beep boop, it's harmony time - get outta here szynalski tone generator
also check out the a = 432Hz superior version
master gain: 0%
frequency: 87.307Hz
gain: 100%
frequency: 349.228Hz
frequency: 440Hz
gain: 90%
frequency: 523.251Hz
gain: 60%
frequency: 659.255Hz
gain: 40%