[chbot] Software filter. Fast attack, slow decay

[Mark Atherton]

I have a similar design in VERILOG that clocks at 50MHz and can process 
real-time video, but probably not of immediate use to you.

starting point is full-wave rectifier with peak hold. This emulates the 
diode and cap.

Then you need a leak - every sample, multiply the previously held peak 
by nearly 1.0 (0.999995) so you get the required decay time.

I can talk you through it at the meeting tomorrow eve if that helps.

-mark



On 19/06/2022 4:34 PM, Robin Gilks wrote:
> Here's another question for you all!!
> 
> I'm trying to implement "something like" a VU Meter in software (in an 
> embedded system so it has to be small & fast).
> The hardware equivalent to a diode running into an RC filter
> 
>            |\ |             R
>     in ----|  |----------vvvvvv--------- out
>            |/ |                    |
>                                   ___
>                                   ___  C
>                                    |
>                                    |
>   common ----------------------------------------
> 
> My first port of call for filters is an IIR but that does not have the 
> fast attack I'm after, especially if I want the long tail.
> 
> Does anyone have any magic that doesn't disappear into a morass of DFTs 
> and FFTs and 3 page equations summing integrals from 0 to infinity ;)
> 
> Cheers - hopefully see you tomorrow.
> 
> -- 
> Robin Gilks
> 
> 
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