| "FM Synthesis" is a generic term that encompasses both phase modulation and frequency modulation. And in John Chowning's original article, he bops back and forth between the two without mentioning it. In practice, phase modulation is more useful and makes more sense. And yes, the DX-7 uses phase modulation throughout. --- With Frequency Modulation, you can have an operator feed back on itself. However... with such an arrangement it is entirely possible for it to get stuck at 0 Hz. Not very musical. --- And phase modulation makes a lot more sense. Watch as I demonstrate. Student: "How does FM synthesis work?" Teacher: "Well, do you know what happens if we have one oscillator modulating the frequency of another oscillator?" Student: "You mean like vibrato?" Teacher: "Yes, exactly. Now imagine a vibrato at the same frequency as the second oscillator." Student: "That's doesn't even make sense." Teacher: "Not to worry, the Bessel Functions still apply." Student: "What's a Bessel Function. Can I calculate it?" Teacher: "Not directly. It's kind of complicated." Student: "Mutherfucker!" Okay, now let's try phase modulation. Student: "How does phase modulation work?" Teacher: "Okay... Do you know how distortion works?" Student: "I'm a guitar player. I'm intimately familiar with distortion." Teacher: "Great! So distortion is a nonlinearity on the Y axis of a waveform." Student: "Yep!" Teacher: "Well, phase modulation is a nonlinearity on the X axis of a waveform. We stretch the waveform here [hand gesture], and compress the waveform over here [hand gesture]." Student: "Hmm, warping the waveform along the X axis. That sounds kind of like PWM." Teacher: "It's kind of similar, yeah." Student: "Cool; thanks. I understand." |