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On your third point. I remember a very good article on control theory which had a hard and often missed point. Which is digital sampling creates far more noise
by Gibbon1 6y ago
On your third point. I remember a very good article on control theory which had a hard and often missed point. Which is digital sampling creates far more noise in the phase domain than the amplitude one. For control loops this is important because stability depends on phase. The upshot is you need a higher sampling rate than you would naively think.
Bob Pease also had some articles on audio. I think he would agree that open loop analog circuits often produce harmonics that people like. And digital and feedback controlled ones tend to produce harmonics people HATE.
- aidenn0 6y agoStability depends on phase being less than 180°. No way does digital sampling introduce even a tiny fraction of that.
- Gibbon1 6y agoThe thing is feedback control systems have specs that fall apart well before the loop becomes grossly unstable. Phase noise due to sampling pushes you closer to that than you would think. Which explains the need for somewhat higher sampling rates.
- aidenn0 6y agoSampling doesn't really introduce significant phase noise though. A single analog filter will introduce frequency-dependent phase shift and that will dominate any tiny phase noise that might happen from sampling.