine sine1;
AudioOutputI2S i2s1;
AudioConnection patchCord1(sine1, 0, i2s1, 0);
AudioConnection patchCord2(sine1, 0, i2s1, 1);
void setup()
{
AudioMemory(1);
pinMode(LED_BUILTIN, OUTPUT);
digitalWrite(LED_BUILTIN, HIGH);
sine1.frequency(1000);
sine1.amplitude(1.0); // 0dB
}
void loop()
{
}