Miska Posted February 25, 2011 Share Posted February 25, 2011 Actually, it's pretty simple math in this case. Square wave is composed via additive synthesis of all of the odd harmonics. Yep, that's why I did it in my head and not bothered with calculator. But what I was calculating was where the 3rd harmonic would land in ADC at 44.1 kHz if anti-alias filter was left out. Now if I take it one step further, 5th would be at 6.8 kHz? For seventh I would run for a calculator. Pictures are always nice, so I made one of 19 kHz square wave having 3rd and 5th harmonics, sampled at 48 kHz. The next one (7th harmonic - 133khz) would already be well above the Nyquist frequency for 24/192 recording And the result would be still pretty darn far from a proper square wave when reconstructed. Also, as has been mentioned here already, the transients that a waveform starts and to some degree ends with can have a steep up or down slope, and those require substantial harmonic energy to produce. Yes, and this part especially gets nasty treatment from linear phase decimation filters. What I'm specifically talking about is related to this: http://en.wikipedia.org/wiki/Gibbs_phenomenon Signalyst - Developer of HQPlayer Pulse & Fidelity - Software Defined Amplifiers Link to comment
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