Understanding Oscilloscopes - High Definition Mode

[@senthilsenthil8181]

Lovely presentation 🌹🌹🌹🌹🌹

[@amirb715]

Great video, thanks. Is the low pass filter used for HD mode an IIR filter or FIR filter? at least in R&S scopes

[@pauldenisowski]

Thanks! And it's a FIR filter :)

[@krish2nasa]

Informative, Thank you very much.

[@piotrts]

The aliasing will be nowhere near as bad as you show at 5:20. What you are showing is the effect of subsampling. Averaging acts as a low-pass filter. With averaging, aliasing will be at least 80% lower than what is shown. Of course, a fancy filter will push it nearly to 0 at the cost of increased processing power requirement. Why not show realistic plots? It is improvement anyway. Pushing marketing "altered reality" just leaves a bad taste. Your target audience can see through this.

[@pauldenisowski]

Cześć Piotrze! Sorry to hear that you didn't like the graphic: I intentionally chose a sample rate that is clearly much too low for the input waveform. I do have to say that I've seen even worse mismatches between sample rate and peak input waveform frequency in real world applications :) However, the point of the slide was to show that high resolution mode can be dangerous because the sample rate is reduced but -- unlike high definition mode -- the resulting (reduced) sample rate is not explicitly specified or known. It's not inconceivable that the reduced sample rate caused by decimation in high resolution mode could be significantly less that the Nyquist criterion, and this is why high definition mode is preferable in most cases. It sounds like you were looking for something deeper on the effect of sampling rate, etc. and I'm actually currently working on a video that covers sampling rate in oscilloscopes. If you're interested in seeing more "realistic" examples made using real oscilloscope data and/or MATLAB, I would probably refer you to that video. Thanks for the feedback!

[@piotrts]

@@pauldenisowski Dzięki za szybką odpowiedź! I like your videos and find them highly educational. My point was, that the aliasing shown in the video was unnecessarily exaugurated. It would be like that if no averaging was used but simple subsampling. I understand the benefits of having a configurable filter with a sliding window that maintains the original sampling rate. I saw in the comments it is an FIR filter. Can it be applied to each channel independently or is it a global setting? If it is a per-channel setting is there any lag compensation to maintain synchronisation between channels? Looking forward to the new video.

[@pauldenisowski]

@@piotrts Dzięki za wsparcie! With regards to the HD mode FIR filter in R&S oscilloscopes: in the higher-end scopes, the filter is per-channel and for mid- to -lower-end scopes, it's a global setting. For scopes where HD mode can be independently implemented per-channel, we do time-align the channels internally to take the different filter settings into account.

[@piotrts]

@@pauldenisowski Fantastic! You really know what you are doing.

[@senthilsenthil8181]

Lovely presentation 🌹🌹🌹🌹🌹

[@pauldenisowski]

Thank you!