[sdiy] VU meter algorithms

rburnett at richieburnett.co.uk rburnett at richieburnett.co.uk
Mon Mar 18 16:38:52 CET 2019


Ahhh, but how high a sample rate do you need to use to be sure that you 
take a sample at the peak of a waveform!?!?!?  ;-)

-Richie,



On 2019-03-18 15:25, Tom Wiltshire wrote:
> Hi all,
> 
> Does anyone know of any good resources on bargraph VU meter
> algorithms, and specifically implementing a “Peak hold” feature?
> 
> I’m trying to write one - well, I *have* written one - but I’m not
> overly impressed with its performance. The “VU meter” portion of the
> code is pretty good: I sample the audio at 40KHz, then rectify it,
> take the highest sample in a block of 16, and then apply an IIR
> smoothing filter with a time constant of about 200msecs. That part
> seems pretty good, although it “under reads” significantly.
> I’m having worse problems with the Peak Hold dot. This has an attack
> of zero (so it never misses a peak) but uses a longer decay time of
> 400msecs or so. But a typical input signal tends to make it jump
> about, so instead of clearly lighting a single LED, it instead lights
> two or three intermittently. This makes the display rather confusing
> to look at.
> 
> I’d thought to just get stuck in and see how it went (and it went ok)
> but I think now might be a good time for a bit of research. This is a
> solved problem, so someone must have dealt with these issues before
> me.
> 
> Thanks,
> Tom
> 
> 
> 
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