Nyquist rates again
Yep, I saw. Very good video, particularly the advice about old equipment and analogue scopes - they're not digital, so they can't lie to you.
But his assertion that you don't get a stepped output from a DAC isn't totally right. The DAC takes the input value and converts it to a voltage which stays the same until the next update, which makes the stepped effect. All DAC's do this. Ways of overcoming it is by oversampling and filtering the output at the Nyquist frequency, which removes the steps and takes high-frequency step-change artefacts out. I find the idea that the samples represent a lollipop graph isn't true in the real world.
My experience is indeed with cheap DAC's, and oversampling the output really does help. More expensive DAC's can do this without any external circuitry. When I designed an audio player years ago when triggerable players were really expensive I did used 16-bit data, oversampled on the fly, with 11KHz sample rate to get decent quality voice output. 8KHz didn't work very well at all.
Most of my experience is with ADC's, and I still don't get the result that sampling near they Nyquist rate results in a good rendition of the original wave. If your input is slightly less than half the sample rate for example, you get a gradual increase then decay of the amplitude all the time. I've found that you can feed it up to 1/5 of the sample rate if you want a decent result, and even then it's ragged. I find the Nyquist rate tells you more about aliasing filters than input frequency limits.
He's right about the bit depth though.
Thanks for the comments though, other peoples views are always informative.
Biting the hand that feeds IT
