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Talk:Videos/Digital Show and Tell

806 bytes added, 14:26, 14 February 2014
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I just watch the video and has one question. During demonstration which Monty has feed generator at various frequency and convert to digital at 44.1KHz and convert back to analog and show the analog result at second oscilloscope which is the good way to show the whole digital way of encode and decode. At 1KHz sine wave input, when sampling at 44.1KHz, there will be 44.1 sampling per sine wave or 22 sampling per half sine wave which is not too bad to represent the sine wave and the output from digital-to-analog should still be quite close to original sine wave. However, at input of 20KHz, there will be only 2.2 sampling per sine wave or just 1 sampling per half wave and it merely enough to represent sine wave. My question is if there is just one sampling per half wave, how can the output from digital-to-analog is still be very good sine wave. If 20KHz is sampling at 192KHz, there will be 9.6 sampling per sine wave or 4.8 sampling per half wave which is far from perfect but still better than one. Does this mean that we should have better output if we increasing the sampling from 44.1KHz to 192KHz? --[[User:Somchaisis|Somchaisis]] 05:37, 25 August 2013 (UTC)
: You'll have exactly the same 20 kHz sine wave at 192 kHz as 44.1 kHz. Watch 6m 40s - 7m 06s again. Only two sample points are needed to perfectly recreate a sine wave - any extra samples are <s>redundant</s> superfluous. --[[User:Leorex|Leorex]] 09:29, 15 January 2014 (PST)
: 2.2 samplings per period is enough to fully recreate the original sine wave. It's counterintuitive, but try and think of it like this. You know the input signal (analog) is band-passed to 20kHz, so there are no frequencies higher than 20kHz to be reconstructed. Now look at the 2.2 samples per period; try and draw a continuous line through all the samples without using any frequencies above 20kHz. The maximum frequency of 20kHz limits how "quickly" you can rise or fall the slope of the line. So in fact, there is only *1* solution for the line you draw through the sampling points. Even down to 2 samples per period you can 100% recreate the original analog signal. You will not get better output by increasing the sampling rate to 192kHz, because you have already reconstructed 100% of the signal.
Thank you for the entertaining and educational demo. You have a natural talent for explaining complicated concepts. I studied signals and systems at university and I swear you managed in 30 minutes to explain the same material that took my professors nearly 6 months! I'm looking forward to your next show and tell. [[User:Nhand42|Nhand42]] 12:54, 14 February 2014 (PST)

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