Thank you for pointing out that the 70 Hz is a modulation rate, not an audio frequency. That's exactly right. I wish I could find someone in Korea to help me with the hardware side, but no matter how hard I've tried to persuade people, I've mostly been ignored. As for the Lean part, I wasn't sure whether it was really necessary. I've never been part of academia, so I'm still very clumsy and amateurish at this. Even so, I'll keep doing my best to find someone who can help with the hardware side. Thank you for your kind words.