AWOL:
But, as you can see, you've introduced a delay into a blink without delay.
Right? With a 7 millisecond full-stop in processing, the highest frequency this synth can handle is 140 hertz. This is a very bass instrument, like piano keys 30 and below.
encoderaudio:
... Could you change it, as an example, for a n00b
You'll only be a noob your first day ea, so jump right in. AWOL is suggesting that you look at the code you have already posted, and see if you can use the millis()-previousMillis timing loop to also change the time between turning the output on and off, thus getting rid of that toxic "delay(7);" statement. That alone limits your timing to a very low frequency. It's a D3 note.
What are you trying to do - make an audio frequency, or make a time standard that other devices will use to synchronize their noisemaking?